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  • American Chemical Society  (667,158)
  • Wiley-Blackwell  (149,361)
  • American Meteorological Society
  • 2015-2019  (259,794)
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  • 101
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    Variability and trends in surface meteorology and air–sea fluxes at a site off northern Chile (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 3004–3023, doi:10.1175/JCLI-D-14-00591.1.
    Description: Time series of surface meteorology and air–sea exchanges of heat, freshwater, and momentum collected from a long-term surface mooring located 1600 km west of the coast of northern Chile are analyzed. The observations, spanning 2000–10, have been withheld from assimilation into numerical weather prediction models. As such, they provide a unique in situ record of atmosphere–ocean coupling in a trade wind region characterized by persistent stratocumulus clouds. The annual cycle is described, as is the interannual variability. Annual variability in the air–sea heat flux is dominated by the annual cycle in net shortwave radiation. In austral summer, the ocean is heated; the 9-yr mean annual heating of the ocean is 38 W m−2. Ocean cooling is seen in 2006–08, coincident with La Niña events. Over the full record, significant trends were found. Increases in wind speed, wind stress, and latent heat flux over 9 yr were 0.8 m s−1, 0.022 N m−2, and 20 W m−2 or 13%, 29%, and 20% of the respective 9-yr means. The decrease in the annual mean net heat flux was 39 W m−2 or 104% of the mean. These changes were found to be largely associated with spring and fall. If this change persists, the annual mean net air–sea heat flux will change sign by 2016, when the magnitude of the wind stress will have increased by close to 60%.
    Description: This work is supported by the NOAA Climate Observation Division (NA09OAR4320129).
    Keywords: Climate variability ; Trends
    Repository Name: Woods Hole Open Access Server
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  • 102
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    On the crossover of boundary currents in an idealized model of the Red Sea (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1410–1425, doi:10.1175/JPO-D-14-0192.1.
    Description: The west-to-east crossover of boundary currents has been seen in mean circulation schemes from several past models of the Red Sea. This study investigates the mechanisms that produce and control the crossover in an idealized, eddy-resolving numerical model of the Red Sea. The authors also review the observational evidence and derive an analytical estimate for the crossover latitude. The surface buoyancy loss increases northward in the idealized model, and the resultant mean circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In the midbasin, the northward surface flow crosses from the western boundary to the eastern boundary. Numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0, β, and the meridional gradient of surface buoyancy forcing. In the analytical estimate, which is based on quasigeostrophic, β-plane dynamics, the crossover is predicted to lie at the latitude where the net potential vorticity advection (including an eddy component) is zero. Various terms in the potential vorticity budget can be estimated using a buoyancy budget, a thermal wind balance, and a parameterization of baroclinic instability.
    Description: This work is supported by Award USA 00002, KSA 00011, and KSA 00011/02 made by King Abdullah University of Science and Technology (KAUST), by National Science Foundation Grants OCE0927017, OCE1154641, and OCE85464100, and by the Woods Hole Oceanographic Institution Academic Program Office.
    Description: 2015-11-01
    Keywords: Circulation/ Dynamics ; Boundary currents ; Buoyancy ; Ocean circulation ; Ocean dynamics
    Repository Name: Woods Hole Open Access Server
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  • 103
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    Influences of time-dependent precipitation on water mass transformation, heat fluxes, and deep convection in marginal seas (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1822–1842, doi:10.1175/JPO-D-14-0147.1.
    Description: Influences of time-dependent precipitation on water mass transformation and heat budgets in an idealized marginal sea are examined using theoretical and numerical models. The equations proposed by Spall in 2012 are extended to cases with time-dependent precipitation whose form is either a step function or a sinusoidal function. The theory predicts the differences in temperature and salinity between the convective water and the boundary current as well as the magnitudes of heat fluxes into the marginal sea and across the sea surface. Moreover, the theory reveals that there are three inherent time scales: relaxation time scales for temperature and salinity and a precipitation time scale. The relaxation time scales are determined by a steady solution of the theoretical model with steady precipitation. The relaxation time scale for temperature is always smaller than that for salinity as a result of not only the difference in the form of fluxes at the surface but also the variation in the eddy transport from the boundary current. These three time scales and the precipitation amplitude determine the strength of the ocean response to changes in precipitation and the phase relation between precipitation, changes in salinity and temperature, and changes in heat fluxes. It is demonstrated that the theoretical predictions agree qualitatively well with results from the eddy-resolving numerical model. This demonstrates the fundamental role of mesoscale eddies in the ocean response to time-dependent forcing and provides a framework with which to assess the extent to which observed variability in marginal sea convection and water mass transformation are consistent with an external forcing by variations in precipitation.
    Description: This work was initiated at the 2013 WHOI Geophysical Fluid Dynamics Summer Program, which was supported by the National Science Foundation and the Office of Naval Research. This work was also supported by Grant-in-Aid for Research Fellow (25·8466) of the Ministry of Education, Culture, Sports and Technology (MEXT), Japan, the Program for Leading Graduate Schools, MEXT, Japan (YY), and by the National Science Foundation Grant OCE-1232389 (MAS).
    Description: 2016-01-01
    Keywords: Circulation/ Dynamics ; Boundary currents ; Deep convection ; Eddies ; Ocean dynamics ; Atm/Ocean Structure/ Phenomena ; Precipitation
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  • 104
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    The interaction of an eastward-flowing current and an island : sub- and supercritical flow (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2806–2819, doi:10.1175/JPO-D-15-0061.1.
    Description: An eastward-flowing current of a homogeneous fluid with velocity U, contained in a channel of width L, impinges on an island of width of O(L), and the resulting interaction and dynamics are studied for values of the supercriticality parameter, b = βL2/U, both larger and smaller than π2. The former case is subcritical with respect to Rossby waves, and the latter is supercritical. The nature of the flow field depends strongly on b, and in particular, the nature of the flow around the island and the proportion of the flow passing to the north or south of the island are sensitive to b and to the position of the island in the channel. The problem is studied analytically in a relatively simple, nonlinear quasigeostrophic and adiabatic framework and numerically with a shallow-water model that allows a qualitative extension of the results to the equator. Although the issues involved are motivated by the interaction of the Equatorial Undercurrent and the Galapagos Islands, the analysis presented here focuses on the fundamental issue of the distinctive nature of the flow as a function of Rossby wave criticality.
    Description: Supported by the National Science Foundation Grant OCE-0959381.
    Description: 2016-05-01
    Keywords: Circulation/ Dynamics ; Ocean circulation ; Ocean dynamics ; Waves, oceanic
    Repository Name: Woods Hole Open Access Server
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  • 105
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    Mechanisms of tidal oscillatory salt transport in a partially stratified estuary (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2773–2789, doi:10.1175/JPO-D-15-0031.1.
    Description: Tidal oscillatory salt transport, induced by the correlation between tidal variations in salinity and velocity, is an important term for the subtidal salt balance under the commonly used Eulerian method of salt transport decomposition. In this paper, its mechanisms in a partially stratified estuary are investigated with a numerical model of the Hudson estuary. During neap tides, when the estuary is strongly stratified, the tidal oscillatory salt transport is mainly due to the hydraulic response of the halocline to the longitudinal variation of topography. This mechanism does not involve vertical mixing, so it should not be regarded as oscillatory shear dispersion, but instead it should be regarded as advective transport of salt, which results from the vertical distortion of exchange flow obtained in the Eulerian decomposition by vertical fluctuations of the halocline. During spring tides, the estuary is weakly stratified, and vertical mixing plays a significant role in the tidal variation of salinity. In the spring tide regime, the tidal oscillatory salt transport is mainly due to oscillatory shear dispersion. In addition, the transient lateral circulation near large channel curvature causes the transverse tilt of the halocline. This mechanism has little effect on the cross-sectionally integrated tidal oscillatory salt transport, but it results in an apparent left–right cross-channel asymmetry of tidal oscillatory salt transport. With the isohaline framework, tidal oscillatory salt transport can be regarded as a part of the net estuarine salt transport, and the Lagrangian advective mechanism and dispersive mechanism can be distinguished.
    Description: Tao Wang was supported by the Open Research Fund of State Key Laboratory of Estuarine and Coastal Research (Grant SKLEC-KF201509) and Chinese Scholarship Council. Geyer was supported by by NSF Grant OCE 0926427. Wensheng Jiang was supported by NSFC-Shandong Joint Fund for Marine Science Research Centers (Grant U1406401).
    Description: 2016-05-01
    Keywords: Geographic location/entity ; Estuaries ; Circulation/ Dynamics ; Baroclinic flows ; Dispersion ; Shear structure/flows ; Atm/Ocean Structure/ Phenomena ; Diapycnal mixing ; Models and modeling ; Regional models
    Repository Name: Woods Hole Open Access Server
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  • 106
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    Tools for the microbiome : nano and beyond (2016)
    American Chemical Society
    Details
    Publication Date: 2022-05-25
    Description: © American Chemical Society, 2015. This article is posted here by permission of American Chemical Society; copying and redistribution for non-commercial research and education purposes only. The definitive version was published in ACS Nano 10 (2016): 6-37, doi:10.1021/acsnano.5b07826.
    Description: The microbiome presents great opportunities for understanding and improving the world around us and elucidating the interactions that compose it. The microbiome also poses tremendous challenges for mapping and manipulating the entangled networks of interactions among myriad diverse organisms. Here, we describe the opportunities, technical needs, and potential approaches to address these challenges, based on recent and upcoming advances in measurement and control at the nanoscale and beyond. These technical needs will provide the basis for advancing the largely descriptive studies of the microbiome to the theoretical and mechanistic understandings that will underpin the discipline of microbiome engineering. We anticipate that the new tools and methods developed will also be more broadly useful in environmental monitoring, medicine, forensics, and other areas.
    Description: This research was supported by the Office of Naval Research Grant #N000141410051 (P.S.W., G.C.L.W., and T.Y.), the Genomic Science Program of the U.S. DOE-OBER,
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  • 107
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    Impact of two plumes’ interaction on submarine melting of tidewater glaciers : a laboratory study (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 361–367, doi:10.1175/JPO-D-15-0171.1.
    Description: Idealized laboratory experiments investigate the glacier–ocean boundary dynamics near a vertical glacier in a two-layer stratified fluid. Discharge of meltwater runoff at the base of the glacier (subglacial discharge) enhances submarine melting. In the laboratory, the effect of multiple sources of subglacial discharge is simulated by introducing freshwater at freezing temperature from two point sources at the base of an ice block representing the glacier. The buoyant plumes of cold meltwater and subglacial discharge water entrain warm ambient water, rise vertically, and interact within a layer of depth H2 if the distance between the sources x0 is smaller than H2α/0.35, where α is the entrainment constant. The plume water detaches from the glacier face at the interface between the two layers and/or at the free surface, as confirmed by previous numerical studies and field observations. A plume model is used to explain the observed nonmonotonic dependence of submarine melting on the sources’ separation. The distance between the two sources influences the entrainment of warm water in the plumes and consequently the amount of submarine melting and the final location of the meltwater within the water column. Two interacting plumes located very close together are observed to melt approximately half as much as two independent plumes. The inclusion, or parameterization, of the dynamics regulating multiple plumes’ interaction is therefore necessary for a correct estimate of submarine melting. Hence, the distribution and number of sources of subglacial discharge may play an important role in glacial melt rates and fjord stratification and circulation.
    Description: Support to C.C. was given by the NSF Project OCE-1130008 and OCE-1434041. V.M.G. received support from the “Gori” Fellowship.
    Description: 2016-07-01
    Keywords: Geographic location/entity ; Glaciers ; Circulation/ Dynamics ; Buoyancy ; Entrainment ; Ocean dynamics ; Small scale processes ; Models and modeling ; Laboratory/physical models
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  • 108
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    Potential vorticity structure in the North Atlantic western boundary current from underwater glider observations (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 327–348, doi:10.1175/JPO-D-15-0112.1.
    Description: Potential vorticity structure in two segments of the North Atlantic’s western boundary current is examined using concurrent, high-resolution measurements of hydrography and velocity from gliders. Spray gliders occupied 40 transects across the Loop Current in the Gulf of Mexico and 11 transects across the Gulf Stream downstream of Cape Hatteras. Cross-stream distributions of the Ertel potential vorticity and its components are calculated for each transect under the assumptions that all flow is in the direction of measured vertically averaged currents and that the flow is geostrophic. Mean cross-stream distributions of hydrographic properties, potential vorticity, and alongstream velocity are calculated for both the Loop Current and the detached Gulf Stream in both depth and density coordinates. Differences between these mean transects highlight the downstream changes in western boundary current structure. As the current increases its transport downstream, upper-layer potential vorticity is generally reduced because of the combined effects of increased anticyclonic relative vorticity, reduced stratification, and increased cross-stream density gradients. The only exception is within the 20-km-wide cyclonic flank of the Gulf Stream, where intense cyclonic relative vorticity results in more positive potential vorticity than in the Loop Current. Cross-stream gradients of mean potential vorticity satisfy necessary conditions for both barotropic and baroclinic instability within the western boundary current. Instances of very low or negative potential vorticity, which predispose the flow to various overturning instabilities, are observed in individual transects across both the Loop Current and the Gulf Stream.
    Description: Glider operations in the Gulf Stream were supported by the National Science Foundation under Grant OCE-0220769. Glider operations in the Gulf of Mexico were supported by BP. R.E.T. was supported by the Penzance Endowed Fund in Support of Assistant Scientists and the Independent Research and Development Program at WHOI.
    Description: 2016-07-01
    Keywords: Geographic location/entity ; North Atlantic Ocean ; Circulation/ Dynamics ; Boundary currents ; Potential vorticity ; Atm/Ocean Structure/ Phenomena ; Boundary currents
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  • 109
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    Wind sea behind a cold front and deep ocean acoustics (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1705-1716, doi:10.1175/JPO-D-15-0221.1.
    Description: A rapid and broadband (1 h, 1 〈 f 〈 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20-km array in the northeastern subtropical Pacific. The authors associate the jump with the passage of a cold front and focus on the 4- and 400-Hz spectra. At every station, the time of the jump is consistent with the front coming from the northwest. The apparent rate of progress, 10–20 km h−1 (2.8–5.6 m s−1), agrees with meteorological observations. The acoustic radiation below the front is modeled as arising from a moving half-plane of uncorrelated acoustic dipoles. The half-plane is preceded by a 10-km transition zone, over which the radiator strength increases linearly from zero. With this model, the time derivative of the jump at a station yields a second and independent estimate of the front’s speed, 8.5 km h−1 (2.4 m s−1). For the 4-Hz spectra, the source physics is taken to be Longuet-Higgins radiation. Its strength depends on the quantity , where Fζ is the wave amplitude power spectrum and I the overlap integral. Thus, the 1-h time constant observed in the bottom data implies a similar time constant for the growth of the wave field quantity behind the front. The spectra at 400 Hz have a similar time constant, but the jump occurs 25 min later. The implications of this difference for the source physics are uncertain.
    Description: The OBSANP cruise was funded by the Office of Naval Research under Grants N00014-10-1-0987, N00014-14-1-0324, N00014-10-1-0510, and N00014-10-1-0990.
    Keywords: Atm/Ocean Structure/ Phenomena ; Atmosphere-ocean interaction ; Cold fronts ; Marine boundary layer ; Sea state
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  • 110
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    Statistics of nonlinear internal waves during the Shallow Water 2006 Experiment (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 33 (2016): 839-846, doi:10.1175/JTECH-D-15-0221.1.
    Description: During the Shallow Water Acoustic Experiment 2006 (SW06) conducted on the New Jersey continental shelf in the summer of 2006, detailed measurements of the ocean environment were made along a fixed reference track that was parallel to the continental shelf. The time-varying environment induced by nonlinear internal waves (NLIWs) was recorded by an array of moored thermistor chains and by X-band radars from the attending research vessels. Using a mapping technique, the three-dimensional (3D) temperature field for over a month of NLIW events is reconstructed and analyzed to provide a statistical summary of important NLIW parameters, such as the NLIW propagation speed, direction, and amplitude. The results in this paper can be used as a database for studying the NLIW generation, propagation, and fidelity of nonlinear internal wave models.
    Description: This research was supported by the Office of Naval Research Ocean Acoustics Program (322OA) through Grants N00014-10-1-0396 and N00014-11-1-0701.
    Description: 2016-10-18
    Keywords: Geographic location/entity ; Continental shelf/slope ; North America ; Observational techniques and algorithms ; Data processing ; In situ oceanic observations ; Sampling ; Mathematical and statistical techniques ; Statistics
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  • 111
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    Variations of the global net air–sea heat flux during the “hiatus” period (2001–10) (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 29 (2016): 3647-3660, doi:10.1175/JCLI-D-15-0626.1.
    Description: An assessment is made of the mean and variability of the net air–sea heat flux, Qnet, from four products (ECCO, OAFlux–CERES, ERA-Interim, and NCEP1) over the global ice-free ocean from January 2001 to December 2010. For the 10-yr “hiatus” period, all products agree on an overall net heat gain over the global ice-free ocean, but the magnitude varies from 1.7 to 9.5 W m−2. The differences among products are particularly large in the Southern Ocean, where they cannot even agree on whether the region gains or loses heat on the annual mean basis. Decadal trends of Qnet differ significantly between products. ECCO and OAFlux–CERES show almost no trend, whereas ERA-Interim suggests a downward trend and NCEP1 shows an upward trend. Therefore, numerical simulations utilizing different surface flux forcing products will likely produce diverged trends of the ocean heat content during this period. The downward trend in ERA-Interim started from 2006, driven by a peculiar pattern change in the tropical regions. ECCO, which used ERA-Interim as initial surface forcings and is constrained by ocean dynamics and ocean observations, corrected the pattern. Among the four products, ECCO and OAFlux–CERES show great similarities in the examined spatial and temporal patterns. Given that the two estimates were obtained using different approaches and based on largely independent observations, these similarities are encouraging and instructive. It is more likely that the global net air–sea heat flux does not change much during the so-called hiatus period.
    Description: This paper is funded in part by the NOAA Climate Observation Division, Climate Program Office, under Grant NA09OAR4320129 and by the NOAA MAPP Climate Reanalysis Task Force Team under Grant NA13OAR4310106. The study was initiated when X. Liang was a postdoc at MIT, where he was supported in part by the NSF through Grant OCE-0961713, by NOAA through Grant NA10OAR4310135, and by the NASA Physical Oceanography Program through ECCO.
    Description: 2016-11-15
    Keywords: Physical Meteorology and Climatology ; Heat budgets/fluxes ; Surface fluxes ; Models and modeling ; Reanalysis data ; Variability ; Climate variability ; Interannual variability ; Seasonal variability
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  • 112
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    Investigating the eddy diffusivity concept in the coastal ocean (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2201-2218, doi:10.1175/JPO-D-16-0020.1.
    Description: This paper aims to test the validity, utility, and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a high-resolution (800 m) high-frequency radar south of Martha’s Vineyard, Massachusetts. Specifically, this study investigates how well a combination of radar-based velocities and drifter-derived diffusivities can reproduce observed dye spreading over an 8-h time interval. A drifter-based estimate of an anisotropic diffusivity tensor is used to parameterize small-scale motions that are unresolved and underresolved by the radar system. This leads to a significant improvement in the ability of the radar to reproduce the observed dye spreading.
    Description: IR, AK, and SL were supported by the NSF OCE Grant 1332646. IR was also supported by NASA Grant NNX14AH29G.
    Description: 2016-12-29
    Keywords: Circulation/ Dynamics ; Coastal flows ; Diffusion ; Lagrangian circulation/transport ; Observational techniques and algorithms ; Radars/Radar observations ; Models and modeling ; Tracers
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  • 113
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    Reply to “Comments on ‘The interaction of an eastward-flowing current and an island : sub- and supercritical flow’” (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 2267–2268, doi:10.1175/JPO-D-16-0057.1.
    Description: The original article that was the subject of this comment/reply can be found at http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-15-0061.1.
    Description: 2017-01-12
    Keywords: Circulation/ Dynamics ; Circulation/ Dynamics
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  • 114
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    Interaction between a vertical turbulent jet and a thermocline (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3415-3427, doi:10.1175/JPO-D-16-0035.1.
    Description: The behavior of an axisymmetric vertical turbulent jet in an unconfined stratified environment is studied by means of well-resolved, large-eddy simulations. The stratification is two uniform layers separated by a thermocline. This study considers two cases: when the thermocline thickness is small and on the order of the jet diameter at the thermocline entrance. The Froude number of the jet at the thermocline varies from 0.6 to 1.9, corresponding to the class of weak fountains. The mean jet penetration, stratified turbulent entrainment, jet oscillations, and the generation of internal waves are examined. The mean jet penetration is predicted well by a simple model based on the conservation of the source energy in the thermocline. The entrainment coefficient for the thin thermocline is consistent with the theoretical model for a two-layer stratification with a sharp interface, while for the thick thermocline entrainment is larger at low Froude numbers. The data reveal the presence of a secondary horizontal flow in the upper part of the thick thermocline, resulting in the entrainment of fluid from the thermocline rather than from the upper stratification layer. The spectra of the jet oscillations in the thermocline display two peaks, at the same frequencies for both stratifications at fixed Froude number. For the thick thermocline, internal waves are generated only at the lower frequency, since the higher peak exceeds the maximal buoyancy frequency. For the thin thermocline, conversely, the spectra of the internal waves show the two peaks at low Froude numbers, whereas only one peak at the lower frequency is observed at higher Froude numbers.
    Description: This work was supported by the Linné FLOW Centre at KTH (E. E.), the European Research Council Grant ERC-2013-CoG-616186, TRITOS (L. B.), and the Swedish Research Council (VR), Outstanding Young Researcher Award (L. B.). Support to C. C. was given by the NSF Project OCE-1434041.
    Description: 2017-05-10
    Keywords: Jets ; Mixing ; Oscillations ; Thermocline
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  • 115
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    A general-purpose microcontroller-based framework for integrating oceanographic sensors, instruments, and peripherals (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 415-427, doi:10.1175/JTECH-D-16-0069.1.
    Description: Sensors and instruments for basic oceanographic properties are becoming increasingly sophisticated, which both simplifies and complicates their use in field studies. This increased sophistication disproportionately affects smaller-scale observational efforts that are less likely to be well supported technically but which need to integrate instruments, sensors, and commonly needed peripheral devices in ways not envisioned by their manufacturers. A general-purpose hardware and software framework was developed around a widely used family of low-power microcontrollers to lessen the technical expertise and customization required to integrate sensors, instruments, and peripherals, and thus simplify such integration scenarios. Both the hardware and associated firmware development tools provide a range of features often required in such scenarios: serial data interfaces, analog inputs and outputs, logic lines and power-switching capability, nonvolatile storage of data and parameters for sampling or configuration, and serial communication interfaces to supervisory or telemetry systems. The microcontroller and additional components needed to implement this integration framework are small enough to encapsulate in standard cable splices, creating a small form factor “smart cable” that can be readily wired and programmed for a range of integration needs. An application programming library developed for this hardware provides skeleton code for functions commonly desired when integrating sensors, instruments, and peripherals. This minimizes the firmware programming expertise needed to apply this framework in many integration scenarios and thus streamlines the development of firmware for different field applications. Envisioned applications are in field programs where significant technical instrumentation expertise is unavailable or not cost effective.
    Description: Link Foundation Ocean Engineering graduate fellowship to SRL. Subsequent development effort was supported by a NASA New Investigator Award to SRL (NNX10AQ83G) and by the Woods Hole Oceanographic Institution through its Assistant Scientist Endowed Support, a Cecil H. and Ida M. Green Technology Innovation Award, and the Investment in Science Program.
    Keywords: Instrumentation/sensors
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    Long-path quantum cascade laser–based sensor for methane measurements (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 33 (2016): 2373-2384, doi:10.1175/JTECH-D-16-0024.1.
    Description: A long-path methane (CH4) sensor was developed and field deployed using an 8-μm quantum cascade laser. The high optical power (40 mW) of the laser allowed for path-integrated measurements of ambient CH4 at total pathlengths from 100 to 1200 m with the use of a retroreflector. Wavelength modulation spectroscopy was used to make high-precision measurements of atmospheric pressure–broadened CH4 absorption over these long distances. An in-line reference cell with higher harmonic detection provided metrics of system stability in rapidly changing and harsh environments. The system consumed less than 100 W of power and required no consumables. The measurements intercompared favorably (typically less than 5% difference) with a commercial in situ methane sensor when accounting for the different spatiotemporal scales of the measurements. The sensor was field deployed for 2 weeks at an arctic lake to examine the robustness of the approach in harsh field environments. Short-term precision over a 458-m pathlength was 10 ppbv at 1 Hz, equivalent to a signal from a methane enhancement above background of 5 ppmv in a 1-m length. The sensor performed well in a range of harsh environmental conditions, including snow, rain, wind, and changing temperatures. These field measurements demonstrate the capabilities of the approach for use in detecting large but highly variable emissions in arctic environments.
    Description: The authors gratefully acknowledge funding for this work by MIRTHE through NSF-ERC Grant EEC-0540832. D. J. Miller acknowledges support by the National Science Foundation Graduate Research Fellowship under Grant DGE-0646086. K. Sun acknowledges support by the NASA Earth and Space Science Fellowship IIP-1263579.
    Description: 2017-05-01
    Keywords: Arctic ; North America ; Greenhouse gases ; In situ atmospheric observations ; Instrumentation/sensors ; Field experiments
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    Overturning in the Subpolar North Atlantic Program : a new international ocean observing system (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 98 (2017): 737-752, doi:10.1175/BAMS-D-16-0057.1.
    Description: For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.
    Description: The authors gratefully acknowledge financial support from the U.S. National Science Foundation (NSF; OCE-1259102, OCE-1259103, OCE-1259618, OCE-1258823, OCE-1259210, OCE-1259398, OCE-0136215, and OCE-1005697); the U.S. National Aeronautics and Space Administration (NASA); the U.S. National Oceanic and Atmospheric Administration (NOAA); the WHOI Ocean and Climate Change Institute (OCCI), the WHOI Independent Research and Development (IRD) Program, and the WHOI Postdoctoral Scholar Program; the U.K. Natural Environment Research Council (NERC; NE/K010875/1, NE/K010700/1, R8-H12-85, FASTNEt NE/I030224/1, NE/K010972/1, NE/K012932/1, and NE/M018024/1); the European Union Seventh Framework Programme (NACLIM project, 308299 and 610055); the German Federal Ministry and Education German Research RACE Program; the Natural Sciences and Engineering Research Council of Canada (NSERC; RGPIN 227438-09, RGPIN 04357, and RG-PCC 433898); Fisheries and Oceans Canada; the National Natural Science Foundation of China (NSFC; 41521091, U1406401); the Fundamental Research Funds for the Central Universities of China; the French Research Institute for Exploitation of the Sea (IFREMER); the French National Center for Scientific Research (CNRS); the French National Institute for Earth Sciences and Astronomy (INSU); the French national program LEFE; and the French Oceanographic Fleet (TGIR FOF).
    Description: 2017-10-24
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    Entrainment in a dense current flowing down a rough sloping bottom in a rotating fluid (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 485-498, doi:10.1175/JPO-D-16-0175.1.
    Description: Dense oceanic overflows descend over the rough topography of the continental slope entraining and mixing with surrounding waters. The associated dilution dictates the fate of these currents and thus is of fundamental importance to the formation of deep water masses. The entrainment in a dense current flowing down a sloping bottom in a rotating homogeneous fluid is investigated using laboratory experiments, focusing on the influence of the bottom roughness on the flow dynamics. The roughness is idealized by an array of vertical rigid cylinders and both their spacing and height are varied as well as the inclination of the sloping bottom. The presence of the roughness is generally observed to decelerate the dense current, with a consequent reduction of the Froude number, when compared to the smooth bottom configuration. However, the dilution of the dense current due to mixing with the ambient fluid is enhanced by the roughness elements, especially for low Froude numbers. When the entrainment due to shear instability at the interface between the dense current and the ambient fluid is low, the additional turbulence and mixing arising at the bottom of the dense current due to the roughness elements strongly affects the dilution of the current. Finally, a strong dependence of the entrainment parameter on the Reynolds number is observed.
    Description: Support to C. C. was given by the National Science Foundation Project OCE- 1333174. Support to L. O. during her internship at WHOI was provided by the Lions Club ‘‘Napoli Megaride’’ and the Zoological Station Anton Dohrn through the Paolo Brancaccio fellowship (2012).
    Description: 2017-08-20
    Keywords: Density currents ; Entrainment ; Density currents ; Mixing
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    Impact of poleward moisture transport from the North Pacific on the acceleration of sea ice loss in the Arctic since 2002 (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2017): 6757-6769, doi:10.1175/JCLI-D-16-0461.1.
    Description: Arctic sea ice area (SIA) during late summer and early fall decreased substantially over the last four decades, and its decline accelerated beginning in the early 2000s. Statistical analyses of observations show that enhanced poleward moisture transport from the North Pacific to the Arctic Ocean contributed to the accelerated SIA decrease during the most recent period. As a consequence, specific humidity in the Arctic Pacific sector significantly increased along with an increase of downward longwave radiation beginning in 2002, which led to a significant acceleration in the decline of SIA in the Arctic Pacific sector. The resulting sea ice loss led to increased evaporation in the Arctic Ocean, resulting in a further increase of the specific humidity in mid-to-late fall, thus acting as a positive feedback to the sea ice loss. The overall set of processes is also found in a long control simulation of a coupled climate model.
    Description: This work was supported by the National Research Foundation of Korea Grant NRF-2009-C1AAA001-0093, funded by the Korean government (MEST), to HJL, YHK, and MOK. S-WY is supported by the Korea Meteorological Administration Research and Development Program under Grant KMIPA2015-1042. Y-OK is supported by the U.S. Department of Energy (DE-SC0014433) and National Science Foundation (OCE-1242989). WP acknowledges support from the BMBF project CLIMPRE InterDec (FKZ: 01LP1609B).
    Description: 2018-01-26
    Keywords: Pacific decadal oscillation ; Sea surface temperature ; Humidity ; Ice loss/growth
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    Comparison of rip current hazard likelihood forecasts with observed rip current speeds (2017)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Weather and Forecasting 32 (2017): 1659-1666, doi:10.1175/WAF-D-17-0076.1.
    Description: Although rip currents are a major hazard for beachgoers, the relationship between the danger to swimmers and the physical properties of rip current circulation is not well understood. Here, the relationship between statistical model estimates of hazardous rip current likelihood and in situ velocity observations is assessed. The statistical model is part of a forecasting system that is being made operational by the National Weather Service to predict rip current hazard likelihood as a function of wave conditions and water level. The temporal variability of rip current speeds (offshore-directed currents) observed on an energetic sandy beach is correlated with the hindcasted hazard likelihood for a wide range of conditions. High likelihoods and rip current speeds occurred for low water levels, nearly shore-normal wave angles, and moderate or larger wave heights. The relationship between modeled hazard likelihood and the frequency with which rip current speeds exceeded a threshold was assessed for a range of threshold speeds. The frequency of occurrence of high (threshold exceeding) rip current speeds is consistent with the modeled probability of hazard, with a maximum Brier skill score of 0.65 for a threshold speed of 0.23 m s−1, and skill scores greater than 0.60 for threshold speeds between 0.15 and 0.30 m s−1. The results suggest that rip current speed may be an effective proxy for hazard level and that speeds greater than ~0.2 m s−1 may be hazardous to swimmers.
    Description: Funding was provided by the National Science Foundation (1232910, 1332705, and 1536365), and by National Security Science and Engineering and Vannevar Bush Faculty Fellowships funded by the assistant secretary of Defense for Research and Engineering.
    Description: 2018-02-28
    Keywords: Coastlines ; Coastal flows ; Waves, oceanic ; Forecast verification/skill ; Probability forecasts/models/distribution ; Statistical forecasting
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    Photochemical oxidation of oil reduced the effectiveness of aerial dispersants applied in response to the Deepwater Horizon spill (2018)
    American Chemical Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Chemical Society, 2018. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Environmental Science and Technology Letters 5 (2018): 226–231, doi:10.1021/acs.estlett.8b00084.
    Description: Chemical dispersants are one of many tools used to mitigate the overall environmental impact of oil spills. In principle, dispersants break up floating oil into small droplets that disperse into the water column where they are subject to multiple fate and transport processes. The effectiveness of dispersants typically decreases as oil weathers in the environment. This decrease in effectiveness is often attributed to evaporation and emulsification, with the contribution of photochemical weathering assumed to be negligible. Here, we aim to test this assumption using Macondo well oil released during the Deepwater Horizon spill as a case study. Our results indicate that the effects of photochemical weathering on Deepwater Horizon oil properties and dispersant effectiveness can greatly outweigh the effects of evaporative weathering. The decrease in dispersant effectiveness after light exposure was principally driven by the decreased solubility of photo-oxidized crude oil residues in the solvent system that comprises COREXIT EC9500A. Kinetic modeling combined with geospatial analysis demonstrated that a considerable fraction of aerial applications targeting Deepwater Horizon surface oil had low dispersant effectiveness. Collectively, the results of this study challenge the paradigm that photochemical weathering has a negligible impact on the effectiveness of oil spill response and provide critical insights into the “window of opportunity” to apply chemical dispersants in response to oil spills in sunlit waters.
    Description: This work was supported, in part, by National Science Foundation Grant OCE-1333148, Gulf of Mexico Research Initiative Grants 015, SA 16-30, the DEEP-C consortium, and the Clark Family Foundation, Inc. EPA funding was provided to R.N.C. from the Oil Spill Liability Trust Fund.
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    Hydrography of the Gulf of Mexico using autonomous floats (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 773-794, doi:10.1175/JPO-D-17-0205.1.
    Description: Fourteen autonomous profiling floats, equipped with CTDs, were deployed in the deep eastern and western basins of the Gulf of Mexico over a four-year interval (July 2011–August 2015), producing a total of 706 casts. This is the first time since the early 1970s that there has been a comprehensive survey of water masses in the deep basins of the Gulf, with better vertical resolution than available from older ship-based surveys. Seven floats had 14-day cycles with parking depths of 1500 m, and the other half from the U.S. Argo program had varying cycle times. Maps of characteristic water masses, including Subtropical Underwater, Antarctic Intermediate Water (AAIW), and North Atlantic Deep Water, showed gradients from east to west, consistent with their sources being within the Loop Current (LC) and the Yucatan Channel waters. Altimeter SSH was used to characterize profiles being in LC or LC eddy water or in cold eddies. The two-layer nature of the deep Gulf shows isotherms being deeper in the warm anticyclonic LC and LC eddies and shallower in the cold cyclones. Mixed layer depths have an average seasonal signal that shows maximum depths (~60 m) in January and a minimum in June–July (~20 m). Basin-mean steric heights from 0–50-m dynamic heights and altimeter SSH show a seasonal range of ~12 cm, with significant interannual variability. The translation of LC eddies across the western basin produces a region of low homogeneous potential vorticity centered over the deepest part of the western basin.
    Description: The authors were supported by the Department of the Interior, Bureau of Ocean Energy Management (BOEM), Contract M08PC20043 to Leidos, Inc., Raleigh, North Carolina.
    Description: 2018-10-04
    Keywords: Eddies ; Mixing ; Potential vorticity ; Surface layer ; Water masses
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    Wind-wave effects on estuarine turbulence : a comparison of observations and second-moment closure predictions (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 905-923, doi:10.1175/JPO-D-17-0133.1.
    Description: Observations of turbulent kinetic energy, dissipation, and turbulent stress were collected in the middle reaches of Chesapeake Bay and were used to assess second-moment closure predictions of turbulence generated beneath breaking waves. Dissipation scaling indicates that the turbulent flow structure observed during a 10-day wind event was dominated by a three-layer response that consisted of 1) a wave transport layer, 2) a surface log layer, and 3) a tidal, bottom boundary layer limited by stable stratification. Below the wave transport layer, turbulent mixing was limited by stable stratification. Within the wave transport layer, where dissipation was balanced by a divergence in the vertical turbulent kinetic energy flux, the eddy viscosity was significantly underestimated by second-moment turbulence closure models, suggesting that breaking waves homogenized the mixed surface layer to a greater extent than the simple model of TKE diffusing away from a source at the surface. While the turbulent transport of TKE occurred largely downgradient, the intermittent downward sweeps of momentum generated by breaking waves occurred largely independent of the mean shear. The underprediction of stress in the wave transport layer by second-moment closures was likely due to the inability of the eddy viscosity model to capture the nonlocal turbulent transport of the momentum flux beneath breaking waves. Finally, the authors hypothesize that large-scale coherent turbulent eddies played a significant role in transporting momentum generated near the surface to depth.
    Description: This work was supported by National Science Foundation Grants OCE-1061609 and OCE-1339032.
    Description: 2018-10-19
    Keywords: Mixing ; Turbulence ; Waves, oceanic ; Boundary layer
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    An observing system simulation experiment for the calibration and validation of the surface water ocean topography sea surface height measurement using in situ platforms (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 35 (2018): 281-297, doi:10.1175/JTECH-D-17-0076.1.
    Description: The wavenumber spectrum of sea surface height (SSH) is an important indicator of the dynamics of the ocean interior. While the SSH wavenumber spectrum has been well studied at mesoscale wavelengths and longer, using both in situ oceanographic measurements and satellite altimetry, it remains largely unknown for wavelengths less than ~70 km. The Surface Water Ocean Topography (SWOT) satellite mission aims to resolve the SSH wavenumber spectrum at 15–150-km wavelengths, which is specified as one of the mission requirements. The mission calibration and validation (CalVal) requires the ground truth of a synoptic SSH field to resolve the targeted wavelengths, but no existing observational network is able to fulfill the task. A high-resolution global ocean simulation is used to conduct an observing system simulation experiment (OSSE) to identify the suitable oceanographic in situ measurements for SWOT SSH CalVal. After fixing 20 measuring locations (the minimum number for resolving 15–150-km wavelengths) along the SWOT swath, four instrument platforms were tested: pressure-sensor-equipped inverted echo sounders (PIES), underway conductivity–temperature–depth (UCTD) sensors, instrumented moorings, and underwater gliders. In the context of the OSSE, PIES was found to be an unsuitable tool for the target region and for SSH scales 15–70 km; the slowness of a single UCTD leads to significant aliasing by high-frequency motions at short wavelengths below ~30 km; an array of station-keeping gliders may meet the requirement; and an array of moorings is the most effective system among the four tested instruments for meeting the mission’s requirement. The results shown here warrant a prelaunch field campaign to further test the performance of station-keeping gliders.
    Description: The authors would like to acknowledge the funding sources: the SWOT mission (JW, LF, DM); NASA Projects NNX13AE32G, NNX16AH76G, and NNX17AH54G (TF); and NNX16AH66G and NNX17AH33G (BQ). AF and MF were funded by the Keck Institute for Space Studies (which is generously supported by the W. M. Keck Foundation) through the project Science-driven Autonomous and Heterogeneous Robotic Networks: A Vision for Future Ocean Observations (http://kiss.caltech.edu/?techdev/seafloor/seafloor.html).
    Description: 2018-08-07
    Keywords: Altimetry ; In situ oceanic observations ; Profilers, oceanic ; Satellite observations ; Sensitivity studies ; Planning
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    Shelf–open ocean exchange forced by wind jets (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 163-174, doi:10.1175/JPO-D-17-0161.1.
    Description: The general problem of exchange from a shallow shelf across sharp topography to the deep ocean forced by narrow, cross-shelf wind jets is studied using quasigeostrophic theory and an idealized primitive equation numerical model. Interest is motivated by katabatic winds that emanate from narrow fjords in southeast Greenland, although similar topographically constrained wind jets are found throughout the world’s oceans. Because there is no net vorticity input by the wind, the circulation is largely confined to the region near the forcing. Circulation over the shelf is limited by bottom friction for weakly stratified flows, but stratification allows for much stronger upper-layer flows that are regulated by weak coupling to the lower layer. Over the sloping topography, the topographic beta effect limits the deep flow, while, for sufficient stratification, the upper-layer flow can cross the topography to connect the shelf to the open ocean. This can be an effective transport mechanism even for short, strong wind events because damping of the upper-layer flow is weak. A variety of transients are generated for an abrupt onset of winds, including short topography Rossby waves, long topographic Rossby waves, and inertial waves. Using parameters representative of southeast Greenland, katabatic wind events will force an offshore transport of O(0.4) Sv (1 Sv ≡ 106 m3 s−1) that, when considered for 2 days, will result in an offshore flux of O(5 × 1010) m3.
    Description: MAS was supported by the National Science Foundation under Grant OCE-1533170.
    Description: 2018-07-18
    Keywords: Coastal flows ; Downslope winds ; Ocean dynamics
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    On estimating the surface wind stress over the sea (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1533-1541, doi:10.1175/JPO-D-17-0267.1.
    Description: Our study analyzes measurements primarily from two Floating Instrument Platform (FLIP) field programs and from the Air–Sea Interaction Tower (ASIT) site to examine the relationship between the wind and sea surface stress for contrasting conditions. The direct relationship of the surface momentum flux to U2 is found to be better posed than the relationship between and U, where U is the wind speed and is the friction velocity. Our datasets indicate that the stress magnitude often decreases significantly with height near the surface due to thin marine boundary layers and/or enhanced stress divergence close to the sea surface. Our study attempts to correct the surface stress estimated from traditional observational levels by using multiple observational levels near the surface and extrapolating to the surface. The effect of stability on the surface stress appears to be generally smaller than errors due to the stress divergence. Definite conclusions require more extensive measurements close to the sea surface.
    Description: This work was supported by the U.S. Office of Naval Research through Award N00014-16-1-2600. We
    Description: 2019-01-10
    Keywords: Atmosphere-ocean interaction ; Marine boundary layer
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    Observed variations in turbulent mixing efficiency in the deep ocean (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1815-1830, doi:10.1175/JPO-D-17-0275.1.
    Description: Recent progress in direct numerical simulations (DNSs) of stratified turbulent flows has led to increasing attention to the validity of the constancy of the dissipation flux coefficient Γ in the Osborn’s eddy diffusivity model. Motivated by lack of observational estimates of Γ, particularly under weakly stratified deep-ocean conditions, this study estimates Γ using deep microstructure profiles collected in various regions of the North Pacific and Southern Oceans. It is shown that Γ is not constant but varies significantly with the Ozmidov/Thorpe scale ratio ROT in a fashion similar to that obtained by previous DNS studies. Efficient mixing events with Γ ~ O(1) and ROT ~ O(0.1) tend to be frequently observed in the deep ocean (i.e., weak stratification), while moderate mixing events with Γ ~ O(0.1) and ROT ~ O(1) tend to be observed in the upper ocean (i.e., strong stratification). The observed negative relationship between Γ and ROT is consistent with a simple scaling that can be derived from classical turbulence theories. In contrast, the observed results exhibit no definite relationships between Γ and the buoyancy Reynolds number Reb, although Reb has long been thought to be another key parameter that controls Γ.
    Description: This study was supported by MEXT KAKENHI Grant JP15H05824 and JSPS KAKENHI Grant JP15H02131.
    Description: 2019-02-15
    Keywords: Abyssal circulation ; Mixing ; Subgrid-scale processes ; Turbulence ; In situ oceanic observations
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    Distinct mechanisms of decadal subsurface heat content variations in the eastern and western Indian Ocean modulated by tropical Pacific SST (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 7751-7769, doi:10.1175/JCLI-D-18-0184.1.
    Description: Decadal variability of the subsurface ocean heat content (OHC) in the Indian Ocean is investigated using a coupled climate model experiment, in which observed eastern tropical Pacific sea surface temperature (EPSST) anomalies are specified. This study intends to understand the contributions of external forcing relative to those of internal variability associated with EPSST, as well as the mechanisms by which the Pacific impacts Indian Ocean OHC. Internally generated variations associated with EPSST dominate decadal variations in the subsurface Indian Ocean. Consistent with ocean reanalyses, the coupled model reproduces a pronounced east–west dipole structure in the southern tropical Indian Ocean and discontinuities in westward-propagating signals in the central Indian Ocean around 100°E. This implies distinct mechanisms by which the Pacific impacts the eastern and western Indian Ocean on decadal time scales. Decadal variations of OHC in the eastern Indian Ocean are attributed to 1) western Pacific surface wind anomalies, which trigger oceanic Rossby waves propagating westward through the Indonesian Seas and influence Indonesian Throughflow transport, and 2) zonal wind anomalies over the central tropical Indian Ocean, which trigger eastward-propagating Kelvin waves. Decadal variations of OHC in the western Indian Ocean are linked to conditions in the Pacific via changes in the atmospheric Walker cell, which trigger anomalous wind stress curl and Ekman pumping in the central tropical Indian Ocean. Westward-propagating oceanic Rossby waves extend the influence of this anomalous Ekman pumping to the western Indian Ocean.
    Description: This research was supported by the Independent Research and Development Program at WHOI to CCU, an NSF OCE PO grant (NSF OCE- 1242989) to Young-Oh Kwon, NOAA CP CVP grants (NA15OAR4310176 and NA17OAR4310255) to Hyodae Seo, and a research grant fromtheMinistry of Science and Technology of the People’s Republic of China to Tsinghua University (2017YFA0603902).
    Description: 2019-02-13
    Keywords: Air-sea interaction
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    Dynamics of three-dimensional turbulent wall plumes and implications for estimates of submarine glacier melting (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018):1941-1950, doi:10.1175/JPO-D-17-0194.1.
    Description: Subglacial discharges have been observed to generate buoyant plumes along the ice face of Greenland tidewater glaciers. These plumes have been traditionally modeled using classical plume theory, and their characteristic parameters (e.g., velocity) are employed in the widely used three-equation melt parameterization. However, the applicability of plume theory for three-dimensional turbulent wall plumes is questionable because of the complex near-wall plume dynamics. In this study, corrections to the classical plume theory are introduced to account for the presence of a wall. In particular, the drag and entrainment coefficients are quantified for a three-dimensional turbulent wall plume using data from direct numerical simulations. The drag coefficient is found to be an order of magnitude larger than that for a boundary layer flow over a flat plate at a similar Reynolds number. This result suggests a significant increase in the melting estimates by the current parameterization. However, the volume flux in a wall plume is found to be one-half that of a conical plume that has 2 times the buoyancy flux. This finding suggests that the total entrainment (per unit area) of ambient water is the same and that the plume scalar characteristics (i.e., temperature and salinity) can be predicted reasonably well using classical plume theory.
    Description: This work was supported by the Linné FLOW Centre at KTH and the Academy of Finland Center of Excellence Programme Grant 307331 (author Ezhova) and by VR Swedish Research Council GrantVR2014-5001 (author Brandt). Support to author Cenedese was given by NSF Project OCE-1434041.
    Description: 2019-02-27
    Keywords: Buoyancy ; Entrainment ; Turbulence
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    Some dynamical constraints on upstream pathways of the Denmark Strait Overflow (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 3033–3053, doi:10.1175/JPO-D-13-0227.1.
    Description: The East Greenland Current (EGC) had long been considered the main pathway for the Denmark Strait overflow (DSO). Recent observations, however, indicate that the north Icelandic jet (NIJ), which flows westward along the north coast of Iceland, is a major separate pathway for the DSO. In this study a two-layer numerical model and complementary integral constraints are used to examine various pathways that lead to the DSO and to explore plausible mechanisms for the NIJ’s existence. In these simulations, a westward and NIJ-like current emerges as a robust feature and a main pathway for the Denmark Strait overflow. Its existence can be explained through circulation integrals around advantageous contours. One such constraint spells out the consequences of overflow water as a source of low potential vorticity. A stronger constraint can be added when the outflow occurs through two outlets: it takes the form of a circulation integral around the Iceland–Faroe Ridge. In either case, the direction of overall circulation about the contour can be deduced from the required frictional torques. Some effects of wind stress forcing are also examined. The overall positive curl of the wind forces cyclonic gyres in both layers, enhancing the East Greenland Current. The wind stress forcing weakens but does not eliminate the NIJ. It also modifies the sign of the deep circulation in various subbasins and alters the path by which overflow water is brought to the Faroe Bank Channel, all in ways that bring the idealized model more in line with observations. The sequence of numerical experiments separates the effects of wind and buoyancy forcing and shows how each is important.
    Description: This study has been supported by National Science Foundation (OCE0927017 and ARC1107412).
    Description: 2015-06-01
    Keywords: Circulation/ Dynamics ; Boundary currents ; Channel flows ; Meridional overturning circulation ; Ocean circulation ; Topographic effects
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    Effects of eddy vorticity forcing on the mean state of the Kuroshio Extension (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1356–1375, doi:10.1175/JPO-D-13-0259.1.
    Description: Eddy–mean flow interactions along the Kuroshio Extension (KE) jet are investigated using a vorticity budget of a high-resolution ocean model simulation, averaged over a 13-yr period. The simulation explicitly resolves mesoscale eddies in the KE and is forced with air–sea fluxes representing the years 1995–2007. A mean-eddy decomposition in a jet-following coordinate system removes the variability of the jet path from the eddy components of velocity; thus, eddy kinetic energy in the jet reference frame is substantially lower than in geographic coordinates and exhibits a cross-jet asymmetry that is consistent with the baroclinic instability criterion of the long-term mean field. The vorticity budget is computed in both geographic (i.e., Eulerian) and jet reference frames; the jet frame budget reveals several patterns of eddy forcing that are largely attributed to varicose modes of variability. Eddies tend to diffuse the relative vorticity minima/maxima that flank the jet, removing momentum from the fast-moving jet core and reinforcing the quasi-permanent meridional meanders in the mean jet. A pattern associated with the vertical stretching of relative vorticity in eddies indicates a deceleration (acceleration) of the jet coincident with northward (southward) quasi-permanent meanders. Eddy relative vorticity advection outside of the eastward jet core is balanced mostly by vertical stretching of the mean flow, which through baroclinic adjustment helps to drive the flanking recirculation gyres. The jet frame vorticity budget presents a well-defined picture of eddy activity, illustrating along-jet variations in eddy–mean flow interaction that may have implications for the jet’s dynamics and cross-frontal tracer fluxes.
    Description: A. S. Delman (ASD) and J. L. McClean (JLM) were supported by NSF Grant OCE-0850463 and Office of Science (BER), U.S. Department of Energy, Grant DE-FG02-05ER64119. ASD and J. Sprintall were also supported by a NASA Earth and Space Science Fellowship (NESSF), Grant NNX13AM93H. JLM was also supported by U.S. DOE Office of Science grant entitled “Ultra-High Resolution Global Climate Simulation” via a Los Alamos National Laboratory subcontract. S. R. Jayne was supported by NSF Grant OCE-0849808. Computational resources for the model run were provided by NSF Resource Grants TG-OCE110013 and TG-OCE130010.
    Description: 2015-11-01
    Keywords: Geographic location/entity ; North Pacific Ocean ; Circulation/ Dynamics ; Forcing ; Instability ; Mesoscale processes ; Atm/Ocean Structure/ Phenomena ; Jets ; Models and modeling ; General circulation models
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    Icebergs and sea ice detected with inverted echo sounders (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 32 (2015): 1042–1057, doi:10.1175/JTECH-D-14-00161.1.
    Description: A 1-yr experiment using a pressure-sensor-equipped inverted echo sounder (PIES) was conducted in Sermilik Fjord in southeastern Greenland (66°N, 38°E) from August 2011 to September 2012. Based on these high-latitude data, the interpretation of PIESs’ acoustic travel-time records from regions that are periodically ice covered were refined. In addition, new methods using PIESs for detecting icebergs and sea ice and for estimating iceberg drafts and drift speeds were developed and tested. During winter months, the PIES in Sermilik Fjord logged about 300 iceberg detections and recorded a 2-week period in early March of land-fast ice cover over the instrument site, consistent with satellite synthetic aperture radar (SAR) imagery. The deepest icebergs in the fjord were found to have keel depths greater than approximately 350 m. Average and maximum iceberg speeds were approximately 0.2 and 0.5 m s−1, respectively. The maximum tidal range at the site was ±1.8 m and during neap tides the range was ±0.3 m, as shown by the PIES’s pressure record.
    Description: This work was supported by the National Science Foundation through the Divisions of Ocean Science and Polar Programs under Grant PLR-1332911. A. Silvano was supported as a WHOI guest student through a Gori Fellowship.
    Keywords: Glaciers ; Sea ice ; Ice thickness ; Data processing ; In situ oceanic observations ; Instrumentation/sensors
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    Observations of water mass transformation and eddies in the Lofoten basin of the Nordic Seas (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1735–1756, doi:10.1175/JPO-D-14-0238.1.
    Description: The Lofoten basin of the Nordic Seas is recognized as a crucial component of the meridional overturning circulation in the North Atlantic because of the large horizontal extent of Atlantic Water and winter surface buoyancy loss. In this study, hydrographic and current measurements collected from a mooring deployed in the Lofoten basin from July 2010 to September 2012 are used to describe water mass transformation and the mesoscale eddy field. Winter mixed layer depths (MLDs) are observed to reach approximately 400 m, with larger MLDs and denser properties resulting from the colder 2010 winter. A heat budget of the upper water column requires lateral input, which balances the net annual heat loss of ~80 W m−2. The lateral flux is a result of mesoscale eddies, which dominate the velocity variability. Eddy velocities are enhanced in the upper 1000 m, with a barotropic component that reaches the bottom. Detailed examination of two eddies, from April and August 2012, highlights the variability of the eddy field and eddy properties. Temperature and salinity properties of the April eddy suggest that it originated from the slope current but was ventilated by surface fluxes. The properties within the eddy were similar to those of the mode water, indicating that convection within the eddies may make an important contribution to water mass transformation. A rough estimate of eddy flux per unit boundary current length suggests that fluxes in the Lofoten basin are larger than in the Labrador Sea because of the enhanced boundary current–interior density difference.
    Description: The work was supported by NSF OCE 0850416.
    Description: 2015-12-01
    Keywords: Circulation/ Dynamics ; Atmosphere-ocean interaction ; Boundary currents ; Eddies ; Fluxes ; Mesoscale processes ; Atm/Ocean Structure/ Phenomena ; Thermohaline circulation
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    How climate change affects extremes in maize and wheat yield in two cropping regions (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 4653–4687, doi:10.1175/JCLI-D-13-00326.1.
    Description: Downscaled climate model projections from phase 5 of the Coupled Model Intercomparison Project (CMIP5) were used to force a dynamic vegetation agricultural model (Agro-IBIS) and simulate yield responses to historical climate and two future emissions scenarios for maize in the U.S. Midwest and wheat in southeastern Australia. In addition to mean changes in yield, the frequency of high- and low-yield years was related to changing local hydroclimatic conditions. Particular emphasis was on the seasonal cycle of climatic variables during extreme-yield years and links to crop growth. While historically high (low) yields in Iowa tend to occur during years with anomalous wet (dry) growing season, this is exacerbated in the future. By the end of the twenty-first century, the multimodel mean (MMM) of growing season temperatures in Iowa is projected to increase by more than 5°C, and maize yield is projected to decrease by 18%. For southeastern Australia, the frequency of low-yield years rises dramatically in the twenty-first century because of significant projected drying during the growing season. By the late twenty-first century, MMM growing season precipitation in southeastern Australia is projected to decrease by 15%, temperatures are projected to increase by 2.8°–4.5°C, and wheat yields are projected to decline by 70%. Results highlight the sensitivity of yield projections to the nature of hydroclimatic changes. Where future changes are uncertain, the sign of the yield change simulated by Agro-IBIS is uncertain as well. In contrast, broad agreement in projected drying over southern Australia across models is reflected in consistent yield decreases for the twenty-first century. Climatic changes of the order projected can be expected to pose serious challenges for continued staple grain production in some current centers of production, especially in marginal areas.
    Description: This work was initiated at the Dissertations Initiative for the Advancement of Climate Change Research (DISCCRS) V Symposium, supported by the U.S. National Science Foundation through collaborative Grants SES-0932916 and SES-0931402. CCU was supported by a University of New South Wales Vice-Chancellor Fellowship and the Penzance Endowed Fund and John P. Chase Memorial Endowed Fund at WHOI. TET was supported by the U.S. Department of Energy Award DE-EE0004397. NC was funded by NSF Grant EAR-1204774. We are indebted to the FORMAS-funded Land Use Today and Tomorrow (LUsTT) project (Grant 211-2009-1682) for financial support.
    Keywords: Australia ; North America ; Climate change ; Climate models ; Climate variability ; Agriculture
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    Understanding ENSO diversity (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 96 (2015): 921–938, doi:10.1175/BAMS-D-13-00117.1.
    Description: El Niño–Southern Oscillation (ENSO) is a naturally occurring mode of tropical Pacific variability, with global impacts on society and natural ecosystems. While it has long been known that El Niño events display a diverse range of amplitudes, triggers, spatial patterns, and life cycles, the realization that ENSO’s impacts can be highly sensitive to this event-to-event diversity is driving a renewed interest in the subject. This paper surveys our current state of knowledge of ENSO diversity, identifies key gaps in understanding, and outlines some promising future research directions.
    Description: AC acknowledges support from the National Science Foundation for this study.
    Description: 2015-12-01
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    Spontaneous generation of near-inertial waves by the Kuroshio Front (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2381–2406, doi:10.1175/JPO-D-14-0086.1.
    Description: While near-inertial waves are known to be generated by atmospheric storms, recent observations in the Kuroshio Front find intense near-inertial internal-wave shear along sloping isopycnals, even during calm weather. Recent literature suggests that spontaneous generation of near-inertial waves by frontal instabilities could represent a major sink for the subinertial quasigeostrophic circulation. An unforced three-dimensional 1-km-resolution model, initialized with the observed cross-Kuroshio structure, is used to explore this mechanism. After several weeks, the model exhibits growth of 10–100-km-scale frontal meanders, accompanied by O(10) mW m−2 spontaneous generation of near-inertial waves associated with readjustment of submesoscale fronts forced out of balance by mesoscale confluent flows. These waves have properties resembling those in the observations. However, they are reabsorbed into the model Kuroshio Front with no more than 15% dissipating or radiating away. Thus, spontaneous generation of near-inertial waves represents a redistribution of quasigeostrophic energy rather than a significant sink.
    Description: “The Study of Kuroshio Ecosystem Dynamics for Sustainable Fisheries (SKED)” supported by MEXT, MIT-Hayashi Seed Fund, ONR (Awards N000140910196 and N000141210101), NSF (Award OCE 0928617, 0928138) for support.
    Description: 2016-03-01
    Keywords: Circulation/ Dynamics ; Frontogenesis/frontolysis ; Fronts ; Internal waves ; Turbulence ; Upwelling/downwelling ; Atm/Ocean Structure/ Phenomena ; Jets
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    Wintertime atmospheric response to North Atlantic Ocean circulation variability in a climate model (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 28 (2015): 7659–7677, doi:10.1175/JCLI-D-15-0007.1.
    Description: Maximum covariance analysis of a preindustrial control simulation of the NCAR Community Climate System Model, version 4 (CCSM4), shows that a barotropic signal in winter broadly resembling a negative phase of the North Atlantic Oscillation (NAO) follows an intensification of the Atlantic meridional overturning circulation (AMOC) by about 7 yr. The delay is due to the cyclonic propagation along the North Atlantic Current (NAC) and the subpolar gyre of a SST warming linked to a northward shift and intensification of the NAC, together with an increasing SST cooling linked to increasing southward advection of subpolar water along the western boundary and a southward shift of the Gulf Stream (GS). These changes result in a meridional SST dipole, which follows the AMOC intensification after 6 or 7 yr. The SST changes were initiated by the strengthening of the western subpolar gyre and by bottom torque at the crossover of the deep branches of the AMOC with the NAC on the western flank of the Mid-Atlantic Ridge and the GS near the Tail of the Grand Banks, respectively. The heat flux damping of the SST dipole shifts the region of maximum atmospheric transient eddy growth southward, leading to a negative NAO-like response. No significant atmospheric response is found to the Atlantic multidecadal oscillation (AMO), which is broadly realistic but shifted south and associated with a much weaker meridional SST gradient than the AMOC fingerprint. Nonetheless, the wintertime atmospheric response to the AMOC shows some similarity with the observed response to the AMO, suggesting that the ocean–atmosphere interactions are broadly realistic in CCSM4.
    Description: Support from the NOAA Climate Program Office (NA10OAR4310202 and NA13OAR4310139), NSF EaSM2 (OCE 1242989) and the European Community 7th framework programme (FP7 2007-2013) under Grant Agreement 308299 (NACLIM) is gratefully acknowledged. The analysis benefited from the IPSL Prodiguer-Ciclad facility, which is supported by CNRS, UPMC, Labex L-IPSL funded by the ANR (Grant ANR-10-LABX-0018) and by the European FP7 IS-ENES2 project (Grant 312979).
    Description: 2016-04-01
    Keywords: Meridional overturning circulation ; North Atlantic Oscillation ; Climate models ; Climate variability
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    Lidar and pressure measurements of inner-surfzone waves and setup (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 32 (2015): 1945–1959, doi:10.1175/JTECH-D-14-00222.1.
    Description: Observations of waves and setup on a steep, sandy beach are used to identify and assess potential applications of spatially dense lidar measurements for studying inner-surf and swash-zone hydrodynamics. There is good agreement between lidar- and pressure-based estimates of water levels (r2 = 0.98, rmse = 0.05 m), setup (r2 = 0.92, rmse = 0.03 m), infragravity wave heights (r2 = 0.91, rmse = 0.03 m), swell–sea wave heights (r2 = 0.87, rmse = 0.07 m), and energy density spectra. Lidar observations did not degrade with range (up to 65 m offshore of the lidar) when there was sufficient foam present on the water surface to generate returns, suggesting that for narrow-beam 1550-nm light, spatially varying spot size, grazing angle affects, and linear interpolation (to estimate the water surface over areas without returns) are not large sources of error. Consistent with prior studies, the lidar and pressure observations indicate that standing infragravity waves dominate inner-surf and swash energy at low frequencies and progressive swell–sea waves dominate at higher frequencies. The spatially dense lidar measurements enable estimates of reflection coefficients from pairs of locations at a range of spatial lags (thus spanning a wide range of frequencies or wavelengths). Reflection is high at low frequencies, increases with beach slope, and decreases with increasing offshore wave height, consistent with prior studies. Lidar data also indicate that wave asymmetry increases rapidly across the inner surf and swash. The comparisons with pressure measurements and with theory demonstrate that lidar measures inner-surf waves and setup accurately, and can be used for studies of inner-surf and swash-zone hydrodynamics.
    Description: Funding was provided by the USACE Coastal Field Data Collection (CFDC) and Coastal Ocean Data Systems (CODS) programs, the Office of Naval Research, the National Science Foundation, and the Assistant Secretary of Defense (R&E).
    Description: 2016-04-01
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    Biases in Thorpe-scale estimates of turbulence dissipation. Part I : Assessments from large-scale overturns in oceanographic data (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2497–2521, doi:10.1175/JPO-D-14-0128.1.
    Description: Oceanic density overturns are commonly used to parameterize the dissipation rate of turbulent kinetic energy. This method assumes a linear scaling between the Thorpe length scale LT and the Ozmidov length scale LO. Historic evidence supporting LT ~ LO has been shown for relatively weak shear-driven turbulence of the thermocline; however, little support for the method exists in regions of turbulence driven by the convective collapse of topographically influenced overturns that are large by open-ocean standards. This study presents a direct comparison of LT and LO, using vertical profiles of temperature and microstructure shear collected in the Luzon Strait—a site characterized by topographically influenced overturns up to O(100) m in scale. The comparison is also done for open-ocean sites in the Brazil basin and North Atlantic where overturns are generally smaller and due to different processes. A key result is that LT/LO increases with overturn size in a fashion similar to that observed in numerical studies of Kelvin–Helmholtz (K–H) instabilities for all sites but is most clear in data from the Luzon Strait. Resultant bias in parameterized dissipation is mitigated by ensemble averaging; however, a positive bias appears when instantaneous observations are depth and time integrated. For a series of profiles taken during a spring tidal period in the Luzon Strait, the integrated value is nearly an order of magnitude larger than that based on the microstructure observations. Physical arguments supporting LT ~ LO are revisited, and conceptual regimes explaining the relationship between LT/LO and a nondimensional overturn size are proposed. In a companion paper, Scotti obtains similar conclusions from energetics arguments and simulations.
    Description: B.D.M. and S.K.V. gratefully acknowledge the support of the Office of Naval Research under Grants N00014-12-1-0279, N00014-12-1-0282, and N00014-12-1-0938 (Program Manager: Dr. Terri Paluszkiewicz). S.K.V. also acknowledges support of the National Science Foundation under Grant OCE-1151838. L.S.L. acknowledges support for BBTRE by the National Science Foundation by Contract OCE94-15589 and NATRE and IWISE by the Office of Naval Research by Contracts N00014-92-1323 and N00014-10-10315. J.N.M. was supported through Grant 1256620 from the National Science Foundation and the Office of Naval Research (IWISE Project).
    Description: 2016-04-01
    Keywords: Circulation/ Dynamics ; Diapycnal mixing ; Small scale processes ; Turbulence ; Atm/Ocean Structure/ Phenomena ; Mixing ; Observational techniques and algorithms ; Profilers, oceanic ; Models and modeling ; Parameterization
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    Characterization and modulation of Langmuir circulation in Chesapeake Bay (2015)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2621–2639, doi:10.1175/JPO-D-14-0239.1.
    Description: Measurements made as part of a large-scale experiment to examine wind-driven circulation and mixing in Chesapeake Bay demonstrate that circulations consistent with Langmuir circulation play an important role in surface boundary layer dynamics. Under conditions when the turbulent Langmuir number Lat is low (〈0.5), the surface mixed layer is characterized by 1) elevated vertical turbulent kinetic energy; 2) decreased anisotropy; 3) negative vertical velocity skewness indicative of strong/narrow downwelling and weak/broad upwelling; and 4) strong negative correlations between low-frequency vertical velocity and the velocity in the direction of wave propagation. These characteristics appear to be primarily the result of the vortex force associated with the surface wave field, but convection driven by a destabilizing heat flux is observed and appears to contribute significantly to the observed negative vertical velocity skewness. Conditions that favor convection usually also have strong Langmuir forcing, and these two processes probably both contribute to the surface mixed layer turbulence. Conditions in which traditional stress-driven turbulence is important are limited in this dataset. Unlike other shallow coastal systems where full water column Langmuir circulation has been observed, the salinity stratification in Chesapeake Bay is nearly always strong enough to prevent full-depth circulation from developing.
    Description: The funding for this research was provided by the National Science Foundation Grants OCE-1339032 and OCE-1338518.
    Description: 2016-04-01
    Keywords: Circulation/ Dynamics ; Convection ; Instability ; Mixing ; Turbulence ; Wave breaking ; Wind stress
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    The annual cycle of the Japan Sea throughflow (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 23–39, doi:10.1175/JPO-D-15-0075.1.
    Description: The mechanism responsible for the annual cycle of the flow through the straits of the Japan Sea is investigated using a two-layer model. Observations show maximum throughflow from summer to fall and minimum in winter, occurring synchronously at the three major straits: Tsushima, Tsugaru, and Soya Straits. This study finds the subpolar winds located to the north of Japan as the leading forcing agent, which first affects the Soya Strait rather than the Tsushima or Tsugaru Straits. The subpolar winds generate baroclinic Kelvin waves along the coastlines of the subpolar gyre, affect the sea surface height at the Soya Strait, and modify the flow through the strait. This causes barotropic adjustment to occur inside the Japan Sea and thus affect the flow at the Tsugaru and Tsushima Straits almost synchronously. The barotropic adjustment mechanism explains well why the observations show a similar annual cycle at the three straits. The annual cycle at the Tsugaru Strait is further shown to be weaker than that in the other two straits based on frictional balance around islands, that is, frictional stresses exerted around an island integrate to zero. In the Tsugaru Strait, the flows induced by the frictional integrals around the northern (Hokkaido) and southern (Honshu) islands are in opposite directions and tend to cancel out. Frictional balance also suggests that the annual cycle at the Tsugaru Strait is likely in phase with that at the Soya Strait because the length scale of the northern island is much shorter than that of the southern island.
    Description: S. Kida is supported by KAKENHI (22106002). B. Qiu is supported by NASA (NNX13AE15G). J. Yang is supported by the U.S. National Science Foundation. X. Lin is supported by the Natural Science Foundation of China (41222037 and U1406401), China’s National Basic Research Priorities Programme (2013CB956202), and the Global Air-Sea Interaction Project (GASI-03-01-01-02).
    Description: 2016-07-01
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    Tidal mixing in the South China Sea : an estimate based on the internal tide energetics (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 107–124, doi:10.1175/JPO-D-15-0082.1.
    Description: By taking into account the contributions of both locally and remotely generated internal tides, the tidal mixing in the Luzon Strait (LS) and the South China Sea (SCS) is investigated through internal-tide simulation and energetics analysis. A three-dimensional nonhydrostatic high-resolution model driven by four primary tidal constituents (M2, S2, K1, and O1) is used for the internal-tide simulation. The baroclinic energy budget analysis reveals that the internal tides radiated from the LS are the dominant energy source for the tidal dissipation in the SCS. In the LS, the estimated depth-integrated turbulent kinetic energy dissipation exceeds O(1) W m−2 atop the two subsurface ridges, with a dissipation rate of 〉O(10−7) W kg−1 and diapycnal diffusivity of ~O(10−2) m2 s−1. In the SCS, the most intense turbulence occurs in the deep-water basin with a dissipation rate of O(10−8–10−6) W kg−1 and diapycnal diffusivity of O(10−3–10−1) m2 s−1 within the ~2000-m water column above the seafloor as well as in the shelfbreak region with a dissipation rate of O(10−7–10−6) W kg−1 and diapycnal diffusivity of O(10−4–10−3) m2 s−1. These estimated values are consistent with observations reported in previous studies and are at least one order of magnitude larger than those based solely on locally generated internal tides.
    Description: This work is jointly supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11010304, XDA11010204), the MOST of China (2014CB953904), the Knowledge Innovation Program of the Chinese Academy of Sciences (SQ201305), and National Natural Science Foundation of China (41376021, 41306013). ZL’s participation of this work was supported by the National Natural Science Foundation of China (41476006), the Natural Science Foundation of Fujian Province of China (2015J06010), and the National Basic Research Program of China (2012CB417402).
    Description: 2016-07-01
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    A microscale view of mixing and overturning across the Antarctic Circumpolar Current (2016)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 233–254, doi:10.1175/JPO-D-15-0025.1.
    Description: The relative roles of isoneutral stirring by mesoscale eddies and dianeutral stirring by small-scale turbulence in setting the large-scale temperature–salinity relation of the Southern Ocean against the action of the overturning circulation are assessed by analyzing a set of shear and temperature microstructure measurements across Drake Passage in a “triple decomposition” framework. It is shown that a picture of mixing and overturning across a region of the Antarctic Circumpolar Current (ACC) may be constructed from a relatively modest number of microstructure profiles. The rates of isoneutral and dianeutral stirring are found to exhibit distinct, characteristic, and abrupt variations: most notably, a one to two orders of magnitude suppression of isoneutral stirring in the upper kilometer of the ACC frontal jets and an order of magnitude intensification of dianeutral stirring in the subpycnocline and deepest layers of the ACC. These variations balance an overturning circulation with meridional flows of O(1) mm s−1 across the ACC’s mean thermohaline structure. Isoneutral and dianeutral stirring play complementary roles in balancing the overturning, with isoneutral processes dominating in intermediate waters and the Upper Circumpolar Deep Water and dianeutral processes prevailing in lighter and denser layers.
    Description: The DIMES experiment was funded by the U.K. Natural Environment Research Council (NERC) and the U.S. National Science Foundation (NSF). ACNG acknowledges the support of a Philip Leverhulme Prize, the Royal Society, and the Wolfson Foundation. JDZ acknowledges the support of a NERC Research Fellowship.
    Description: 2016-07-01
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    Impact of a localized source of subglacial discharge on the heat flux and submarine melting of a tidewater glacier : a laboratory study (2016)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3155-3163, doi:10.1175/JPO-D-16-0123.1.
    Description: Idealized laboratory experiments have been conducted in a two-layer stratified fluid to investigate the leading-order dynamics that control submarine melting and meltwater export near a vertical ice–ocean interface as a function of subglacial discharge. In summer, the discharge of surface runoff at the base of a glacier (subglacial discharge) generates strong buoyant plumes that rise along the glacier front entraining ambient water along the way. The entrainment enhances the heat transport toward the glacier front and hence the submarine melt rate increases with the subglacial discharge rate. In the laboratory, the effect of subglacial discharge is simulated by introducing freshwater at freezing temperature from a point source at the base of an ice block representing the glacier. The circulation pattern observed both with and without subglacial discharge resembles those observed in previous observational and numerical studies. Buoyant plumes rise vertically until they find either their neutrally buoyant level or the free surface. Hence, the meltwater can deposit within the interior of the water column and not entirely at the free surface, as confirmed by field observations. The heat budget in the tank, calculated following a new framework, gives estimates of submarine melt rate that increase with the subglacial discharge and are in agreement with the directly measured submarine melting. This laboratory study provides the first direct measurements of submarine melt rates for different subglacial discharges, and the results are consistent with the predictions of previous theoretical and numerical studies.
    Description: Support to C. C. was given by the NSF project OCE- 1130008 and OCE-1434041. M. G. received support from the ‘‘Gori’’ Fellowship.
    Description: 2017-04-07
    Keywords: Glaciers ; Buoyancy ; Density currents ; Turbulence ; Laboratory/physical models
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    Satellite and in situ salinity : understanding near-surface stratification and subfootprint variability (2016)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 97 (2016): 1391-1407, doi:10.1175/BAMS-D-15-00032.1.
    Description: Remote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top few centimeters of the ocean, whereas most in situ observations are reported below a depth of a few meters. Additionally, satellites measure salinity as a spatial average over an area of about 100 × 100 km2. In contrast, in situ sensors provide pointwise measurements at the location of the sensor. Thus, the presence of vertical gradients in, and horizontal variability of, sea surface salinity complicates comparison of satellite and in situ measurements. This paper synthesizes present knowledge of the magnitude and the processes that contribute to the formation and evolution of vertical and horizontal variability in near-surface salinity. Rainfall, freshwater plumes, and evaporation can generate vertical gradients of salinity, and in some cases these gradients can be large enough to affect validation of satellite measurements. Similarly, mesoscale to submesoscale processes can lead to horizontal variability that can also affect comparisons of satellite data to in situ data. Comparisons between satellite and in situ salinity measurements must take into account both vertical stratification and horizontal variability.
    Description: 2017-02-28
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    Can Australian multiyear droughts and wet spells be generated in the absence of oceanic variability? (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 29 (2016): 6201-6221, doi:10.1175/JCLI-D-15-0694.1.
    Description: Anomalous conditions in the tropical oceans, such as those related to El Niño–Southern Oscillation and the Indian Ocean dipole, have been previously blamed for extended droughts and wet periods in Australia. Yet the extent to which Australian wet and dry spells can be driven by internal atmospheric variability remains unclear. Natural variability experiments are examined to determine whether prolonged extreme wet and dry periods can arise from internal atmospheric and land variability alone. Results reveal that this is indeed the case; however, these dry and wet events are found to be less severe than in simulations incorporating coupled oceanic variability. Overall, ocean feedback processes increase the magnitude of Australian rainfall variability by about 30% and give rise to more spatially coherent rainfall impacts. Over mainland Australia, ocean interactions lead to more frequent extreme events, particularly during the rainy season. Over Tasmania, in contrast, ocean–atmosphere coupling increases mean rainfall throughout the year. While ocean variability makes Australian rainfall anomalies more severe, droughts and wet spells of duration longer than three years are equally likely to occur in both atmospheric- and ocean-driven simulations. Moreover, they are essentially indistinguishable from what one expects from a Gaussian white noise distribution. Internal atmosphere–land-driven megadroughts and megapluvials that last as long as ocean-driven events are also identified in the simulations. This suggests that oceanic variability may be less important than previously assumed for the long-term persistence of Australian rainfall anomalies. This poses a challenge to accurate prediction of long-term dry and wet spells for Australia.
    Description: This study was supported by the Australian Research Council (ARC) under ARC-DP1094784, ARC-DP-150101331, ARC-FL100100214, and funding for C.C.U. from the National Science Foundation under AGS-1602455 and the ARC Centre of Excellence for Climate System Science.
    Description: 2017-02-19
    Keywords: Circulation/ Dynamics ; Atmosphere-ocean interaction ; Atm/Ocean Structure/ Phenomena ; Drought ; Precipitation ; Physical Meteorology and Climatology ; Climate variability ; Forecasting ; Climate prediction ; Variability
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    A theory of the wind-driven Beaufort Gyre variability (2016)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3263-3278, doi:10.1175/JPO-D-16-0091.1.
    Description: The halocline of the Beaufort Gyre varies significantly on interannual to decadal time scales, affecting the freshwater content (FWC) of the Arctic Ocean. This study explores the role of eddies in the Ekman-driven gyre variability. Following the transformed Eulerian-mean paradigm, the authors develop a theory that links the FWC variability to the stability of the large-scale gyre, defined as the inverse of its equilibration time. The theory, verified with eddy-resolving numerical simulations, demonstrates that the gyre stability is explicitly controlled by the mesoscale eddy diffusivity. An accurate representation of the halocline dynamics requires the eddy diffusivity of 300 ± 200 m2 s−1, which is lower than what is used in most low-resolution climate models. In particular, on interannual and longer time scales the eddy fluxes and the Ekman pumping provide equally important contributions to the FWC variability. However, only large-scale Ekman pumping patterns can significantly alter the FWC, with spatially localized perturbations being an order of magnitude less efficient. Lastly, the authors introduce a novel FWC tendency diagnostic—the Gyre Index—that can be conveniently calculated using observations located only along the gyre boundaries. Its strong predictive capabilities, assessed in the eddy-resolving model forced by stochastic winds, suggest that the Gyre Index would be of use in interpreting FWC evolution in observations as well as in numerical models.
    Description: GEMacknowledges the support from theHowland Postdoctoral Program Fund at WHOI and the Stanback Fellowship Fund at Caltech.MAS was supported by NSF Grants PLR-1415489 and OCE-1232389. AFT acknowledges support from NASA Award NNN12AA01C.
    Description: 2017-04-20
    Keywords: Arctic ; Eddies ; Ekman pumping/transport ; Large-scale motions ; Ocean circulation ; Stability
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    Coral reef drag coefficients – water depth dependence (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 1061-1075, doi:10.1175/JPO-D-16-0248.1.
    Description: A major challenge in modeling the circulation over coral reefs is uncertainty in the drag coefficient because existing estimates span two orders of magnitude. Current and pressure measurements from five coral reefs are used to estimate drag coefficients based on depth-average flow, assuming a balance between the cross-reef pressure gradient and the bottom stress. At two sites wind stress is a significant term in the cross-reef momentum balance and is included in estimating the drag coefficient. For the five coral reef sites and a previous laboratory study, estimated drag coefficients increase as the water depth decreases consistent with open channel flow theory. For example, for a typical coral reef hydrodynamic roughness of 5 cm, observational estimates, and the theory indicate that the drag coefficient decreases from 0.4 in 20 cm of water to 0.005 in 10 m of water. Synthesis of results from the new field observations with estimates from previous field and laboratory studies indicate that coral reef drag coefficients range from 0.2 to 0.005 and hydrodynamic roughnesses generally range from 2 to 8 cm. While coral reef drag coefficients depend on factors such as physical roughness and surface waves, a substantial fraction of the scatter in estimates of coral reef drag coefficients is due to variations in water depth.
    Description: The Red Sea field program was supported by Awards USA 00002 and KSA 00011 made by KAUST to S. Lentz and J. Churchill. The Palau field program was funded by NSF Award OCE-1220529.
    Keywords: Ocean ; Currents ; Wind stress ; Boundary layer ; Sea level ; Tides
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    Generation of internal solitary waves by lateral circulation in a stratified estuary (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 1789-1797, doi:10.1175/JPO-D-16-0240.1.
    Description: Internal solitary waves are commonly observed in the coastal ocean where they are known to contribute to mass transport and turbulent mixing. While these waves are often generated by cross-isobath barotropic tidal currents, novel observations are presented suggesting that internal solitary waves result from along-isobath tidal flows over channel-shoal bathymetry. Mooring and ship-based velocity, temperature, and salinity data were collected over a cross-channel section in a stratified estuary. The data show that Ekman forcing on along-channel tidal currents drives lateral circulation, which interacts with the stratified water over the deep channel to generate a supercritical mode-2 internal lee wave. This lee wave propagates onto the shallow shoal and evolves into a group of internal solitary waves of elevation due to nonlinear steepening. These observations highlight the potential importance of three-dimensionality on the conversion of tidal flow to internal waves in the rotating ocean.
    Description: National Science Foundation (OCE-1061609)
    Description: 2018-01-03
    Keywords: Estuaries ; Internal waves ; Solitary waves
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    Distinct influence of air–sea interactions mediated by mesoscale sea surface temperature and surface current in the Arabian Sea (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2017): 8061-8080, doi:10.1175/JCLI-D-16-0834.1.
    Description: During the southwest monsoons, the Arabian Sea (AS) develops highly energetic mesoscale variability associated with the Somali Current (SC), Great Whirl (GW), and cold filaments (CF). The resultant high-amplitude anomalies and gradients of sea surface temperature (SST) and surface currents modify the wind stress, triggering the so-called mesoscale coupled feedbacks. This study uses a high-resolution regional coupled model with a novel coupling procedure that separates spatial scales of the air–sea coupling to show that SST and surface currents are coupled to the atmosphere at distinct spatial scales, exerting distinct dynamic influences. The effect of mesoscale SST–wind interaction is manifested most strongly in wind work and Ekman pumping over the GW, primarily affecting the position of GW and the separation latitude of the SC. If this effect is suppressed, enhanced wind work and a weakened Ekman pumping dipole cause the GW to extend northeastward, delaying the SC separation by 1°. Current–wind interaction, in contrast, is related to the amount of wind energy input. When it is suppressed, especially as a result of background-scale currents, depth-integrated kinetic energy, both the mean and eddy, is significantly enhanced. Ekman pumping velocity over the GW is overly negative because of a lack of vorticity that offsets the wind stress curl, further invigorating the GW. Moreover, significant changes in time-mean SST and evaporation are generated in response to the current–wind interaction, accompanied by a noticeable southward shift in the Findlater Jet. The significant increase in moisture transport in the central AS implies that air–sea interaction mediated by the surface current is a potentially important process for simulation and prediction of the monsoon rainfall.
    Description: This work is supported by ONR (N00014-15-1-2588 and N00014-17-1-2398), NSF (OCE- 1419235), and NOAA (NA15OAR4310176).
    Description: 2018-03-08
    Keywords: Indian Ocean ; Wind stress ; Ekman pumping ; Monsoons ; Air-sea interaction ; Coupled models
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    Thermocline fluctuations in the equatorial Pacific related to the two types of El Niño events (2017)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 30 (2017): 6611-6627, doi:10.1175/JCLI-D-16-0291.1.
    Description: The interannual fluctuations of the equatorial thermocline are usually associated with El Niño activity, but the linkage between the thermocline modes and El Niño is still under debate. In the present study, a mode function decomposition method is applied to the equatorial Pacific thermocline, and the results show that the first two dominant modes (M1 and M2) identify two distinct characteristics of the equatorial Pacific thermocline. The M1 reflects a basinwide zonally tilted thermocline related to the eastern Pacific (EP) El Niño, with shoaling (deepening) in the western (eastern) equatorial Pacific. The M2 represents the central Pacific (CP) El Niño, characterized by a V-shaped equatorial Pacific thermocline (i.e., deep in the central equatorial Pacific and shallow on both the western and eastern boundaries). Furthermore, both modes are stable and significant on the interannual time scale, and manifest as the major feature of the thermocline fluctuations associated with the two types of El Niño events. As good proxies of EP and CP El Niño events, thermocline-based indices clearly reveal the inherent characteristics of subsurface ocean responses during the evolution of El Niño events, which are characterized by the remarkable zonal eastward propagation of equatorial subsurface ocean temperature anomalies, particularly during the CP El Niño. Further analysis of the mixed layer heat budget suggests that the air–sea interactions determine the establishment and development stages of the CP El Niño, while the thermocline feedback is vital for its further development. These results highlight the key influence of equatorial Pacific thermocline fluctuations in conjunction with the air–sea interactions, on the CP El Niño.
    Description: This work is jointly supported by the Funds for Creative Research Groups of China (Grant 41521005), the Special Fund for Public Welfare Industry (GYHY201506013), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDA11010301), and the National Natural Science Foundation of China (Grants 41406033, 41475057, 41376024, 41676013) and the CAS/SAFEA International Partnership Program for Creative Research Teams.
    Description: 2018-01-21
    Keywords: Thermocline ; El Nino
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    Dominant circulation patterns of the deep Gulf of Mexico (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 511-529, doi:10.1175/JPO-D-17-0140.1.
    Description: The large-scale circulation of the bottom layer of the Gulf of Mexico is analyzed, with special attention to the historically least studied western basin. The analysis is based on 4 years of data collected by 158 subsurface floats parked at 1500 and 2500 m and is complemented with data collected by current meter moorings in the western basin during the same period. Three main circulation patterns stand out: a cyclonic boundary current, a cyclonic gyre in the abyssal plain, and the very high eddy kinetic energy observed in the eastern Gulf. The boundary current and the cyclonic gyre appear as distinct features, which interact in the western tip of the Yucatan shelf. The persistence and continuity of the boundary current is addressed. Although high variability is observed, the boundary flow serves as a pathway for water to travel around the western basin in approximately 2 years. An interesting discovery is the separation of the boundary current over the northwestern slope of the Yucatan shelf. The separation and retroflection of the along-slope current appears to be a persistent feature and is associated with anticyclonic eddies whose genesis mechanism remains to be understood. As the boundary flow separates, it feeds into the westward flow of the deep cyclonic gyre. The location of this gyre—named the Sigsbee Abyssal Gyre—coincides with closed geostrophic contours, so eddy–topography interaction via bottom form stresses may drive this mean flow. The contribution to the cyclonic vorticity of the gyre by modons traveling under Loop Current eddies is discussed.
    Description: This work was supported by the Bureau of Ocean Energy Management (BOEM) under Contract M10PC00112 assigned to Leidos, Inc.
    Keywords: Seas/gulfs/bays ; Abyssal circulation ; Boundary currents ; Lagrangian circulation/transport ; Large-scale motions ; Trajectories
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    Influences of Pacific climate variability on decadal subsurface ocean heat content variations in the Indian Ocean (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 4157-4174, doi:10.1175/JCLI-D-17-0654.1.
    Description: Decadal variabilities in Indian Ocean subsurface ocean heat content (OHC; 50–300 m) since the 1950s are examined using ocean reanalyses. This study elaborates on how Pacific variability modulates the Indian Ocean on decadal time scales through both oceanic and atmospheric pathways. High correlations between OHC and thermocline depth variations across the entire Indian Ocean Basin suggest that OHC variability is primarily driven by thermocline fluctuations. The spatial pattern of the leading mode of decadal Indian Ocean OHC variability closely matches the regression pattern of OHC on the interdecadal Pacific oscillation (IPO), emphasizing the role of the Pacific Ocean in determining Indian Ocean OHC decadal variability. Further analyses identify different mechanisms by which the Pacific influences the eastern and western Indian Ocean. IPO-related anomalies from the Pacific propagate mainly through oceanic pathways in the Maritime Continent to impact the eastern Indian Ocean. By contrast, in the western Indian Ocean, the IPO induces wind-driven Ekman pumping in the central Indian Ocean via the atmospheric bridge, which in turn modifies conditions in the southwestern Indian Ocean via westward-propagating Rossby waves. To confirm this, a linear Rossby wave model is forced with wind stresses and eastern boundary conditions based on reanalyses. This linear model skillfully reproduces observed sea surface height anomalies and highlights both the oceanic connection in the eastern Indian Ocean and the role of wind-driven Ekman pumping in the west. These findings are also reproduced by OGCM hindcast experiments forced by interannual atmospheric boundary conditions applied only over the Pacific and Indian Oceans, respectively.
    Description: This research was supported by a scholarship from the China Scholarship Council (CSC) to X. J., a research fellowship by the Alexander von Humboldt Foundation to C. C. U., an NSF OCE PO Grant (OCE- 1242989) to Y.-O. K., the ONR Young Investigator Award (N00014-15-1-2588) to H. S., and a research grant from the Ministry of Science and Technology of the People’s Republic of China to Tsinghua University (2017YFA0603902).
    Description: 2018-10-30
    Keywords: Atmosphere-ocean interaction
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    A multivariate estimate of the cold season atmospheric response to North Pacific SST variability (2018)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 2771-2796, doi:10.1175/JCLI-D-17-0061.1.
    Description: The Generalized Equilibrium Feedback Analysis (GEFA) is used to distinguish the influence of the Oyashio Extension (OE) and the Kuroshio Extension (KE) variability on the atmosphere from 1979 to 2014 from that of the main SST variability modes, using seasonal mean anomalies. Remote SST anomalies are associated with each single oceanic regressor, but the multivariate approach efficiently confines their SST footprints. In autumn [October–December (OND)], the OE meridional shifts are followed by a North Pacific Oscillation (NPO)-like signal. The OE influence is not investigated in winter [December–February (DJF)] because of multicollinearity, but a robust response with a strong signal over the Bering Sea is found in late winter/early spring [February–April (FMA)], a northeastward strengthening of the Aleutian low following a northward OE shift. A robust response to the KE variability is found in autumn, but not in winter and late winter when the KE SST footprint becomes increasingly small and noisy as regressors are added in GEFA. In autumn, a positive PDO is followed by a northward strengthening of the Aleutian low and a southward shift of the storm track in the central Pacific, reflecting the surface heat flux footprint in the central Pacific. In winter, the PDO shifts the maximum baroclinicity and storm track southward, the response strongly tilts westward with height in the North Pacific, and there is a negative NAO-like teleconnection. In late winter, the North Pacific NPO-like response to the PDO interferes negatively with the response to the OE and is only detected when the OE is represented in GEFA. A different PDO influence on the atmospheric circulation is found from 1958 to 1977.
    Description: This research has received funding from the European Union 7th Framework Program (FP7 2007-2013) under Grant Agreement 308299 (NACLIM) and from NSF Grants AGS CLD 1035423 and OCE PO 1242989.
    Keywords: Atmosphere-ocean interaction ; Boundary currents ; Pacific decadal oscillation ; Atmosphere-ocean interaction ; Empirical orthogonal functions ; Regression analysis
    Repository Name: Woods Hole Open Access Server
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  • 155
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    A laboratory study of iceberg side melting in vertically sheared flows (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1367-1373, doi:10.1175/JPO-D-17-0185.1.
    Description: An earlier study indicates that the side melting of icebergs subject to vertically homogeneous horizontal velocities is controlled by two distinct regimes, which depend on the melt plume behavior and produce a nonlinear dependence of side melt rate on velocity. Here, we extend this study to consider ice blocks melting in a two-layer vertically sheared flow in a laboratory setting. It is found that the use of the vertically averaged flow speed in current melt parameterizations gives an underestimate of the submarine side melt rate, in part because of the nonlinearity of the dependence of the side melt rate on flow speed but also because vertical shear in the horizontal velocity profile fundamentally changes the flow splitting around the ice block and consequently the velocity felt by the ice surface. An observational record of 90 icebergs in a Greenland fjord suggests that this effect could produce an average underestimate of iceberg side melt rates of 21%.
    Description: A. F. was supported by NA14OAR4320106 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce. C. C. was supported by NSF OCE-1658079 and F. S. was supported by NSF OCE-1657601 and NSF PLR-1743693.
    Description: 2018-12-12
    Keywords: Ocean ; Antarctica ; Arctic ; Laboratory/physical models ; Parameterization
    Repository Name: Woods Hole Open Access Server
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  • 156
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    A global glacial ocean state estimate constrained by upper-ocean temperature proxies (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 8059-8079, doi:10.1175/JCLI-D-17-0769.1.
    Description: We use the method of least squares with Lagrange multipliers to fit an ocean general circulation model to the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) estimate of near sea surface temperature (NSST) at the Last Glacial Maximum (LGM; circa 23–19 thousand years ago). Compared to a modern simulation, the resulting global, last-glacial ocean state estimate, which fits the MARGO data within uncertainties in a free-running coupled ocean–sea ice simulation, has global-mean NSSTs that are 2°C lower and greater sea ice extent in all seasons in both the Northern and Southern Hemispheres. Increased brine rejection by sea ice formation in the Southern Ocean contributes to a stronger abyssal stratification set principally by salinity, qualitatively consistent with pore fluid measurements. The upper cell of the glacial Atlantic overturning circulation is deeper and stronger. Dye release experiments show similar distributions of Southern Ocean source waters in the glacial and modern western Atlantic, suggesting that LGM NSST data do not require a major reorganization of abyssal water masses. Outstanding challenges in reconstructing LGM ocean conditions include reducing effects from model biases and finding computationally efficient ways to incorporate abyssal tracers in global circulation inversions. Progress will be aided by the development of coupled ocean–atmosphere–ice inverse models, by improving high-latitude model processes that connect the upper and abyssal oceans, and by the collection of additional paleoclimate observations.
    Description: DEA was supported by a NSF Graduate Research Fellowship and NSF Grant OCE-1060735. OM acknowledges support from the NSF. GF was supported by NASA Award 1553749 and Simons Foundation Award 549931.
    Keywords: Ocean ; Abyssal circulation ; Sea surface temperature ; Paleoclimate ; Inverse methods ; Ocean models
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  • 157
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    Internal tidal modal ray refraction and energy ducting in baroclinic Gulf Stream currents (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1969-1993, doi:10.1175/JPO-D-18-0031.1.
    Description: Upstream mean semidiurnal internal tidal energy flux has been found in the Gulf Stream in hydrodynamical model simulations of the Atlantic Ocean. A major source of the energy in the simulations is the south edge of Georges Bank, where strong and resonant Gulf of Maine tidal currents are found. An explanation of the flux pattern within the Gulf Stream is that internal wave modal rays can be strongly redirected by baroclinic currents and even trapped (ducted) by current jets that feature strong velocities above the thermocline that are directed counter to the modal wavenumber vector (i.e., when the waves travel upstream). This ducting behavior is analyzed and explained here with ray-based wave propagation studies for internal wave modes with anisotropic wavenumbers, as occur in mesoscale background flow fields. Two primary analysis tools are introduced and then used to analyze the strong refraction and ducting: the generalized Jones equation governing modal properties and ray equations that are suitable for studying waves with anisotropic wavenumbers.
    Description: The Woods Hole research was supported by National Science Foundation Grant OCE-1060430 and by the Office of Naval Research Grants N00014-11-1-0701 and N00014-17-1-2624. The USM research was supported by ONR Grant N00014-15-1-2288 and National Science Foundation Grant OCE-1537449.
    Description: 2019-02-28
    Keywords: Internal waves ; Wave properties ; Tides ; Differential equations ; Numerical analysis/modeling
    Repository Name: Woods Hole Open Access Server
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  • 158
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    Estuarine exchange flow is related to mixing through the salinity variance budget (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1375-1384, doi:10.1175/JPO-D-17-0266.1.
    Description: The relationship between net mixing and the estuarine exchange flow may be quantified using a salinity variance budget. Here “mixing” is defined as the rate of destruction of volume-integrated salinity variance, and the exchange flow is quantified using the total exchange flow. These concepts are explored using an idealized 3D model estuary. It is shown that in steady state (e.g., averaging over the spring–neap cycle) the volume-integrated mixing is approximately given by Mixing ≅ SinSoutQr, where Sin and Sout are the representative salinities of in- and outflowing layers at the mouth and Qr is the river volume flux. This relationship provides an extension of the familiar Knudsen relation, in which the exchange flow is diagnosed based on knowledge of these same three quantities, quantitatively linking mixing to the exchange flow.
    Description: The work was supported by the National Science Foundation through Grants OCE-1736242 to PM and OCE-1736539 to WRG and by the German Research Foundation through Grants TRR 181 and GRK 2000 to HB.
    Keywords: Coastal flows ; Diapycnal mixing ; Ocean dynamics ; Streamflow ; Diagnostics ; Isopycnal coordinates
    Repository Name: Woods Hole Open Access Server
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  • 159
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    Deep eddies in the Gulf of Mexico observed with floats (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 2703-2719, doi:10.1175/JPO-D-17-0245.1.
    Description: A new set of deep float trajectory data collected in the Gulf of Mexico from 2011 to 2015 at 1500- and 2500-m depths is analyzed to describe mesoscale processes, with particular attention paid to the western Gulf. Wavelet analysis is used to identify coherent eddies in the float trajectories, leading to a census of the basinwide coherent eddy population and statistics of the eddies’ kinematic properties. The eddy census reveals a new formation region for anticyclones off the Campeche Escarpment, located northwest of the Yucatan Peninsula. These eddies appear to form locally, with no apparent direct connection to the upper layer. Once formed, the eddies drift westward along the northern edge of the Sigsbee Abyssal Gyre, located in the southwestern Gulf of Mexico over the abyssal plain. The formation mechanism and upstream sources for the Campeche Escarpment eddies are explored: the observational data suggest that eddy formation may be linked to the collision of a Loop Current eddy with the western boundary of the Gulf. Specifically, the disintegration of a deep dipole traveling under the Loop Current eddy Kraken, caused by the interaction with the northwestern continental slope, may lead to the acceleration of the abyssal gyre and the boundary current in the Bay of Campeche region.
    Description: The authors were supported by the Department of the Interior, Bureau of Ocean Energy Management (BOEM), Contract M10PC00112 to Leidos, Inc., Raleigh, North Carolina.
    Description: 2019-05-07
    Keywords: Abyssal circulation ; Currents ; Eddies ; Mesoscale processes ; Trajectories ; In situ oceanic observations
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  • 160
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    Structure and forcing of observed exchanges across the Greenland–Scotland Ridge (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 9881-9901, doi:10.1175/JCLI-D-17-0889.1.
    Description: The Atlantic meridional overturning circulation and associated poleward heat transport are balanced by northern heat loss to the atmosphere and corresponding water-mass transformation. The circulation of northward-flowing Atlantic Water at the surface and returning overflow water at depth is particularly manifested—and observed—at the Greenland–Scotland Ridge where the water masses are guided through narrow straits. There is, however, a rich variability in the exchange of water masses across the ridge on all time scales. Focusing on seasonal and interannual time scales, and particularly the gateways of the Denmark Strait and between the Faroe Islands and Shetland, we specifically assess to what extent the exchanges of water masses across the Greenland–Scotland Ridge relate to wind forcing. On seasonal time scales, the variance explained of the observed exchanges can largely be related to large-scale wind patterns, and a conceptual model shows how this wind forcing can manifest via a barotropic, cyclonic circulation. On interannual time scales, the wind stress impact is less direct as baroclinic mechanisms gain importance and observations indicate a shift in the overflows from being more barotropically to more baroclinically forced during the observation period. Overall, the observed Greenland–Scotland Ridge exchanges reflect a horizontal (cyclonic) circulation on seasonal time scales, while the interannual variability more represents an overturning circulation.
    Description: This research was supported by the Research Council of Norway project NORTH (Grant 229763). Additional support for M. A. Spall was provided by National Science Foundation Grant OCE- 1558742, for T. Eldevik and S. Østerhus by the European Union’s Horizon 2020 research and innovation program project Blue-Action (Grant 727852), and for S. Østerhus by the European Framework Programs under Grant Agreement 308299 (NACLIM).
    Keywords: Ocean circulation ; Thermocline circulation ; Atmosphere-ocean interaction ; North Atlantic Oscillation ; Statistical techniques ; Time series
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  • 161
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    QBO influence on MJO amplitude over the Maritime Continent: Physical mechanisms and seasonality (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Monthly Weather Review 147(1), (2019): 389-406. doi: 10.1175/MWR-D-18-0158.1.
    Description: The quasi-biennial oscillation (QBO) is stratified by stratospheric zonal wind direction and height into four phase pairs [easterly midstratospheric winds (QBOEM), easterly lower-stratospheric winds, westerly midstratospheric winds (QBOWM), and westerly lower-stratospheric winds] using an empirical orthogonal function analysis of daily stratospheric (100–10 hPa) zonal wind data during 1980–2017. Madden–Julian oscillation (MJO) events in which the MJO convective envelope moved eastward across the Maritime Continent (MC) during 1980–2017 are identified using the Real-time Multivariate MJO (RMM) index and the outgoing longwave radiation (OLR) MJO index (OMI). Comparison of RMM amplitudes by the QBO phase pair over the MC (RMM phases 4 and 5) reveals that boreal winter MJO events have the strongest amplitudes during QBOEM and the weakest amplitudes during QBOWM, which is consistent with QBO-driven differences in upper-tropospheric lower-stratospheric (UTLS) static stability. Additionally, boreal winter RMM events over the MC strengthen during QBOEM and weaken during QBOWM. In the OMI, those amplitude changes generally shift eastward to the eastern MC and western Pacific Ocean, which may result from differences in RMM and OMI index methodologies. During boreal summer, as the northeastward-propagating boreal summer intraseasonal oscillation (BSISO) becomes the dominant mode of intraseasonal variability, these relationships are reversed. Zonal differences in UTLS stability anomalies are consistent with amplitude changes of eastward-propagating MJO events across the MC during boreal winter, and meridional stability differences are consistent with amplitude changes of northeastward-propagating BSISO events during boreal summer. Results remain consistent when stratifying by neutral ENSO phase.
    Description: The authors are grateful for the funding provided by the Office of Naval Research Propagation of Intra-Seasonal Tropical Oscillations (ONR PISTON) Award N0001416WX01752 and the USNA Trident Scholar program. The authors also appreciate the helpful comments of the two external reviewers.
    Description: 2019-07-07
    Keywords: Maritime Continent ; Madden-Julian oscillation ; Quasibiennial oscillation
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  • 162
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    The Capo Vaticano (Calabria) coastal terraces and the 1905 M7 earthquake: the geomorphological signature of regional uplift and coseismic slip in southern Italy (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: The elevation of the Capo Vaticano coastal terraces (Tyrrhenian coast, central Calabria) is the result of a combination of regional uplift and repeated coseismic displacement. We subtract the regional uplift from the total uplift (maximum average uplift rates: 0.81–0.97 mm a)1 since c. 0.7 Ma) and obtain the residual fault-related displacement. Then, we model the residual displacement to provide constraints on the location and geometry of the seismogenic source of the 1905 M7 earthquake, the strongest – and still poorly understood – earthquake of the instrumental era in this area. We try four different potential sources for the dislocation modelling and find that (1) three sources are not compatible with the displacement observed along the terraces and (2) the only source consistent with the local deformation is the 100 - striking Coccorino Fault. We calculate average long-term vertical slip rates of 0.2–0.3 mm a)1 on the Coccorino Fault and estimate an average recurrence time of one millennium for a 1905-type earthquake.
    Description: Published
    Description: 378-389
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: 1905 earthquake ; marine terraces ; coseismic displacement ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Accounting for source effects in the ShakeMap procedure: the 2000 Tottori and the 2008 Miyagi earthquakes (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: Real-time seismology has made significant improvements in recent years, with source parameters now available within a few tens of minutes after an earthquake. It is likely that this time will be further reduced, in the near future, by means of increased efficiency in real-time transmission,increasingdatacoverageandimprovementofthemethodologies.Inthiscontext, together with the development of new ground motion predictive equations (GMPEs) that are abletoaccountforsourcecomplexity,thegenerationofstronggroundmotionshakingmapsin quasi-real time has become ever more feasible after the occurrence of a damaging earthquake. However, GMPEs may not reproduce reliably the ground motion in the near-source region where the finite fault parameters have a strong influence on the shaking. Inthispaperwetestwhetheraccountingforsource-relatedeffectsiseffectiveinbettercharacterizingthegroundmotion.WeintroduceamodificationoftheGMPEswithintheShakeMap softwarepackage,andsubsequentlytesttheaccuracyofthenewlygeneratedshakemapsinpredictingthegroundmotion.ThetestisconductedbycontrollingtheperformanceofShakeMap as we decrease the amount of the available information. We then update ShakeMap with the GMPE modified with a corrective factor accounting for source effects, in order to better constrain these effects that likely influence the level of (near-source) ground shaking. Weinvestigatetwowell-recordedearthquakesfromJapan(the2000Tottori, Mw 6.6,andthe 2008 Iwate-Miyagi, Mw7.0, events) where the instrumental coverage is as dense as needed to ensure an objective appraisal of the results. The results demonstrate that the corrected GMPE can capture only some aspects of the ground shaking in the near-source area, neglecting other multidimensional effects, such as propagation effects and local site amplification.
    Description: Italian Presidenza del Consiglio dei Ministri, Dipartimento della Protezione Civile(DPC)under the contract 2007–2009 DPC-INGVS3project
    Description: Published
    Description: 1836-1848
    Description: 3T. Pericolosità sismica e contributo alla definizione del rischio
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake ground motions ; Earthquake source observation ; Computational seismology ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.04. Ground motion ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.06. Seismology::04.06.11. Seismic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 164
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    How fast was the Matuyama-Brunhes geomagnetic reversal? A new subcentennial record from the Sulmona Basin, central Italy (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2017-04-04
    Description: A recent study of the Matuyama–Brunhes (M-B) geomagnetic field reversal recorded in exposed lacustrine sediments from the Sulmona Basin (Italy) provided a continuous, highresolution record indicating that the reversal of the field direction at the terminus of the M-B boundary (MBB) occurred in less than a century, about 786 ka ago. In the sediment, thin (4–6 cm) remagnetized horizons were recognized above two distinct tephra layers—SUL2- 19 and SUL2-20—that occur ∼25 and ∼35 cm below the MBB, respectively. Also, a faint, millimetre-thick tephra (SUL2-18) occurs 2–3 cm above the MBB.With the aim of improving the temporal resolution of the previous Sulmona MBB record and understanding the possible influence of cryptotephra on the M-B record in the Sulmona Basin,we performed more detailed sampling and analyses of overlapping standard and smaller samples from a 50 cm-long block that spans the MBB. The new data indicate that (i) the MBB is even sharper than previously reported and occurs ∼2.5 cm below tephra SUL2-18, in agreement with the previous study; (ii) the MBB coincides with the rise of an intensity peak of the natural remanent magnetization (NRM) intensity, which extends across SUL2-18; (iii) except for a 2-cm-thick interval just above tephra SUL2-18, the rock magnetic parameters (k, ARM, Mr, Ms, Bc, Bcr) indicate exactly the same magnetic mineralogy throughout the sampled sequence. We conclude that either SUL2-18 resulted in the remagnetization of an interval of about 6 cm (i.e. during the NRM intensity peak spanning ∼260 ± 110 yr, according to the estimated local sedimentation rate), and thus the detailed MBB record is lost because it is overprinted, or the MBB is well recorded, occurred abruptly about 2.5 cm below SUL2-18 and lasted less than 13 ± 6 yr. Both hypotheses challenge our understanding of the geomagnetic field behaviour during a polarity transition and/or of the NRM acquisition process in the Sulmona lacustrine sediment.
    Description: Published
    Description: 798-812
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Palaeomagnetic secular variation; Rapid time variations; Reversals: process, time scale, magnetostratigraphy; Rock and mineral magnetism ; 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 165
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    A Unique Capsular Polysaccharide Structure from the Psychrophilic Marine Bacterium Colwellia psychrerythraea 34H That Mimics Antifreeze (Glyco)proteins (2015)
    American Chemical Society
    In:  EPIC3Journal of the American Chemical Society, American Chemical Society, 137(1), pp. 179-189, ISSN: 0002-7863
    Details
    Publication Date: 2019-07-17
    Description: The low temperatures of polar regions and high-altitude environments, especially icy habitats, present challenges for many microorganisms. Their ability to live under subfreezing conditions implies the production of compounds conferring cryotolerance. Colwellia psychrerythraea 34H, a γ-proteobacterium isolated from subzero Arctic marine sediments, provides a model for the study of life in cold environments. We report here the identification and detailed molecular primary and secondary structures of capsular polysaccharide from C. psychrerythraea 34H cells. The polymer was isolated in the water layer when cells were extracted by phenol/water and characterized by one- and two-dimensional NMR spectroscopy together with chemical analysis. Molecular mechanics and dynamics calculations were also performed. The polysaccharide consists of a tetrasaccharidic repeating unit containing two amino sugars and two uronic acids bearing threonine as substituent. The structural features of this unique polysaccharide resemble those present in antifreeze proteins and glycoproteins. These results suggest a possible correlation between the capsule structure and the ability of C. psychrerythraea to colonize subfreezing marine environments.
    Repository Name: EPIC Alfred Wegener Institut
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    On serial observation processing in localized ensemble Kalman filters (2015)
    American Meteorological Society
    In:  EPIC3Monthly Weather Review, American Meteorological Society, 143, pp. 1554-1567, ISSN: 0027-0644
    Details
    Publication Date: 2019-07-17
    Description: Ensemble square root filters can either assimilate all observations that are available at a given time at once, or assimilate the observations in batches or one at a time. For large-scale models, the filters are typically applied with a localized analysis step. This study demonstrates that the interaction of serial observation processing and localization can destabilize the analysis process and examines under which conditions the instability becomes significant. The instability results from a repeated inconsistent update of the state error covariance matrix that is caused by the localization. The inconsistency is present in all ensemble Kalman filters, except the classical ensemble Kalman filter with perturbed observations. With serial observation processing, its effect is small in cases when the assimilation changes the ensemble of model states only slightly. However, when the assimilation has a strong effect on the state estimates, the interaction of localization and serial observation processing can significantly deteriorate the filter performance. In realistic large-scale applications, when the assimilation changes the states only slightly and when the distribution of the observations is irregular and changing over time, the instability is likely not significant.
    Repository Name: EPIC Alfred Wegener Institut
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  • 167
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    Ozonesonde Quality Assurance: The JOSIE–SHADOZ (2017) Experience (2019)
    American Meteorological Society
    In:  EPIC3Bulletin of the American Meteorological Society, American Meteorological Society, 100(1), pp. 155-171, ISSN: 0003-0007
    Details
    Publication Date: 2019-10-29
    Description: The ozonesonde is a small balloon-borne instrument that is attached to a standard radiosonde to measure profiles of ozone from the surface to 35 km with ∼100-m vertical resolution. Ozonesonde data constitute a mainstay of satellite calibration and are used for climatologies and analysis of trends, especially in the lower stratosphere where satellites are most uncertain. The electrochemical concentration cell (ECC) ozonesonde has been deployed at ∼100 stations worldwide since the 1960s, with changes over time in manufacture and procedures, including details of the cell chemical solution and data processing. As a consequence, there are biases among different stations and discontinuities in profile time series from individual site records. For 22 years the Jülich (Germany) Ozonesonde Intercomparison Experiment (JOSIE) has periodically tested ozonesondes in a simulation chamber designated the World Calibration Centre for Ozonesondes (WCCOS) by WMO. During October–November 2017 a JOSIE campaign evaluated the sondes and procedures used in Southern Hemisphere Additional Ozonesondes (SHADOZ), a 14-station sonde network operating in the tropics and subtropics. A distinctive feature of the 2017 JOSIE was that the tests were conducted by operators from eight SHADOZ stations. Experimental protocols for the SHADOZ sonde configurations, which represent most of those in use today, are described, along with preliminary results. SHADOZ stations that follow WMO-recommended protocols record total ozone within 3% of the JOSIE reference instrument. These results and prior JOSIEs demonstrate that regular testing is essential to maintain best practices in ozonesonde operations and to ensure high-quality data for the satellite and ozone assessment communities.
    Repository Name: EPIC Alfred Wegener Institut
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  • 168
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    Source modelling of the M5-6 Emilia-Romagna, Italy, earthquakes (May 20-29, 2012) (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2021-11-25
    Description: On 2012 May 20 and 29, two damaging earthquakes with magnitudes Mw 6.1 and 5.9, respectively, struck the Emilia-Romagna region in the sedimentary Po Plain, Northern Italy, causing 26 fatalities, significant damage to historical buildings and substantial impact to the economy of the region. The earthquake sequence included four more aftershocks with Mw ? 5.0, all at shallow depths (about 7–9 km), with similar WNW–ESE striking reverse mechanism. The timeline of the sequence suggests significant static stress interaction between the largest events. We perform here a detailed source inversion, first adopting a point source approximation and considering pure double couple and full moment tensor source models. We compare different extended source inversion approaches for the two largest events, and find that the rupture occurred in both cases along a subhorizontal plane, dipping towards SSW. Directivity is well detected for the May 20 main shock, indicating that the rupture propagated unilaterally towards SE. Based on the focal mechanism solution, we further estimate the co-seismic static stress change induced by the May 20 event. By using the rate-and-state model and a Poissonian earthquake occurrence, we infer that the second largest event of May 29 was induced with a probability in the range 0.2–0.4. This suggests that the segment of fault was already prone to rupture. Finally, we estimate peak ground accelerations for the two main events as occurred separately or simultaneously. For the scenario involving hypothetical rupture areas of both main events, we estimate Mw = 6.3 and an increase of ground acceleration by 50 per cent. The approach we propose may help to quantify rapidly which regions are invested by a significant increase of the hazard, bearing the potential for large aftershocks or even a second main shock.
    Description: Published
    Description: 1658-1672
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: Earthquake dynamics ; Earthquake source observations ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Prediction of Indian summer monsoon onset using dynamical sub-seasonal forecasts: effects of realistic initialization of the atmosphere (2015)
    American Meteorological Society
    Details
    Publication Date: 2021-11-09
    Description: Ensembles of retrospective 2-month dynamical forecasts initiated on 1May are used to predict the onset of the Indian summer monsoon (ISM) for the period 1989–2005. The subseasonal predictions (SSPs) are based on a coupled general circulation model and recently they have been upgraded by the realistic initialization of the atmosphere with initial conditions taken from reanalysis. Two objective large-scale methods based on dynamical circulation and hydrological indices are applied to detect the ISM onset. The SSPs show some skill in forecasting earlier-than-normal ISM onsets, while they have difficulty in predicting late onsets. It is shown that significant contribution to the skill in forecasting early ISM onsets comes from the newly developed initialization of the atmosphere from reanalysis. On one hand, atmospheric initialization produces a better representation of the atmospheric mean state in the initial conditions, leading to a systematically improved monsoon onset sequence. On the other hand, the initialization of the atmosphere allows some skill in forecasting the northward propagating intraseasonal wind and precipitation anomalies over the tropical Indian Ocean. The northward propagating intraseasonal modes trigger the monsoon in some early-onset years. The realistic phase initialization of these modes improves the forecasts of the associated earlier-than-normal monsoon onsets. The prediction of late onsets is not noticeably improved by the initialization of the atmosphere. It is suggested that late onsets of the monsoon are too far away from the start date of the forecasts to conserve enough memory of the intraseasonal oscillation (ISO) anomalies and of the improved representation of the mean state in the initial conditions.
    Description: Published
    Description: 778-793
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: indian summer monsoon ; onset ; seasonal predictions ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate ; 01. Atmosphere::01.01. Atmosphere::01.01.04. Processes and Dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    A hybrid particle–ensemble Kalman filter for Lagrangian data assimilation (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Monthly Weather Review 143 (2015): 195–211, doi:10.1175/MWR-D-14-00051.1.
    Description: Lagrangian measurements from passive ocean instruments provide a useful source of data for estimating and forecasting the ocean’s state (velocity field, salinity field, etc.). However, trajectories from these instruments are often highly nonlinear, leading to difficulties with widely used data assimilation algorithms such as the ensemble Kalman filter (EnKF). Additionally, the velocity field is often modeled as a high-dimensional variable, which precludes the use of more accurate methods such as the particle filter (PF). Here, a hybrid particle–ensemble Kalman filter is developed that applies the EnKF update to the potentially high-dimensional velocity variables, and the PF update to the relatively low-dimensional, highly nonlinear drifter position variable. This algorithm is tested with twin experiments on the linear shallow water equations. In experiments with infrequent observations, the hybrid filter consistently outperformed the EnKF, both by better capturing the Bayesian posterior and by better tracking the truth.
    Description: The work of Apte benefited from the support of the AIRBUS Group Corporate Foundation Chair in Mathematics of Complex Systems established in ICTS-TIFR. Spiller would like to acknowledge support by NSF Grant DMS-1228265 and ONR Grant N00014-11-1-0087. Sandstede gratefully acknowledges support by the NSF through Grant DMS-0907904. Slivinski was supported by the NSF through Grants DMS-0907904 and DMS-1148284.
    Description: 2015-07-01
    Keywords: Bayesian methods ; Filtering techniques ; Kalman filters ; Statistical techniques ; Data assimilation
    Repository Name: Woods Hole Open Access Server
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    Corrigendum (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 31 (2014): 2871, doi:10.1175/JTECH-D-14-00187.1.
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  • 172
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    Continental shelf baroclinic instability. Part I : relaxation from upwelling or downwelling (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 551-568, doi:10.1175/JPO-D-15-0047.1.
    Description: There exists a good deal of indirect evidence, from several locations around the world, that there is a substantial eddy field over continental shelves. These eddies appear to have typical swirl velocities of a few centimeters per second and have horizontal scales of perhaps 5–10 km. These eddies are weak compared to typical, wind-driven, alongshore flows but often seem to dominate middepth cross-shelf flows. The idea that motivates the present contribution is that the alongshore wind stress ultimately energizes these eddies by means of baroclinic instabilities, even in cases where obvious intense fronts do not exist. The proposed sequence is that alongshore winds over a stratified ocean cause upwelling or downwelling, and the resulting horizontal density gradients are strong enough to fuel baroclinic instabilities of the requisite energy levels. This idea is explored here by means of a sequence of idealized primitive equation numerical model studies, each driven by a modest, nearly steady, alongshore wind stress applied for about 5–10 days. Different runs vary wind forcing, stratification, bottom slope, bottom friction, and Coriolis parameter. All runs, both upwelling and downwelling, are found to be baroclinically unstable and to have scales compatible with the underlying hypothesis. The model results, combined with physically based scalings, show that eddy kinetic energy generally increases with bottom slope, stratification, wind impulse (time integral of the wind stress), and inverse Coriolis parameter. The dominant length scale of the eddies is found to increase with increasing eddy kinetic energy and to decrease with Coriolis parameter.
    Description: This work was supported by the Woods Hole Oceanographic Institution and by the National Science Foundation, Physical Oceanography section through Grant OCE-1433953.
    Description: 2016-06-09
    Keywords: Geographic location/entity ; Continental shelf/slope ; Variability ; Oceanic variability
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  • 173
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    Enhanced diapycnal diffusivity in intrusive regions of the Drake Passage (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1309-1321, doi:10.1175/JPO-D-15-0068.1.
    Description: Direct measurements of oceanic turbulent parameters were taken upstream of and across Drake Passage, in the region of the Subantarctic and Polar Fronts. Values of turbulent kinetic energy dissipation rate ε estimated by microstructure are up to two orders of magnitude lower than previously published estimates in the upper 1000 m. Turbulence levels in Drake Passage are systematically higher than values upstream, regardless of season. The dissipation of thermal variance χ is enhanced at middepth throughout the surveys, with the highest values found in northern Drake Passage, where water mass variability is the most pronounced. Using the density ratio, evidence for double-diffusive instability is presented. Subject to double-diffusive physics, the estimates of diffusivity using the Osborn–Cox method are larger than ensemble statistics based on ε and the buoyancy frequency.
    Description: This work was supported by grants from the U.S. National Science Foundation.
    Description: 2016-10-05
    Keywords: Geographic location/entity ; Southern Ocean ; Circulation/ Dynamics ; Diapycnal mixing ; Mixing ; Turbulence ; Atm/Ocean Structure/ Phenomena ; Fronts ; Observational techniques and algorithms ; Profilers, oceanic
    Repository Name: Woods Hole Open Access Server
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    Eddy–wind interaction in the California Current System : dynamics and impacts (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 439-459, doi:10.1175/JPO-D-15-0086.1.
    Description: The summertime California Current System (CCS) is characterized by energetic mesoscale eddies, whose sea surface temperature (SST) and surface current can significantly modify the wind stress and Ekman pumping. Relative importance of the eddy–wind interactions via SST and surface current in the CCS is examined using a high-resolution (7 km) regional coupled model with a novel coupling approach to isolate the small-scale air–sea coupling by SST and surface current. Results show that when the eddy-induced surface current is allowed to modify the wind stress, the spatially averaged surface eddy kinetic energy (EKE) is reduced by 42%, and this is primarily due to enhanced surface eddy drag and reduced wind energy transfer. In contrast, the eddy-induced SST–wind coupling has no significant impact on the EKE. Furthermore, eddy-induced SST and surface current modify the Ekman pumping via their crosswind SST gradient and surface vorticity gradient, respectively. The resultant magnitudes of the Ekman pumping velocity are comparable, but the implied feedback effects on the eddy statistics are different. The surface current-induced Ekman pumping mainly attenuates the amplitude of cyclonic and anticyclonic eddies, acting to reduce the eddy activity, while the SST-induced Ekman pumping primarily affects the propagation. Time mean–rectified change in SST is determined by the altered offshore temperature advection by the mean and eddy currents, but the magnitude of the mean SST change is greater with the eddy-induced current effect. The demonstrated remarkably strong dynamical response in the CCS system to the eddy-induced current–wind coupling indicates that eddy-induced current should play an important role in the regional coupled ocean–atmosphere system.
    Description: We thank NSF for support under GrantsOCE-0960770,OCE-1419235, andOCE-1419306. HS is grateful for the WHOI internal support from the Andrew W. Mellon Foundation Awards for Innovative Research and the additional support from the ONR We thank NSF for support under GrantsOCE-0960770,OCE-1419235, andOCE-1419306. HS is grateful for the WHOI internal support from the Andrew W. Mellon Foundation Awards for Innovative Research and the additional support from the ONR
    Description: 2016-05-30
    Keywords: Atm/Ocean Structure/ Phenomena ; Atmosphere-ocean interaction ; Ekman pumping ; Models and modeling ; Ocean models ; Regional models
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    Stratified turbulence and mixing efficiency in a salt wedge estuary (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1769-1783, doi:10.1175/JPO-D-15-0193.1.
    Description: High-resolution observations of velocity, salinity, and turbulence quantities were collected in a salt wedge estuary to quantify the efficiency of stratified mixing in a high-energy environment. During the ebb tide, a midwater column layer of strong shear and stratification developed, exhibiting near-critical gradient Richardson numbers and turbulent kinetic energy (TKE) dissipation rates greater than 10−4 m2 s−3, based on inertial subrange spectra. Collocated estimates of scalar variance dissipation from microconductivity sensors were used to estimate buoyancy flux and the flux Richardson number Rif. The majority of the samples were outside the boundary layer, based on the ratio of Ozmidov and boundary length scales, and had a mean Rif = 0.23 ± 0.01 (dissipation flux coefficient Γ = 0.30 ± 0.02) and a median gradient Richardson number Rig = 0.25. The boundary-influenced subset of the data had decreased efficiency, with Rif = 0.17 ± 0.02 (Γ = 0.20 ± 0.03) and median Rig = 0.16. The relationship between Rif and Rig was consistent with a turbulent Prandtl number of 1. Acoustic backscatter imagery revealed coherent braids in the mixing layer during the early ebb and a transition to more homogeneous turbulence in the midebb. A temporal trend in efficiency was also visible, with higher efficiency in the early ebb and lower efficiency in the late ebb when the bottom boundary layer had greater influence on the flow. These findings show that mixing efficiency of turbulence in a continuously forced, energetic, free shear layer can be significantly greater than the broadly cited upper bound from Osborn of 0.15–0.17.
    Description: Holleman was supported by the Devonshire Scholars program. The field study and the coauthors’ contributions were supported by NSF Grant OCE 0926427.
    Description: 2016-11-24
    Keywords: Circulation/ Dynamics ; Mixing ; Shear structure/flows ; Turbulence ; Observational techniques and algorithms ; Ship observations
    Repository Name: Woods Hole Open Access Server
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    Comparison of direct covariance flux measurements from an offshore tower and a buoy (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: © The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Atmospheric and Oceanic Technology 33 (2016): 873-890, doi:10.1175/JTECH-D-15-0109.1.
    Description: Direct covariance flux (DCF) measurements taken from floating platforms are contaminated by wave-induced platform motions that need to be removed before computation of the turbulent fluxes. Several correction algorithms have been developed and successfully applied in earlier studies from research vessels and, most recently, by the use of moored buoys. The validation of those correction algorithms has so far been limited to short-duration comparisons against other floating platforms. Although these comparisons show in general a good agreement, there is still a lack of a rigorous validation of the method, required to understand the strengths and weaknesses of the existing motion-correction algorithms. This paper attempts to provide such a validation by a comparison of flux estimates from two DCF systems, one mounted on a moored buoy and one on the Air–Sea Interaction Tower (ASIT) at the Martha’s Vineyard Coastal Observatory, Massachusetts. The ASIT was specifically designed to minimize flow distortion over a wide range of wind directions from the open ocean for flux measurements. The flow measurements from the buoy system are corrected for wave-induced platform motions before computation of the turbulent heat and momentum fluxes. Flux estimates and cospectra of the corrected buoy data are found to be in very good agreement with those obtained from the ASIT. The comparison is also used to optimize the filter constants used in the motion-correction algorithm. The quantitative agreement between the buoy data and the ASIT demonstrates that the DCF method is applicable for turbulence measurements from small moving platforms, such as buoys.
    Description: This work was funded by the National Science Foundation Grant OCE04-24536 as part of the CLIVAR Mode Water Dynamic Experiment (CLIMODE).
    Keywords: Circulation/ Dynamics ; Turbulence ; Atm/Ocean Structure/ Phenomena ; Boundary layer ; Physical Meteorology and Climatology ; Air-sea interaction ; Observational techniques and algorithms ; Buoy observations ; Quality assurance/control
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    LOBSTAHS : an adduct-based lipidomics strategy for discovery and identification of oxidative stress biomarkers (2016)
    American Chemical Society
    Details
    Publication Date: 2022-05-26
    Description: © The American Chemical Society, 2016. This is an open access article published under an ACS AuthorChoice License. The definitive version was published in Analytical Chemistry 88 (2016): 7154–7162, doi:10.1021/acs.analchem.6b01260.
    Description: Discovery and identification of molecular biomarkers in large LC/MS data sets requires significant automation without loss of accuracy in the compound screening and annotation process. Here, we describe a lipidomics workflow and open-source software package for high-throughput annotation and putative identification of lipid, oxidized lipid, and oxylipin biomarkers in high-mass-accuracy HPLC-MS data. Lipid and oxylipin biomarker screening through adduct hierarchy sequences, or LOBSTAHS, uses orthogonal screening criteria based on adduct ion formation patterns and other properties to identify thousands of compounds while providing the user with a confidence score for each assignment. Assignments are made from one of two customizable databases; the default databases contain 14 068 unique entries. To demonstrate the software’s functionality, we screened more than 340 000 mass spectral features from an experiment in which hydrogen peroxide was used to induce oxidative stress in the marine diatom Phaeodactylum tricornutum. LOBSTAHS putatively identified 1969 unique parent compounds in 21 869 features that survived the multistage screening process. While P. tricornutum maintained more than 92% of its core lipidome under oxidative stress, patterns in biomarker distribution and abundance indicated remodeling was both subtle and pervasive. Treatment with 150 μM H2O2 promoted statistically significant carbon-chain elongation across lipid classes, with the strongest elongation accompanying oxidation in moieties of monogalactosyldiacylglycerol, a lipid typically localized to the chloroplast. Oxidative stress also induced a pronounced reallocation of lipidome peak area to triacylglycerols. LOBSTAHS can be used with environmental or experimental data from a variety of systems and is freely available at https://github.com/vanmooylipidomics/LOBSTAHS.
    Description: This research was supported by the Gordon and Betty Moore Foundation through Grant GBMF3301 to B.A.S.V.M. This research was also funded in part by a grant to B.A.S.V.M. from the Simons Foundation and is a contribution of the Simons Collaboration on Ocean Processes and Ecology (SCOPE). J.R.C. acknowledges support from a U.S. Environmental Protection Agency (EPA) STAR Graduate Fellowship (Fellowship Assistance Agreement No. FP-91744301-0).
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    Recent tropical expansion: natural variability or forced response? (2019)
    American Meteorological Society
    Details
    Publication Date: 2023-02-23
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 32(5) (2019): 1551-1571. doi:10.1175/JCLI-D-18-0444.1.
    Description: Previous studies have documented a poleward shift in the subsiding branches of Earth’s Hadley circulation since 1979 but have disagreed on the causes of these observed changes and the ability of global climate models to capture them. This synthesis paper reexamines a number of contradictory claims in the past literature and finds that the tropical expansion indicated by modern reanalyses is within the bounds of models’ historical simulations for the period 1979–2005. Earlier conclusions that models were underestimating the observed trends relied on defining the Hadley circulation using the mass streamfunction from older reanalyses. The recent observed tropical expansion has similar magnitudes in the annual mean in the Northern Hemisphere (NH) and Southern Hemisphere (SH), but models suggest that the factors driving the expansion differ between the hemispheres. In the SH, increasing greenhouse gases (GHGs) and stratospheric ozone depletion contributed to tropical expansion over the late twentieth century, and if GHGs continue increasing, the SH tropical edge is projected to shift further poleward over the twenty-first century, even as stratospheric ozone concentrations recover. In the NH, the contribution of GHGs to tropical expansion is much smaller and will remain difficult to detect in a background of large natural variability, even by the end of the twenty-first century. To explain similar recent tropical expansion rates in the two hemispheres, natural variability must be taken into account. Recent coupled atmosphere–ocean variability, including the Pacific decadal oscillation, has contributed to tropical expansion. However, in models forced with observed sea surface temperatures, tropical expansion rates still vary widely because of internal atmospheric variability.
    Description: We thank Ori Adam, Nick Davis, Isaac Held, Tim Merlis, Lorenzo Polvani, and one anonymous reviewer for helpful comments and suggestions. We thank U.S. CLIVAR and the International Space Science Institute (ISSI) for funding working groups that stimulated this project. We thank all members of the working groups for helpful discussions, and the U.S. CLIVAR and ISSI offices and their sponsoring agencies (NASA,NOAA,NSF,DOE, ESA, Swiss Confederation, Swiss Academy of Sciences, and University of Bern) for supporting these groups and activities.We acknowledge WCRP’sWorking Group on CoupledModelling, which is responsible for CMIP, and we thank the climate modeling groups (Table 2) for producing and making available their model output. For CMIP, the U.S. DOE PCMDI provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portals.
    Description: 2019-08-06
    Keywords: Hadley circulation ; Climate models ; Reanalysis data ; Multidecadal variability ; Pacific decadal oscillation ; Trends
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    Spatial variability of volcanic features in early-stage rift settings: the case of the Tanzania Divergence, East African rift system (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: Close relationships between deformation and volcanism are well documented in relatively late evolutionary stages of con- tinental rifting, whereas these are poorly constrained in less mature rifting stages. To investigate the control of inherited structures on faulting and volcanism, we present a statistical analysis of volcanic features, faults and pre-rift fabric in the Tanzania Divergence, where volcanic features occur exten- sively in in-rift and off-rift areas. Our results show that in mature rift sectors (Natron), magma uprising is mostly con- trolled by fractures/faults responding to the far-field stress, whereas the distribution of volcanism during initial rifting (Eyasi) is controlled by inherited structures oblique to the regional extension direction. Off-rift sectors show a marked control of pre-rift structures on magma emplacement, which may not respond to the regional stress field. Thus, the use of off-rift magmatic features as stress indicators should take into account the role of pre-existing structures.
    Description: Published
    Description: 461-468
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: East Africa Rift System, Tanzania-Kenia, structures and volcanism ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Frontogenesis and variability in Denmark Strait and its influence on overflow water (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(7), (2019): 1889-1904, doi:10.1175/JPO-D-19-0053.1.
    Description: A high-resolution numerical model, together with in situ and satellite observations, is used to explore the nature and dynamics of the dominant high-frequency (from one day to one week) variability in Denmark Strait. Mooring measurements in the center of the strait reveal that warm water “flooding events” occur, whereby the North Icelandic Irminger Current (NIIC) propagates offshore and advects subtropical-origin water northward through the deepest part of the sill. Two other types of mesoscale processes in Denmark Strait have been described previously in the literature, known as “boluses” and “pulses,” associated with a raising and lowering of the overflow water interface. Our measurements reveal that flooding events occur in conjunction with especially pronounced pulses. The model indicates that the NIIC hydrographic front is maintained by a balance between frontogenesis by the large-scale flow and frontolysis by baroclinic instability. Specifically, the temperature and salinity tendency equations demonstrate that the eddies act to relax the front, while the mean flow acts to sharpen it. Furthermore, the model reveals that the two dense water processes—boluses and pulses (and hence flooding events)—are dynamically related to each other and tied to the meandering of the hydrographic front in the strait. Our study thus provides a general framework for interpreting the short-time-scale variability of Denmark Strait Overflow Water entering the Irminger Sea.
    Description: MAS was supported by the National Science Foundation (NSF) under Grants OCE-1558742 and OCE-1534618. RSP, PL, and DM were supported by NSF under Grants OCE-1558742 and OCE-1259618. WJvA was supported by the Helmholtz Infrastructure Initiative FRAM. TWNH and MA were supported by NSF under Grants OCE-1633124 and OCE-118123.
    Description: 2020-07-01
    Keywords: Baroclinic flows ; Frontogenesis/frontolysis ; Meridional overturning circulation ; Ocean dynamics ; Topographic effects
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    Sediment transport model including short-lived radioisotopes: Model description and idealized test cases (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-10-27
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Marine Science and Engineering 6(4), (2018): 144. doi:10.3390/jmse6040144.
    Description: Geochronologies derived from sediment cores in coastal locations are often used to infer event bed characteristics such as deposit thicknesses and accumulation rates. Such studies commonly use naturally occurring, short-lived radioisotopes, such as Beryllium-7 (7Be) and Thorium-234 (234Th), to study depositional and post-depositional processes. These radioisotope activities, however, are not generally represented in sediment transport models that characterize coastal flood and storm deposition with grain size patterns and deposit thicknesses. We modified the Community Sediment Transport Modeling System (CSTMS) to account for reactive tracers and used this capability to represent the behavior of these short-lived radioisotopes on the sediment bed. This paper describes the model and presents results from a set of idealized, one-dimensional (vertical) test cases. The model configuration represented fluvial deposition followed by periods of episodic storm resuspension. Sensitivity tests explored the influence on seabed radioisotope profiles by the intensities of bioturbation and wave resuspension and the thickness of fluvial deposits. The intensity of biodiffusion affected the persistence of fluvial event beds as evidenced by 7Be. Both resuspension and biodiffusion increased the modeled seabed inventory of 234Th. A thick fluvial deposit increased the seabed inventory of 7Be and 234Th but mixing over time greatly reduced the difference in inventory of 234Th in fluvial deposits of different thicknesses.
    Description: The Bureau of Ocean Energy Management (BOEM) provided funding for Birchler, Harris, and Kniskern. During his M.S. program Birchler received additional funds from VIMS’ Office of Academic Studies. This work was partially supported by the U.S. Geological Survey, Coastal and Marine Geology Program.
    Keywords: Numerical model ; Sediment transport ; Marine ; Short-lived radioisotopes
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    Moored observations of the surface meteorology and air-sea fluxes in the Northern Bay of Bengal in 2015 (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 32(2), (2019): 549-573. doi: 10.1175/JCLI-D-18-0413.1.
    Description: Time series of surface meteorology and air–sea fluxes from the northern Bay of Bengal are analyzed, quantifying annual and seasonal means, variability, and the potential for surface fluxes to contribute significantly to variability in surface temperature and salinity. Strong signals were associated with solar insolation and its modulation by cloud cover, and, in the 5- to 50-day range, with intraseasonal oscillations (ISOs). The northeast (NE) monsoon (DJF) was typically cloud free, with strong latent heat loss and several moderate wind events, and had the only seasonal mean ocean heat loss. The spring intermonsoon (MAM) was cloud free and had light winds and the strongest ocean heating. Strong ISOs and Tropical Cyclone Komen were seen in the southwest (SW) monsoon (JJA), when 65% of the 2.2-m total rain fell, and oceanic mean heating was small. The fall intermonsoon (SON) initially had moderate convective systems and mean ocean heating, with a transition to drier winds and mean ocean heat loss in the last month. Observed surface freshwater flux applied to a layer of the observed thickness produced drops in salinity with timing and magnitude similar to the initial drops in salinity in the summer monsoon, but did not reproduce the salinity variability of the fall intermonsoon. Observed surface heat flux has the potential to cause the temperature trends of the different seasons, but uncertainty in how shortwave radiation is absorbed in the upper ocean limits quantifying the role of surface forcing in the evolution of mixed layer temperature.
    Description: The deployment of the Woods Hole Oceanographic Institution (WHOI) mooring and RW and JTF were supported by the U.S. Office of Naval Research, Grant N00014-13-1-0453. DS acknowledges support from the Ministry of Earth Sciences under India’s National Monsoon Mission. HS acknowledges support from the Office of Naval Research Grants N00014-13-1-0453 and N00014-17-12398. The deployment of the WHOI mooring was done by RV Sagar Nidhi and the recovery by RV Sagar Kanya; the help of the crew and science parties is gratefully acknowledged as is the ongoing support at NIOT in Chennai and by other colleagues in India of this mooring work. The work of the staff of the WHOI Upper Ocean Process Group in the design, building, deployment, and recovery of the mooring and in processing the data is gratefully acknowledged. The software for the wavelet analysis was provided by Torrence and Compo (1998). Feedback on the paper by Dr. Amit Tandon and two anonymous reviewers is gratefully acknowledged. This paper is dedicated to Dr. Frank Bradley.
    Description: 2019-06-28
    Keywords: Atmosphere-ocean interaction ; Monsoons ; Air-sea interaction ; Surface fluxes
    Repository Name: Woods Hole Open Access Server
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  • 183
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    Ocean Dumping of Containerized DDT Waste Was a Sloppy Process (2019)
    American Chemical Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Chemical Society, 2019. This article is posted here by permission of American Chemical Society for personal use, not for redistribution. The definitive version was published in Kivenson, V., Lemkau, K. L., Pizarro, O., Yoerger, D. R., Kaiser, C., Nelson, R. K., Carmichael, C., Paul, B. G., Reddy, C. M., & Valentine, D. L. (2019). Ocean Dumping of Containerized DDT Waste Was a Sloppy Process. Environmental Science and Technology (2019), doi:10.1021/acs.est.8b05859.
    Description: Industrial-scale dumping of organic waste to the deep ocean was once common practice, leaving a legacy of chemical pollution for which a paucity of information exists. Using a nested approach with autonomous and remotely operated underwater vehicles, a dumpsite offshore California was surveyed and sampled. Discarded waste containers littered the site and structured the suboxic benthic environment. Dichlorodiphenyltrichloroethane (DDT) was reportedly dumped in the area, and sediment analysis revealed substantial variability in concentrations of p,p-DDT and its analogs, with a peak concentration of 257 μg g–1, ∼40 times greater than the highest level of surface sediment contamination at the nearby DDT Superfund site. The occurrence of a conspicuous hydrocarbon mixture suggests that multiple petroleum distillates, potentially used in DDT manufacture, contributed to the waste stream. Application of a two end-member mixing model with DDTs and polychlorinated biphenyls enabled source differentiation between shelf discharge versus containerized waste. Ocean dumping was found to be the major source of DDT to more than 3000 km2 of the region’s deep seafloor. These results reveal that ocean dumping of containerized DDT waste was inherently sloppy, with the contents readily breaching containment and leading to regional scale contamination of the deep benthos.
    Description: This material is based upon work supported by the National Science Foundation Graduate Research Fellowship for V.K. under Grant No. 1650114. Expeditions AT-18-11 and AT-26-06 were funded by the NSF (OCE-0961725 and OCE-1046144). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. We thank the captain and crew of the RV Atlantis, the pilots and crew of the ROV Jason, the crew of the AUV Sentry, the scientific party of the AT-18-11 and AT-26-06 expeditions, Justin Tran for assistance with the preparation of multibeam data, M. Indira Venkatesan for a helpful discussion of the NOAA datasets, and Nathan Dodder for advice on the procedure for compound identification.
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  • 184
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    On material transport by shelfbreak eddies (2019)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography, 49 (2), (2019): 607-630, doi:10.1175/JPO-D-18-0166.1.
    Description: The Lagrangian motion in the eddy field produced from an unstable retrograde jet along the shelf break is studied from idealized numerical experiments with a primitive equation model. The jet is initially in thermal wind balance with a cross-isobath density gradient and is not subjected to any atmospheric forcing. Over the course of the model integration, the jet becomes unstable and produces a quasi-stationary eddy field over a 2-month period. During this period, the cross-slope flow at the shelf break is characterized by along-slope correlation scales of O(10) km and temporal correlation scales of a few days. The relative dispersion of parcels across isobaths is found to increase with time as tb, where 1 〈 b 〈 2. This mixed diffusive–ballistic regime appears to reflect the combined effects of (i) the short length scales of velocity correlation at the shelf break and (ii) the seaward excursion of monopolar and dipolar vortices. Cross-slope dispersion is greater offshore of the front than inshore of the front, as offshore parcels are both subducted onshore below density surfaces and translated offshore with eddies. Nonetheless, the exchange of parcels across the jet remains very limited on the monthly time scale. Particles originating from the bottom experience upward displacements of a few tens of meters and seaward displacements of O(100) km, suggesting that the eddy activity engendered by an unstable along-slope jet provides another mechanism for bottom boundary layer detachment near the shelf edge.
    Description: The author expresses his gratitude to the researchers who contributed to the development and public dissemination of POM [for a list of contributors, see Mellor (2002) and comments in the source code]. Discussions with Kenneth Brink, Hyodae Seo, and Weifeng Zhang have been helpful. Comments provided by Kenneth Brink on a draft are gratefully acknowledged. The criticism from two anonymous reviewers allowed us to better focus the manuscript and to significantly improve its clarity. This work has been supported by Grant OCE-1556400 from the U.S. National Science Foundation.
    Description: 2020-02-18
    Keywords: Dispersion ; Eddies ; Frontogenesis/frontolysis ; Instability ; Lagrangian circulation/transport ; Jets
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  • 185
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    Exploring lava-flow hazards at Pico Island, Azores Archipelago (Portugal) (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: Pico, the youngest island of the Azores Archipelago (Portugal), is characterized by a central volcano and a 30-km-long fissure zone. Its eruption rate is the highest of the Azores islands, with more than 35 eruptions in the last 2000 years. Here, we estimate the lava-flow hazard for Pico Island by combining the vent opening probability derived from the spatial distribution of eruptive fissures, the classes of expected eruptions inferred from the physical and chemical characteristics of historical eruptions, and the lava-flow paths simulated by the MAGFLOW model. The most likely area to host new eruptions is along a WNW–ESE trend centred on the central volcano, with the highest hazard affecting the two main residential zones of Lajes do Pico and Madalena. Our analysis is the first attempt to assess the lava-flow hazard for Pico Island, and may have important implications for decision-making in territorial management and future land-use planning.
    Description: Published
    Description: 156-161
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: lava flow hazard ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 186
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    Abrasive notches along the Atlantic Patagonian coast and their potential use as sea level markers: the case of Puerto Deseado (Santa Cruz, Argentina). (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2022-06-10
    Description: Patagonia Argentina is a key area for the study of sea level changes in the southern hemisphere, but the availability of reliable sea level markers in this area is still problematic. In fact the storm deposits (beach ridge) commonly used here to reconstruct past sea level oscillations introduce a wide error. Along the Puerto Deseado coast (Santa Cruz), morphometric analyses of 11 features were carried out using traditional measurement tools and a digital software-based method (tested on one selected feature) with the aim to investigate the possibility of their use as sea level markers. By undertaking accurate topographic profiles we identified the relationship between notches and current sea level. In detail, we identified two clusters of notch retreat point elevations, with a very low internal variability. The lower was located a little below the mean high tide level (mHT) and the upper located at least 0.5m above the maximum high tide level (MHT). Field observations of tidal levels and the position of notches suggest that the lower notches are active and the upper are inactive. This study on the abrasive notches attests their quality as sea level markers and opens up the use of fossil abrasive notches as palaeo sea level markers because the error linked to these features is substantially smaller than that introduced by beach ridges commonly used in the study area
    Description: Published
    Description: 1550 – 1558
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: restricted
    Keywords: notch; rocky coast; sea level marker; Patagonia; Argentina ; 01. Atmosphere::01.01. Atmosphere::01.01.02. Climate
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  • 187
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    Seismic structure beneath the Gulf of California: a contribution from group velocity measurements (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2022-06-14
    Description: Rayleigh wave group velocity dispersion measurements from local and regional earthquakes are used to interpret the lithospheric structure in the Gulf of California region. We compute group velocity maps for Rayleigh waves from 10 to 150 s using earthquakes recorded by broadband stations of the Network of Autonomously Recording Seismographs in Baja California and Mexico mainland, UNM in Mexico, BOR, DPP and GOR in southern California and TUC in Arizona. The study area is gridded in 120 longitude cells by 180 latitude cells, with an equal spacing of 10 × 10 km. Assuming that each gridpoint is laterally homogeneous, for each period the tomographic maps are inverted to produce a 3-D lithospheric shear wave velocity model for the region. Near the Gulf of California rift axis, we found three prominent low shear wave velocity regions, which are associated with mantle upwelling near the Cerro Prieto volcanic field, the Ballenas Transform Fault and the East Pacific Rise. Upwelling of the mantle at lithospheric and asthenospheric depths characterizes most of the Gulf. This more detailed finding is new when compared to previous surface wave studies in the region. A low-velocity zone in northcentral Baja at ∼28oN which extends east–south–eastwards is interpreted as an asthenospheric window. In addition, we also identify a well-defined high-velocity zone in the upper mantle beneath central-western Baja California, which correlates with the previously interpreted location of the stalled Guadalupe and Magdalena microplates. We interpret locations of the fossil slab and slab window in light of the distribution of unique post-subduction volcanic rocks in the Gulf of California and Baja California.We also observe a high-velocity anomaly at 50-km depth extending down to ∼130 km near the southwestern Baja coastline and beneath Baja, which may represent another remnant of the Farallon slab.
    Description: Published
    Description: 1861-1877
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: surface waves ; seismic tomography ; dynamics of lithosphere and mantle ; crustal structure ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
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  • 188
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    Measuring the north-south coseismic displacement component with high-resolution multi aperture InSAR (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: Earthquake source inversions based on space-borne Synthetic Aperture Radar interferometry (InSAR) are used extensively. Typically, however, only the line-of-sight (LoS) surface displacement component is measured, which is mainly sensitive to the vertical and E–W deformations, although well-established methods also exist to estimate the flight-path component, which is highly sensitive to the N–S displacement. With high-resolution sensors, these techniques are particularly appealing, because accuracies in the order of 3 cm can be achieved, while retaining spatial resolutions between 45 m and a few km, depending on the required level of filtering. We discuss the application to COSMO-SkyMed SAR imagery of the Spectral Diversity or Multi Aperture Interferometry technique, presenting the first SAR flight-path displacement field associated with the Mw 6.3, 2009 L’Aquila event (central Apennines). Finally, we observe and characterize a previously unknown misregistration pattern.
    Description: Published
    Description: 28-35
    Description: 2T. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: Crustal Deformation ; Multi Aperture Interferometry MAI ; InSAR ; L'Aquila Earthquake ; Satellite geodesy ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 189
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    3D displacement maps of the 2009 L'Aquila earthquake (Italy) by applying the SISTEM method to GPS and DiNSAR data (2015)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: We present an application of the novel SISTEM approach, to obtain the dense 3D ground deformation pattern produced by the April 6, 2009, Mw 6.3 L’Aquila earthquake. This event, characterized by a SW-dipping normal fault with thousands of foreshocks and aftershocks located in the depth range 5–15 km, is the most destructive to have struck the Abruzzo region since the major 1703 seismic sequence. The surface deformation, revealed by the SISTEM through the integration of GPS with interferometric measurements from the ENVISAT and ALOS satellites, shows a deformed area extending towards SE along the Aterno valley, in agreement with seismological and other geodetic observations. We inverted the SISTEM results using an optimization algorithm based on the genetic algorithm, providing an accurate spatial characterization of ground deformation. Our results improve previous kinematic solutions for the Paganica fault and allow identification of additional faults that have contributed to the observed complex ground deformation pattern.
    Description: Published
    Description: 79-85
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: JCR Journal
    Description: restricted
    Keywords: L'Aquila earthquake, SISTEM, GPS ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 190
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    Modelling the long-term deformation of the sedimentary substrate of Mt. Etna volcano (Italy) (2016)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: This study investigates in detail the deformation events that have affected the sedimentary successions forming the substrate of Mt. Etna volcano (Italy). Based on the geometric reconstruction of a buried sedimentary marker, we have been able to identify and quantify the effects of three different mechanisms of deformation that have affected the area in the last 600 ka. Numerical results from Finite Element Method (FEM) applied to model viscoelastic deformation suggest the occurrence of a crustal doming process originating at the mantle-crust transition (~16 km). We propose that the source of deformation is related to the diapiric uprise of hydrothermal material originating in altered ocean-like crust and its emplacement at a shallower level in the crust. This process has great relevance in the volcanic system and should be considered for the full assessment of its origin and evolution.
    Description: Published
    Description: 338 – 345
    Description: 4V. Vulcani e ambiente
    Description: JCR Journal
    Description: restricted
    Keywords: volcanic doming ; viscoelastic modeling ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
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  • 191
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    Evidence of a shallow magma intrusion beneath the NE Rift system of Mt. Etna during 2013 (2017)
    Wiley-Blackwell
    Details
    Publication Date: 2022-05-24
    Description: Continuous GPS (CGPS) data, collected at Mt. Etna between April 2012 and October 2013, clearly define inflation/deflation processes typically observed before/after an eruption onset. During the inflationary process from May to October 2013, a particular deformation pattern localised in the upper North Eastern sector of the volcano suggests that a magma intrusion had occurred a few km away from the axis of the summit craters, beneath the NE Rift system. This is the first time that this pattern has been recorded by CGPS data at Mt. Etna. We believe that this inflation process might have taken place periodically at Mt. Etna and might be associated with the intrusion of batches of magma that are separate from the main feeding system. We provide a model to explain this unusual behaviour and the eruptive regime of this rift zone, which is characterised by long periods of quiescence followed by often dangerous eruptions in which vents can open at low elevation and thus threaten the villages in this sector of the volcano.
    Description: Published
    Description: 356-363
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Shallow intrusion beneath NE Rift system ; Mt. Etna volcano ; CGPS data ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 192
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    Properties and origins of the anisotropic eddy-induced transport in the North Atlantic (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 778–791, doi:10.1175/JPO-D-14-0164.1.
    Description: This study examines anisotropic transport properties of the eddying North Atlantic flow, using an idealized model of the double-gyre oceanic circulation and altimetry-derived velocities. The material transport by the time-dependent flow (quantified by the eddy diffusivity tensor) varies geographically and is anisotropic, that is, it has a well-defined direction of the maximum transport. One component of the time-dependent flow, zonally elongated large-scale transients, is particularly important for the anisotropy, as it corresponds to primarily zonal material transport and long correlation time scales. The importance of these large-scale zonal transients in the material distribution is further confirmed with simulations of idealized color dye tracers, which has implications for parameterizations of the eddy transport in non-eddy-resolving models.
    Description: IK would like to acknowledge support through the NSF Grant OCE-1154923. IR was supported by the NSF OCE-1154641 and NASA Grant NNX14AH29G.
    Description: 2015-09-01
    Keywords: Circulation/ Dynamics ; Eddies ; Lagrangian circulation/transport ; Mesoscale processes ; Ocean circulation ; Models and modeling ; Tracers
    Repository Name: Woods Hole Open Access Server
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  • 193
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    Internal waves and mixing near the Kerguelen Plateau (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 417-437, doi:10.1175/JPO-D-15-0055.1.
    Description: In the stratified ocean, turbulent mixing is primarily attributed to the breaking of internal waves. As such, internal waves provide a link between large-scale forcing and small-scale mixing. The internal wave field north of the Kerguelen Plateau is characterized using 914 high-resolution hydrographic profiles from novel Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats. Altogether, 46 coherent features are identified in the EM-APEX velocity profiles and interpreted in terms of internal wave kinematics. The large number of internal waves analyzed provides a quantitative framework for characterizing spatial variations in the internal wave field and for resolving generation versus propagation dynamics. Internal waves observed near the Kerguelen Plateau have a mean vertical wavelength of 200 m, a mean horizontal wavelength of 15 km, a mean period of 16 h, and a mean horizontal group velocity of 3 cm s−1. The internal wave characteristics are dependent on regional dynamics, suggesting that different generation mechanisms of internal waves dominate in different dynamical zones. The wave fields in the Subantarctic/Subtropical Front and the Polar Front Zone are influenced by the local small-scale topography and flow strength. The eddy-wave field is influenced by the large-scale flow structure, while the internal wave field in the Subantarctic Zone is controlled by atmospheric forcing. More importantly, the local generation of internal waves not only drives large-scale dissipation in the frontal region but also downstream from the plateau. Some internal waves in the frontal region are advected away from the plateau, contributing to mixing and stratification budgets elsewhere.
    Description: A.M. was supported by the joint CSIRO-University of Tasmania Quantitative Marine Science (QMS) program and the 2009 CSIRO Wealth from Ocean Flagship Collaborative Fund. K.L.P.’s salary support was provided by Woods Hole Oceanographic Institution bridge support funds. B.M.S. was supported by the Australian Climate Change Science Program.
    Description: 2016-06-07
    Keywords: Geographic location/entity ; Southern Ocean ; Circulation/ Dynamics ; Internal waves ; Mixing ; Wave properties ; Observational techniques and algorithms ; In situ oceanic observations ; Profilers, oceanic
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  • 194
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    Continental shelf baroclinic instability. Part II : oscillating wind forcing (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 569-582, doi:10.1175/JPO-D-15-0048.1.
    Description: Continental shelf baroclinic instability energized by fluctuating alongshore winds is treated using idealized primitive equation numerical model experiments. A spatially uniform alongshore wind, sinusoidal in time, alternately drives upwelling and downwelling and so creates highly variable, but slowly increasing, available potential energy. For all of the 30 model runs, conducted with a wide range of parameters (varying Coriolis parameter, initial stratification, bottom friction, forcing period, wind strength, and bottom slope), a baroclinic instability and subsequent eddy field develop. Model results and scalings show that the eddy kinetic energy increases with wind amplitude, forcing period, stratification, and bottom slope. The dominant alongshore length scale of the eddy field is essentially an internal Rossby radius of deformation. The resulting depth-averaged alongshore flow field is dominated by the large-scale, periodic wind forcing, while the cross-shelf flow field is dominated by the eddy variability. The result is that correlation length scales for alongshore flow are far greater than those for cross-shelf velocity. This scale discrepancy is qualitatively consistent with midshelf observations by Kundu and Allen, among others.
    Description: This work was funded by the Woods Hole Oceanographic Institution and by the National Science Foundation, Physical Oceanography section through Grant OCE-1433953.
    Description: 2016-06-09
    Keywords: Geographic location/entity ; Continental shelf/slope ; Variability ; Oceanic variability
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    The Arctic Ocean spices up (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1277-1284, doi:10.1175/JPO-D-16-0027.1.
    Description: The contemporary Arctic Ocean differs markedly from midlatitude, ice-free, and relatively warm oceans in the context of density-compensating temperature and salinity variations. These variations are invaluable tracers in the midlatitudes, revealing essential fundamental physical processes of the oceans, on scales from millimeters to thousands of kilometers. However, in the cold Arctic Ocean, temperature variations have little effect on density, and a measure of density-compensating variations in temperature and salinity (i.e., spiciness) is not appropriate. In general, temperature is simply a passive tracer, which implies that most of the heat transported in the Arctic Ocean relies entirely on the ocean dynamics determined by the salinity field. It is shown, however, that as the Arctic Ocean warms up, temperature will take on a new role in setting dynamical balances. Under continued warming, there exists the possibility for a regime shift in the mechanisms by which heat is transported in the Arctic Ocean. This may result in a cap on the storage of deep-ocean heat, having profound implications for future predictions of Arctic sea ice.
    Description: Support was provided by the National Science Foundation Division of Polar Programs Award 1350046 and Office of Naval Research Grant Number N00014-12-1-0110.
    Description: 2016-10-05
    Keywords: Geographic location/entity ; Arctic ; Circulation/ Dynamics ; Ocean dynamics
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  • 196
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    Seasonal and interannual variations of Irminger ring formation and boundary–interior heat exchange in FLAME (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1717-1734, doi:10.1175/JPO-D-15-0124.1.
    Description: The contribution of warm-core anticyclones shed by the Irminger Current off West Greenland, known as Irminger rings, to the restratification of the upper layers of the Labrador Sea is investigated in the 1/12° Family of Linked Atlantic Models Experiment (FLAME) model. The model output, covering the 1990–2004 period, shows strong similarities to observations of the Irminger Current as well as ring observations at a mooring located offshore of the eddy formation region in 2007–09. An analysis of fluxes in the model shows that while the majority of heat exchange with the interior indeed occurs at the site of the Irminger Current instability, the contribution of the coherent Irminger rings is modest (18%). Heat is provided to the convective region mainly through noncoherent anomalies and enhanced local mixing by the rings facilitating further exchange between the boundary and interior. The time variability of the eddy kinetic energy and the boundary to interior heat flux in the model are strongly correlated to the density gradient between the dense convective region and the more buoyant boundary current. In FLAME, the density variations of the boundary current are larger than those of the convective region, thereby largely controlling changes in lateral fluxes. Synchronous long-term trends in temperature in the boundary and the interior over the 15-yr simulation suggest that the heat flux relative to the temperature of the interior is largely steady on these time scales.
    Description: The authors were supported in this work by the U.S. National Science Foundation.
    Keywords: Geographic location/entity ; North Atlantic Ocean ; Circulation/ Dynamics ; Anticyclones ; Boundary currents ; Convection ; Eddies ; Fluxes
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  • 197
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    Satellite-derived ocean thermal structure for the North Atlantic hurricane season (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Monthly Weather Review 144 (2016): 877-896, doi:10.1175/MWR-D-15-0275.1.
    Description: This paper describes a new model (method) called Satellite-derived North Atlantic Profiles (SNAP) that seeks to provide a high-resolution, near-real-time ocean thermal field to aid tropical cyclone (TC) forecasting. Using about 139 000 observed temperature profiles, a spatially dependent regression model is developed for the North Atlantic Ocean during hurricane season. A new step introduced in this work is that the daily mixed layer depth is derived from the output of a one-dimensional Price–Weller–Pinkel ocean mixed layer model with time-dependent surface forcing. The accuracy of SNAP is assessed by comparison to 19 076 independent Argo profiles from the hurricane seasons of 2011 and 2013. The rms differences of the SNAP-estimated isotherm depths are found to be 10–25 m for upper thermocline isotherms (29°–19°C), 35–55 m for middle isotherms (18°–7°C), and 60–100 m for lower isotherms (6°–4°C). The primary error sources include uncertainty of sea surface height anomaly (SSHA), high-frequency fluctuations of isotherm depths, salinity effects, and the barotropic component of SSHA. These account for roughly 29%, 25%, 19%, and 10% of the estimation error, respectively. The rms differences of TC-related ocean parameters, upper-ocean heat content, and averaged temperature of the upper 100 m, are ~10 kJ cm−2 and ~0.8°C, respectively, over the North Atlantic basin. These errors are typical also of the open ocean underlying the majority of TC tracks. Errors are somewhat larger over regions of greatest mesoscale variability (i.e., the Gulf Stream and the Loop Current within the Gulf of Mexico).
    Description: IFP is supported by Grants NSC 101-2628-M-002-001-MY4 and MOST 103-2111-M-002 -002 -MY3. JFP and SRJ were supported by the U.S. Office of Naval Research under the project “Impact of Typhoons on the North Pacific, ITOP.”
    Description: 2016-06-08
    Keywords: Atm/Ocean Structure/ Phenomena ; Atmosphere-ocean interaction ; Oceanic mixed layer ; Tropical cyclones ; Observational techniques and algorithms ; Satellite observations
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 198
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    Exploring practical estimates of the ensemble size necessary for particle filters (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Monthly Weather Review 144 (2016): 861-875, doi:10.1175/MWR-D-14-00303.1.
    Description: Particle filtering methods for data assimilation may suffer from the “curse of dimensionality,” where the required ensemble size grows rapidly as the dimension increases. It would, therefore, be useful to know a priori whether a particle filter is feasible to implement in a given system. Previous work provides an asymptotic relation between the necessary ensemble size and an exponential function of , a statistic that depends on observation-space quantities and that is related to the system dimension when the number of observations is large; for linear, Gaussian systems, the statistic can be computed from eigenvalues of an appropriately normalized covariance matrix. Tests with a low-dimensional system show that these asymptotic results remain useful when the system is nonlinear, with either the standard or optimal proposal implementation of the particle filter. This study explores approximations to the covariance matrices that facilitate computation in high-dimensional systems, as well as different methods to estimate the accumulated system noise covariance for the optimal proposal. Since may be approximated using an ensemble from a simpler data assimilation scheme, such as the ensemble Kalman filter, the asymptotic relations thus allow an estimate of the ensemble size required for a particle filter before its implementation. Finally, the improved performance of particle filters with the optimal proposal, relative to those using the standard proposal, in the same low-dimensional system is demonstrated.
    Description: Slivinski was supported by the NSF through Grants DMS-0907904 and DMS-1148284, by ONR through DOD (MURI) Grant N000141110087, and by NCAR’s Advanced Study Program during a collaborative visit to NCAR.
    Description: 2016-05-11
    Keywords: Mathematical and statistical techniques ; Statistical techniques ; Models and modeling ; Data assimilation ; Ensembles ; Nonlinear models
    Repository Name: Woods Hole Open Access Server
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  • 199
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    Observations of the transfer of energy and momentum to the oceanic surface boundary layer beneath breaking waves (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 1823-1837, doi:10.1175/JPO-D-15-0165.1.
    Description: Measurements just beneath the ocean surface demonstrate that the primary mechanism by which energy from breaking waves is transmitted into the water column is through the work done by the covariance of turbulent pressure and velocity fluctuations. The convergence in the vertical transport of turbulent kinetic energy (TKE) balances the dissipation rate of TKE at first order and is nearly an order of magnitude greater than the sum of the integrated Eulerian and Stokes shear production. The measured TKE transport is consistent with a simple conceptual model that assumes roughly half of the surface flux of TKE by wave breaking is transmitted to depths greater than the significant wave height. During conditions when breaking waves are inferred, the direction of momentum flux is more aligned with the direction of wave propagation than with the wind direction. Both the energy and momentum fluxes occur at frequencies much lower than the wave band, consistent with the time scales associated with wave breaking. The largest instantaneous values of momentum flux are associated with strong downward vertical velocity perturbations, in contrast to the pressure work, which is associated with strong drops in pressure and upward vertical velocity perturbations.
    Description: Funding for this research was provided by the National Science Foundation Grants OCE-1339032 and OCE-1338518
    Keywords: Circulation/ Dynamics ; Energy transport ; Mixing ; Momentum ; Turbulence ; Wave breaking ; Waves, oceanic
    Repository Name: Woods Hole Open Access Server
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  • 200
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    Remote sensing of the surface wind field over the coastal ocean via direct calibration of HF radar backscatter power (2016)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 33 (2016): 1377-1392, doi:10.1175/JTECH-D-15-0242.1.
    Description: The calibration and validation of a novel approach to remotely sense surface winds using land-based high-frequency (HF) radar systems are described. Potentially available on time scales of tens of minutes and spatial scales of 2–3 km for wide swaths of the coastal ocean, HF radar–based surface wind observations would greatly aid coastal ocean planners, researchers, and operational stakeholders by providing detailed real-time estimates and climatologies of coastal winds, as well as enabling higher-quality short-term forecasts of the spatially dependent wind field. Such observations are particularly critical for the developing offshore wind energy community. An autonomous surface vehicle was deployed within the Massachusetts Wind Energy Area, located south of Martha’s Vineyard, Massachusetts, for one month, collecting wind observations that were used to test models of wind-wave spreading and HF radar energy loss, thereby empirically relating radar-measured power to surface winds. HF radar–based extractions of the remote wind speed had accuracies of 1.4 m s−1 for winds less than 7 m s−1, within the optimal range of the radar frequency used. Accuracies degraded at higher winds due to low signal-to-noise ratios in the returned power and poor resolution of the model. Pairing radar systems with a range of transmit frequencies with adjustments of the extraction model for additional power and environmental factors would resolve many of the errors observed.
    Description: This analysis was supported by the Massachusetts Clean Energy Center. The HF radar data used were obtained during projects supported by the National Science Foundation, the NOAA Integrated Ocean Observing System (IOOS), and internal funds from the Woods Hole Oceanographic Institution.
    Description: 2016-12-24
    Keywords: Atm/Ocean Structure/ Phenomena ; Wind ; Observational techniques and algorithms ; Algorithms ; In situ oceanic observations ; Radars/Radar observations ; Remote sensing ; Surface observations
    Repository Name: Woods Hole Open Access Server
    Type: Article
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