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  • American Meteorological Society
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  • 101
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 43 (2013): 283–300, doi:10.1175/JPO-D-11-0240.1.
    Description: Motivated by the recent interest in ocean energetics, the widespread use of horizontal eddy viscosity in models, and the promise of high horizontal resolution data from the planned wide-swath satellite altimeter, this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence, with a particular focus on spectral kinetic energy fluxes Π(K) computed in the isotropic wavenumber (K) domain. The paper utilizes idealized two-layer quasigeostrophic (QG) models, realistic high-resolution ocean general circulation models, and present-generation gridded satellite altimeter data. Adding horizontal eddy viscosity to the QG model results in a forward cascade at smaller scales, in apparent agreement with results from present-generation altimetry. Eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies. Filtering the output of either the QG or realistic models before computing Π(K) also greatly increases the forward cascade. Such filtering mimics the smoothing inherent in the construction of present-generation gridded altimeter data. It is therefore difficult to say whether the forward cascades seen in present-generation altimeter data are due to real physics (represented here by eddy viscosity) or to insufficient horizontal resolution. The inverse cascade at larger scales remains in the models even after filtering, suggesting that its existence in the models and in altimeter data is robust. However, the magnitude of the inverse cascade is affected by filtering, suggesting that the wide-swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller-scale dynamics.
    Description: BKA received support from Office of Naval Research Grant N00014-11-1-0487, National Science Foundation (NSF) Grants OCE-0924481 and OCE- 09607820, and University of Michigan startup funds. KLP acknowledges support from Woods Hole Oceanographic Institution bridge support funds. RBS acknowledges support from NSF grants OCE-0960834 and OCE-0851457, a contract with the National Oceanography Centre, Southampton, and a NASA subcontract to Boston University. JFS and JGR were supported by the projects ‘‘Global and remote littoral forcing in global ocean models’’ and ‘‘Agesotrophic vorticity dynamics of the ocean,’’ respectively, both sponsored by the Office of Naval Research under program element 601153N.
    Description: 2013-08-01
    Keywords: Eddies ; Nonlinear dynamics ; Ocean dynamics ; Satellite observations ; Ocean models
    Repository Name: Woods Hole Open Access Server
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  • 102
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 43 (2013): 744–765, doi:10.1175/JPO-D-12-067.1.
    Description: This study investigates the coherence between ocean bottom pressure signals at the Rapid Climate Change programme (RAPID) West Atlantic Variability Experiment (WAVE) array on the western North Atlantic continental slope, including the Woods Hole Oceanographic Institution Line W. Highly coherent pressure signals propagate southwestward along the slope, at speeds in excess of 128 m s−1, consistent with expectations of barotropic Kelvin-like waves. Coherent signals are also evidenced in the smaller pressure differences relative to 1000-m depth, which are expected to be associated with depth-dependent basinwide meridional transport variations or an overturning circulation. These signals are coherent and almost in phase for all time scales from 3.6 years down to 3 months. Coherence is still seen at shorter time scales for which group delay estimates are consistent with a propagation speed of about 1 m s−1 over 990 km of continental slope but with large error bounds on the speed. This is roughly consistent with expectations for propagation of coastally trapped waves, though somewhat slower than expected. A comparison with both Eulerian currents and Lagrangian float measurements shows that the coherence is inconsistent with a propagation of signals by advection, except possibly on time scales longer than 6 months.
    Description: This work was funded by the U.K. Natural Environment Research Council. Sofia Olhede was supported by EPSRC Grant EP/I005250/1. Initial observations at StationW(2001–04) were made possible by a grant from the G. Unger Vetlesen Foundation and support from the Woods Hole Oceanographic Institution. Since 2004, the Line W program has been supported by the U.S. National Science Foundation with supplemental contribution from WHOIs Ocean and Climate Change Institute.
    Description: 2013-10-01
    Keywords: Atlantic Ocean ; Boundary currents ; Meridional overturning circulation ; Pressure ; Waves, oceanic ; In situ oceanic observations
    Repository Name: Woods Hole Open Access Server
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  • 103
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 26 (2013): 2453–2466, doi:10.1175/JCLI-D-12-00023.1.
    Description: The North Atlantic Oscillation (NAO) is one of the most important modes of variability in the global climate system and is characterized by a meridional dipole in the sea level pressure field, with centers of action near Iceland and the Azores. It has a profound influence on the weather, climate, ecosystems, and economies of Europe, Greenland, eastern North America, and North Africa. It has been proposed that around 1980, there was an eastward secular shift in the NAO’s northern center of action that impacted sea ice export through Fram Strait. Independently, it has also been suggested that the location of its southern center of action is tied to the phase of the NAO. Both of these attributes of the NAO have been linked to anthropogenic climate change. Here the authors use both the one-point correlation map technique as well as empirical orthogonal function (EOF) analysis to show that the meridional dipole that is often seen in the sea level pressure field over the North Atlantic is not purely the result of the NAO (as traditionally defined) but rather arises through an interplay among the NAO and two other leading modes of variability in the North Atlantic region: the East Atlantic (EA) and the Scandinavian (SCA) patterns. This interplay has resulted in multidecadal mobility in the two centers of action of the meridional dipole since the late nineteenth century. In particular, an eastward movement of the dipole has occurred during the 1930s to 1950s as well as more recently. This mobility is not seen in the leading EOF of the sea level pressure field in the region.
    Description: GWKM was supported by the Natural Sciences and Engineering Research Council of Canada. IAR was supported in part by NE/C003365/1. RSP was supported by Grant OCE-0959381 from the U.S. National Science Foundation.
    Description: 2013-10-15
    Keywords: North Atlantic Ocean ; North Atlantic Oscillation ; Climate variability ; Climatology ; Empirical orthogonal functions
    Repository Name: Woods Hole Open Access Server
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  • 104
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. 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 42 (2012): 2234–2253, doi:10.1175/JPO-D-12-033.1.
    Description: Meridional velocity, mass, and heat transport in the equatorial oceans are difficult to estimate because of the nonapplicability of the geostrophic balance. For this purpose a steady-state model is utilized in the equatorial Indian Ocean using NCEP wind stress and temperature and salinity data from the World Ocean Atlas 2005 (WOA05) and Argo. The results show a Somali Current flowing to the south during the winter monsoon carrying −11.5 ± 1.3 Sv (1 Sv ≡ 106 m3 s−1) and −12.3 ± 0.3 Sv from WOA05 and Argo, respectively. In the summer monsoon the Somali Current reverses to the north transporting 16.8 ± 1.2 Sv and 19.8 ± 0.6 Sv in the WOA05 and Argo results. Transitional periods are considered together and in consequence, there is not a clear Somali Current present in this period. Model results fit with in situ measurements made around the region, although Argo data results are quite more realistic than WOA05 data results.
    Description: This study has been partly funded by the MOC Project (CTM 2008- 06438) and the Spanish contribution to the Argo network (AC2009 ACI2009-0998), financed by the Spanish Government and Feder.
    Description: 2013-06-01
    Keywords: Indian Ocean ; Subtropics ; Currents ; Ocean circulation ; Transport ; Wind stress
    Repository Name: Woods Hole Open Access Server
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  • 105
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 43 (2013): 2132–2141, doi:10.1175/JPO-D-12-0182.1.
    Description: Repeated occupations of two hydrographic sections in the southwest Pacific basin from the 1990s to 2000s track property changes of Antarctic Bottom Water (AABW). The largest property changes—warming, freshening, increase in total carbon, and decrease in oxygen—are found near the basin’s deep western boundary between 50° and 20°S. The magnitude of the property changes decreases with increasing distance from the western boundary. At the deep western boundary, analysis of the relative importance of AABW (γn 〉 28.1 kg m−3) freshening, heating, or isopycnal heave suggests that the deep ocean stratification change is the result of both warming and freshening processes. The consistent deep ocean changes near the western boundary of the southwest Pacific basin dispel the notion that the deep ocean is quiescent. High-latitude climate variability is being directly transmitted into the deep southwest Pacific basin and the global deep ocean through dynamic deep western boundary currents.
    Description: BMS, SEW, and BT were supported by the Australian Climate Change Science Program, funded jointly by the Department of Climate Change and Energy Efficiency and CSIRO. Funding for AM was provided through NOAA GrantNA110AR4310063.
    Description: 2014-04-01
    Keywords: Circulation/ Dynamics ; Waves ; Oceanic
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  • 106
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 43 (2013): 1589–1610, doi:10.1175/JPO-D-12-0173.1.
    Description: This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s−1) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient α in the COARE algorithm is modified to , where m = 0.017 m−1 s and b = −0.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13 m s−1. Wave age– and wave slope–dependent parameterizations of the surface roughness are also investigated, but the COARE 3.5 wind speed–dependent formulation matches the observations well without any wave information. The available data provide a simple reason for why wind speed–, wave age–, and wave slope–dependent formulations give similar results—the inverse wave age varies nearly linearly with wind speed in long-fetch conditions for wind speeds up to 25 m s−1.
    Description: This work was funded by the National Science Foundation Grant OCE04-24536 as part of the CLIVAR Mode Water Dynamics Experiment (CLIMODE) and the Office of Naval Research Grant N00014-05-1-0139 as part of the CBLAST-LOW program.
    Description: 2014-02-01
    Keywords: Wind shear ; Wind stress ; Atmosphere-ocean interaction ; Fluxes ; Momentum ; Algorithms
    Repository Name: Woods Hole Open Access Server
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  • 107
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 30 (2013): 1767–1788, doi:10.1175/JTECH-D-12-00140.1.
    Description: Seismic images of oceanic thermohaline finestructure record vertical displacements from internal waves and turbulence over large sections at unprecedented horizontal resolution. Where reflections follow isopycnals, their displacements can be used to estimate levels of turbulence dissipation, by applying the Klymak–Moum slope spectrum method. However, many issues must be considered when using seismic images for estimating turbulence dissipation, especially sources of random and harmonic noise. This study examines the utility of seismic images for estimating turbulence dissipation in the ocean, using synthetic modeling and data from two field surveys, from the South China Sea and the eastern Pacific Ocean, including the first comparison of turbulence estimates from seismic images and from vertical shear. Realistic synthetic models that mimic the spectral characteristics of internal waves and turbulence show that reflector slope spectra accurately reproduce isopycnal slope spectra out to horizontal wavenumbers of 0.04 cpm, corresponding to horizontal wavelengths of 25 m. Using seismic reflector slope spectra requires recognition and suppression of shot-generated harmonic noise and restriction of data to frequency bands with signal-to-noise ratios greater than about 4. Calculation of slope spectra directly from Fourier transforms of the seismic data is necessary to determine the suitability of a particular dataset to turbulence estimation from reflector slope spectra. Turbulence dissipation estimated from seismic reflector displacements compares well to those from 10-m shear determined by coincident expendable current profiler (XCP) data, demonstrating that seismic images can produce reliable estimates of turbulence dissipation in the ocean, provided that random noise is minimal and harmonic noise is removed.
    Description: This work was funded by NSF Grants 0452744, 0405654, and 0648620, and ONR/DEPSCoR Grant DODONR40027.
    Description: 2014-02-01
    Keywords: Mixing ; Thermocline ; Acoustic measurements/effects
    Repository Name: Woods Hole Open Access Server
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  • 108
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 94 (2013): 1131–1144, doi:10.1175/BAMS-D-12-00100.1.
    Description: The recent retreat and speedup of outlet glaciers, as well as enhanced surface melting around the ice sheet margin, have increased Greenland's contribution to sea level rise to 0.6 ± 0.1 mm yr−1 and its discharge of freshwater into the North Atlantic. The widespread, near-synchronous glacier retreat, and its coincidence with a period of oceanic and atmospheric warming, suggests a common climate driver. Evidence points to the marine margins of these glaciers as the region from which changes propagated inland. Yet, the forcings and mechanisms behind these dynamic responses are poorly understood and are either missing or crudely parameterized in climate and ice sheet models. Resulting projected sea level rise contributions from Greenland by 2100 remain highly uncertain. This paper summarizes the current state of knowledge and highlights key physical aspects of Greenland's coupled ice sheet–ocean–atmosphere system. Three research thrusts are identified to yield fundamental insights into ice sheet, ocean, sea ice, and atmosphere interactions, their role in Earth's climate system, and probable trajectories of future changes: 1) focused process studies addressing critical glacier, ocean, atmosphere, and coupled dynamics; 2) sustained observations at key sites; and 3) inclusion of relevant dynamics in Earth system models. Understanding the dynamic response of Greenland's glaciers to climate forcing constitutes both a scientific and technological frontier, given the challenges of obtaining the appropriate measurements from the glaciers' marine termini and the complexity of the dynamics involved, including the coupling of the ocean, atmosphere, glacier, and sea ice systems. Interdisciplinary and international cooperation are crucial to making progress on this novel and complex problem.
    Description: 2014-02-01
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  • 109
    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): 842–854, doi:10.1175/JTECH-D-14-00215.1.
    Description: The time and space variability of wave transformation through a tidal inlet is investigated with radar remote sensing. The frequency of wave breaking and the net wave breaking dissipation at high spatial resolution is estimated using image sequences acquired with a land-based X-band marine radar. Using the radar intensity data, transformed to normalized radar cross section σ0, the temporal and spatial distributions of wave breaking are identified using a threshold developed via the data probability density function. In addition, the inlet bathymetry is determined via depth inversion of the radar-derived frequencies and wavenumbers of the surface waves using a preexisting algorithm (cBathy). Wave height transformation is calculated through the 1D cross-shore energy flux equation incorporating the radar-estimated breaking distribution and bathymetry. The accuracy of the methodology is tested by comparison with in situ wave height observations over a 9-day period, obtaining correlation values R = 0.68 to 0.96, and root-mean-square errors from 0.05 to 0.19 m. Predicted wave forcing, computed as the along-inlet gradient of the cross-shore radiation stress was onshore during high-wave conditions, in good agreement (R = 0.95) with observations.
    Description: These data were collected as part of a joint field program, Data Assimilation and Remote Sensing for Littoral Applications (DARLA) and Rivers and Inlets (RIVET-1), both funded by the Office of Naval Research. The authors were funded through the Office of Naval Research Grant N00014-10-1-0932 and the Office of the Assistant Secretary of Defense for Research and Engineering.
    Description: 2015-10-01
    Keywords: Wave breaking ; Waves, oceanic ; Wind waves ; In situ oceanic observations ; Radars/Radar observations ; Remote sensing
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  • 110
    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): 2006–2024, doi:10.1175/JPO-D-14-0234.1.
    Description: The effects of wind-driven whitecapping on the evolution of the ocean surface boundary layer are examined using an idealized one-dimensional Reynolds-averaged Navier–Stokes numerical model. Whitecapping is parameterized as a flux of turbulent kinetic energy through the sea surface and through an adjustment of the turbulent length scale. Simulations begin with a two-layer configuration and use a wind that ramps to a steady stress. This study finds that the boundary layer begins to thicken sooner in simulations with whitecapping than without because whitecapping introduces energy to the base of the boundary layer sooner than shear production does. Even in the presence of whitecapping, shear production becomes important for several hours, but then inertial oscillations cause shear production and whitecapping to alternate as the dominant energy sources for mixing. Details of these results are sensitive to initial and forcing conditions, particularly to the turbulent length scale imposed by breaking waves and the transfer velocity of energy from waves to turbulence. After 1–2 days of steady wind, the boundary layer in whitecapping simulations has thickened more than the boundary layer in simulations without whitecapping by about 10%–50%, depending on the forcing and initial conditions.
    Description: We thank Skidmore College for financial and infrastructure support, and Skidmore and the National Science Foundation for funding travel to meetings where early versions of this work were presented. We also thank the National Science Foundation, Oregon State University, Jonathan Nash, and Joe Jurisa for funding and hosting a workshop on River Plume Mixing in October, 2013, where ideas and context for this paper were developed.
    Description: 2016-02-01
    Keywords: Circulation/ Dynamics ; Mixing ; Turbulence ; Wave breaking ; Wind stress ; Atm/Ocean Structure/ Phenomena ; Mixed layer
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  • 111
    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): 8574–8584, doi:10.1175/JCLI-D-14-00809.1.
    Description: The subsurface ocean response to anthropogenic climate forcing remains poorly characterized. From the Coupled Model Intercomparison Project (CMIP), a robust response of the lower thermocline is identified, where the warming is considerably weaker in the subtropics than in the tropics and high latitudes. The lower thermocline change is inversely proportional to the thermocline depth in the present climatology. Ocean general circulation model (OGCM) experiments show that sea surface warming is the dominant forcing for the subtropical gyre change in contrast to natural variability for which wind dominates, and the ocean response is insensitive to the spatial pattern of surface warming. An analysis based on a ventilated thermocline model shows that the pattern of the lower thermocline change can be interpreted in terms of the dynamic response to the strengthened stratification and downward heat mixing. Consequently, the subtropical gyres become intensified at the surface but weakened in the lower thermcline, consistent with results from CMIP experiments.
    Description: The work was supported by the National Basic Research Program of China (2012CB955600), the National Natural Science Foundation of China (41125019, 41206021), and the U.S. National Science Foundation (AGS 1249145, 1305719).
    Description: 2016-05-01
    Keywords: Circulation/ Dynamics ; Ocean circulation ; Physical Meteorology and Climatology ; Climate change
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  • 112
    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): 3829-3852, doi:10.1175/JCLI-D-16-0479.1.
    Description: This study provides an assessment of the uncertainty in ocean surface (OS) freshwater budgets and variability using evaporation E and precipitation P from 10 atmospheric reanalyses, two combined satellite-based E − P products, and two observation-based salinity products. Three issues are examined: the uncertainty level in the OS freshwater budget in atmospheric reanalyses, the uncertainty structure and association with the global ocean wet/dry zones, and the potential of salinity in ascribing the uncertainty in E − P. The products agree on the global mean pattern but differ considerably in magnitude. The OS freshwater budgets are 129 ± 10 (8%) cm yr−1 for E, 118 ± 11 (9%) cm yr−1 for P, and 11 ± 4 (36%) cm yr−1 for E − P, where the mean and error represent the ensemble mean and one standard deviation of the ensemble spread. The E − P uncertainty exceeds the uncertainty in E and P by a factor of 4 or more. The large uncertainty is attributed to P in the tropical wet zone. Most reanalyses tend to produce a wider tropical rainband when compared to satellite products, with the exception of two recent reanalyses that implement an observation-based correction for the model-generated P over land. The disparity in the width and the extent of seasonal migrations of the tropical wet zone causes a large spread in P, implying that the tropical moist physics and the realism of tropical rainfall remain a key challenge. Satellite salinity appears feasible to evaluate the fidelity of E − P variability in three tropical areas, where the uncertainty diagnosis has a global indication.
    Description: Primary support for the study is provided by the NOAAModeling, Analysis, Predictions, and Projections (MAPP) Program’s Climate Reanalysis Task Force (CRTF) through Grant NA13OAR4310106.
    Description: 2017-11-02
    Keywords: Hydrologic cycle ; Precipitation ; Evaporation ; Salinity ; Water budget ; Reanalysis data
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  • 113
    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): 1233-1243, doi:10.1175/JCLI-D-16-0496.1.
    Description: A downscaling approach is applied to future projection simulations from four CMIP5 global climate models to investigate the response of the tropical cyclone (TC) climatology over the North Pacific basin to global warming. Under the influence of the anthropogenic rise in greenhouse gases, TC-track density, power dissipation, and TC genesis exhibit robust increasing trends over the North Pacific, especially over the central subtropical Pacific region. The increase in North Pacific TCs is primarily manifested as increases in the intense and relatively weak TCs. Examination of storm duration also reveals that TCs over the North Pacific have longer lifetimes under global warming. Through a genesis potential index, the mechanistic contributions of various physical climate factors to the simulated change in TC genesis are explored. More frequent TC genesis under global warming is mostly attributable to the smaller vertical wind shear and greater potential intensity (primarily due to higher sea surface temperature). In contrast, the effect of the saturation deficit of the free troposphere tends to suppress TC genesis, and the change in large-scale vorticity plays a negligible role.
    Description: The authors acknowledge support from the Strategic Environmental Research and Development Program (SERDP) (RC-2336). SERDP is the environmental science and technology program of the U.S. Department of Defense (DoD) in partnership with the U.S. Department of Energy (DOE) and the U.S. Environmental Protection Agency (EPA).
    Description: 2017-08-01
    Keywords: Tropical cyclones
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  • 114
    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): 1739-1751, doi:10.1175/JCLI-D-16-0200.1.
    Description: The Indian Ocean has sustained robust surface warming in recent decades, but the role of multidecadal variability remains unclear. Using ocean model hindcasts, characteristics of low-frequency Indian Ocean temperature variations are explored. Simulated upper-ocean temperature changes across the Indian Ocean in the hindcast are consistent with those recorded in observational products and ocean reanalyses. Indian Ocean temperatures exhibit strong warming trends since the 1950s limited to the surface and south of 30°S, while extensive subsurface cooling occurs over much of the tropical Indian Ocean. Previous work focused on diagnosing causes of these long-term trends in the Indian Ocean over the second half of the twentieth century. Instead, the temporal evolution of Indian Ocean subsurface heat content is shown here to reveal distinct multidecadal variations associated with the Pacific decadal oscillation, and the long-term trends are thus interpreted to result from aliasing of the low-frequency variability. Transmission of the multidecadal signal occurs via an oceanic pathway through the Indonesian Throughflow and is manifest across the Indian Ocean centered along 12°S as westward-propagating Rossby waves modulating thermocline and subsurface heat content variations. Resulting low-frequency changes in the eastern Indian Ocean thermocline depth are associated with decadal variations in the frequency of Indian Ocean dipole (IOD) events, with positive IOD events unusually common in the 1960s and 1990s with a relatively shallow thermocline. In contrast, the deeper thermocline depth in the 1970s and 1980s is associated with frequent negative IOD and rare positive IOD events. Changes in Pacific wind forcing in recent decades and associated rapid increases in Indian Ocean subsurface heat content can thus affect the basin’s leading mode of variability, with implications for regional climate and vulnerable societies in surrounding countries.
    Description: This research was supported by a Research Fellowship by the Alexander von Humboldt Foundation, as well as the Ocean Climate Change Institute and the Investment in Science Fund at WHOI.
    Description: 2017-08-15
    Keywords: Indian Ocean ; Ocean dynamics ; Climate variability ; Multidecadal variability ; Pacific decadal oscillation
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  • 115
    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): 2251-2265, doi:10.1175/JPO-D-17-0042.1.
    Description: The problem of localized dense water formation over a sloping bottom is considered for the general case in which the topography forms a closed contour. This class of problems is motivated by topography around islands or shallow shoals in which convection resulting from brine rejection or surface heat loss reaches the bottom. The focus of this study is on the large-scale circulation that is forced far from the region of surface forcing. The authors find that a cyclonic current is generated around the topography, in the opposite sense to the propagation of the dense water plume. In physical terms, this current results from the propagation of low sea surface height from the region of dense water formation anticyclonically along the topographic contours back to the formation region. This pressure gradient is then balanced by a cyclonic geostrophic flow. This basic structure is well predicted by a linear quasigeostrophic theory, a primitive equation model, and in rotating tank experiments. For sufficiently strong forcing, the anticyclonic circulation of the dense plume meets this cyclonic circulation to produce a sharp front and offshore advection of dense water at the bottom and buoyant water at the surface. This nonlinear limit is demonstrated in both the primitive equation model and in the tank experiments.
    Description: MAS was supported by the National Science Foundation under Grant OCE-1534618. Support for CC was given by the WHOI Ocean Climate Change Institute Proposal 27071273.
    Description: 2018-03-20
    Keywords: Bottom currents ; Buoyancy ; Ocean dynamics ; Density currents
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  • 116
    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 Bulletin of the American Meteorological Society 99, Suppl. S (2018): S21-S26, doi:10.1175/BAMS-D-17-0128.1.
    Description: NOAA Coral Reef Conservation Program; National Science Foundation OCE 1537338, OCE 1605365, OCE 1031971
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  • 117
    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): 1555-1566, doi:10.1175/JPO-D-17-0231.1.
    Description: A primary challenge in modeling flow over shallow coral reefs is accurately characterizing the bottom drag. Previous studies over continental shelves and sandy beaches suggest surface gravity waves should enhance the drag on the circulation over coral reefs. The influence of surface gravity waves on drag over four platform reefs in the Red Sea is examined using observations from 6-month deployments of current and pressure sensors burst sampling at 1Hz for 4–5min. Depth-average current fluctuations U0 within each burst are dominated by wave orbital velocities uw that account for 80%–90%of the burst variance and have a magnitude of order 10 cm s21, similar to the lower-frequency depth-average current Uavg. Previous studies have shown that the cross-reef bottom stress balances the pressure gradient over these reefs. A bottom stress estimate that neglects the waves (rCdaUavgjUavgj, where r is water density and Cda is a drag coefficient) balances the observed pressure gradient when uw is smaller than Uavg but underestimates the pressure gradient when uw is larger than Uavg (by a factor of 3–5 when uw 5 2Uavg), indicating the neglected waves enhance the bottom stress. In contrast, a bottom stress estimate that includes the waves [rCda(Uavg 1 U0)jUavg 1 U0j)] balances the observed pressure gradient independent of the relative size of uw and Uavg, indicating that this estimate accounts for the wave enhancement of the bottom stress. A parameterization proposed by Wright and Thompson provides a reasonable estimate of the total bottom stress (including the waves) given the burst-averaged current and the wave orbital velocity.
    Description: The Red Sea field program was supported by Awards USA 00002 and KSA 00011 made by KAUST. S. Lentz was supported for the analysis by NSF Award OCE-1558343.
    Description: 2019-01-13
    Keywords: Coastal flows ; Currents ; Dynamics ; Gravity waves ; Turbulence
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  • 118
    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 Bulletin of the American Meteorological Society 99 (2018): 513-520, doi:10.1175/BAMS-D-16-0323.1.
    Description: Seasonally ice-covered marginal seas are among the most difficult regions in the Arctic to study. Physical constraints imposed by the variable presence of sea ice in all stages of growth and melt make the upper water column and air–sea ice interface especially challenging to observe. At the same time, the flow of solar energy through Alaska’s marginal seas is one of the most important regulators of their weather and climate, sea ice cover, and ecosystems. The deficiency of observing systems in these areas hampers forecast services in the region and is a major contributor to large uncertainties in modeling and related climate projections. The Arctic Heat Open Science Experiment strives to fill this observation gap with an array of innovative autonomous floats and other near-real-time weather and ocean sensing systems. These capabilities allow continuous monitoring of the seasonally evolving state of the Chukchi Sea, including its heat content. Data collected by this project are distributed in near–real time on project websites and on the Global Telecommunications System (GTS), with the objectives of (i) providing timely delivery of observations for use in weather and sea ice forecasts, for model, and for reanalysis applications and (ii) supporting ongoing research activities across disciplines. This research supports improved forecast services that protect and enhance the safety and economic viability of maritime and coastal community activities in Alaska. Data are free and open to all (see www.pmel.noaa.gov/arctic-heat/).
    Description: This work was supported by NOAA Ocean and Atmospheric Research and the Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA15OAR4320063 and by the Innovative Technology for Arctic Exploration (ITAE) program at JISAO/PMEL. Jayne, Robbins, and Ekholm were supported by ONR (N00014-12-10110).
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  • 119
    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): 893-910, doi:10.1175/JTECH-D-17-0102.1.
    Description: Rotary sidescan sonars are widely used to image the seabed given their high temporal and spatial resolution. This high resolution is necessary to resolve bedform dynamics and evolution; however, sidescan sonars do not directly measure bathymetry, limiting their utility. When sidescan sonars are mounted close to the seabed, bedforms may create acoustical “shadows” that render previous methods that invert the backscatter intensity to estimate bathymetry and are based on the assumption of a fully insonified seabed ineffective. This is especially true in coastal regions, where bedforms are common features whose large height relative to the water depth may significantly influence the surrounding flow. A method is described that utilizes sonar shadows to estimate bedform height and asymmetry. The method accounts for the periodic structure of bedform fields and the projection of the shadows onto adjacent bedforms. It is validated with bathymetric observations of wave-orbital ripples, with wavelengths ranging from 0.3 to 0.8 m, and tidally reversing megaripples, with wavelengths from 5 to 8 m. In both cases, bathymetric-measuring sonars were deployed in addition to a rotary sidescan sonar to provide a ground truth; however, the bathymetric sonars typically measure different and smaller areas than the rotary sidescan sonar. The shadow-based method and bathymetric-measuring sonar data produce estimates of bedform height that agree by 34.0% ± 27.2% for wave-orbital ripples and 16.6% ± 14.7% for megaripples. Errors for estimates of asymmetry are 1.9% ± 2.1% for wave-orbital ripples and 11.2% ± 9.6% for megaripples.
    Description: This project is partially supported by the National Science Foundation through a Graduate Research Fellowship and a Massachusetts Institute of Technology Energy Initiative Fellowship. Additionally, funding used in developing the method was obtained from NSF Grants OCE-1634481 and OCE-1635151. Field work was funded under ONR Grants N00014-06-10329 and N00014-13-1-0364.
    Keywords: Ocean ; Acoustic measurements/effects ; Algorithms ; In situ oceanic observations ; Instrumentation/sensors
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  • 120
    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 he balance of salinity variance in a partially stratified estuary: Implications for exchange flow, mixing, and stratification. Journal of Physical Oceanography, 48(12), (2018) 2887-2899., doi: 10.1175/JPO-D-18-0032.1.
    Description: Salinity variance dissipation is related to exchange flow through the salinity variance balance equation, and meanwhile its magnitude is also proportional to the turbulence production and stratification inside the estuary. As river flow increases, estuarine volume-integrated salinity variance dissipation increases owing to more variance input from the open boundaries driven by exchange flow and river flow. This corresponds to the increased efficient conversion of turbulence production to salinity variance dissipation due to the intensified stratification with higher river flow. Through the spring–neap cycle, the temporal variation of salinity variance dissipation is more dependent on stratification than turbulence production, so it reaches its maximum during the transition from neap to spring tides. During most of the transition time from spring to neap tides, the advective input of salinity variance from the open boundaries is larger than dissipation, resulting in the net increase of variance, which is mainly expressed as vertical variance, that is, stratification. The intensified stratification in turn increases salinity variance dissipation. During neap tides, a large amount of enhanced salinity variance dissipation is induced by the internal shear stress near the halocline. During most of the transition time from neap to spring tides, dissipation becomes larger than the advective input, so salinity variance decreases and the stratification is destroyed.
    Description: TW was supported by the National Key R&D Program of China (Grant 2017YFA0604104), National Natural Science Foundation of China (Grant 41706002), Natural Science Foundation of Jiangsu Province (Grant BK20170864), and MEL Visiting Fellowship (MELRS1617). WRG was supported by NSF Grant OCE 1736539. Part of this work is finished during TW’s visit in MEL and WHOI. We would like to acknowledge John Warner for providing the codes of the Hudson estuary model, and Parker MacCready, the editor, and two reviewers for their insightful suggestions on improving the manuscript.
    Description: 2019-06-06
    Keywords: Estuaries ; Dynamics ; Mixing ; Density Currents
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  • 121
    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): 2127-2140, doi:10.1175/JPO-D-18-0035.1.
    Description: Shipboard hydrographic and velocity measurements collected in summer 2014 are used to study the evolution of the freshwater coastal current in southern Greenland as it encounters Cape Farewell. The velocity structure reveals that the coastal current maintains its identity as it flows around the cape and bifurcates such that most of the flow is diverted to the outer west Greenland shelf, while a small portion remains on the inner shelf. Taking into account this inner branch, the volume transport of the coastal current is conserved, but the freshwater transport decreases on the west side of Cape Farewell. A significant amount of freshwater appears to be transported off the shelf where the outer branch flows adjacent to the shelfbreak circulation. It is argued that the offshore transposition of the coastal current is caused by the flow following the isobaths as they bend offshore because of the widening of the shelf on the west side of Cape Farewell. An analysis of the potential vorticity shows that the subsequent seaward flux of freshwater can be enhanced by instabilities of the current. This set of circumstances provides a pathway for the freshest water originating from the Arctic, as well as runoff from the Greenland ice sheet, to be fluxed into the interior Labrador Sea where it could influence convection in the basin.
    Description: Funding for this project was provided by the National Science Foundation under Grant OCE-1259618.
    Description: 2019-03-11
    Keywords: Boundary currents ; Coastal flows ; Instability ; Ocean circulation ; Potential vorticity ; Transport
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  • 122
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. 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 27 (2010): 210-225, doi:10.1175/2009JTECHO681.1.
    Description: Acoustic Doppler current profilers (ADCPs) are widely used for routine measurements of ocean currents and waves in coastal environments. These instruments have the basic capability to measure surface wave frequency–directional spectra, but the quality of the estimates is not well understood because of the relatively high noise levels in the velocity measurements. In this study, wave data are evaluated from two 600-kHz ADCP instruments deployed at 20- and 45-m depths on the Southern California continental shelf. A simple parametric estimation technique is presented that provides robust estimates of the gross directional wave properties, even when the data quality is marginal, as was often the case in this benign wave environment. Good agreement of mean direction and (to a lesser degree) directional spreading estimates with measurements from a nearby surface-following buoy confirms that reliable wave information can generally be extracted from ADCP measurements on the continental shelf, supporting the instrument’s suitability for routine wave-monitoring applications.
    Description: This research was supported by the National Science Foundation (Physical Oceanography Program) and the Office of Naval Research (Coastal Geosciences Program).
    Keywords: Instrumentation/sensors ; Buoy observations ; Coastal meteorology ; Wave properties
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  • 123
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. 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 40 (2010): 1910–1914, doi:10.1175/2010JPO4483.1.
    Description: Corrigendum: Spall, M. A., R. S. Pickart, P. S. Fratantoni, and A. J. Plueddemann, 2008: Western Arctic shelfbreak eddies: Formation and transport. J. Phys. Oceanogr., 38, 1644–1668
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  • 124
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. 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 40 (2010): 1087-1105, doi:10.1175/2010JPO4312.1.
    Description: Hood Canal, a long fjord in Washington State, has strong tides but limited deep-water renewal landward of a complex constriction. Tide-resolving hydrographic and velocity observations at the constriction, with a depth-cycling towed body, varied markedly during three consecutive years, partly because of stratification variations. To determine whether hydraulic control is generally important and to interpret observations of lee waves, blocking, and other features, hydraulic criticality is estimated over full tidal cycles for channel wide internal wave modes 1, 2, and 3, at five cross-channel sections, using mode speeds from the extended Taylor–Goldstein equation. These modes were strongly supercritical during most of ebb and flood on the gentle seaward sill face and for part of flood at the base of the steep landward side. Examining local criticality along the thalweg found repeated changes between mode 1 being critical and supercritical approaching the sill crest during flood, unsurprising given local minima and maxima in the cross-sectional area, with the sill crest near a maximum. Density crossing the sill sometimes resembled an overflow with an internal hydraulic control at the sill, followed by a hydraulic jump or lee wave. Long-wave speeds, however, suggest cross waves, particularly along the shallower gentler side, where flow downstream of a large-amplitude wave was uniformly supercritical. Supercritical approaching the sill, peak ebb was critical to mode 1 and supercritical to modes 2 and 3 at the base while forming a sluggish dome of dense water over the sill. Full interpretation exceeds observations and existing theory.
    Description: Washington State Sea Grant funded collection of these observations and the Office of Naval Research their publication. Pratt’s efforts were supported by the National Science Foundation under Grant OCE-0525729.
    Keywords: Channel flows ; Field experiments ; Ship observations ; Tides
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  • 125
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 22 (2009): 5175–5204, doi:10.1175/2009JCLI2863.1.
    Description: The Massachusetts Institute of Technology (MIT) Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model’s first projections were published in 2003, substantial improvements have been made to the model, and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections; for example, the median surface warming in 2091–2100 is 5.1°C compared to 2.4°C in the earlier study. Many changes contribute to the stronger warming; among the more important ones are taking into account the cooling in the second half of the twentieth century due to volcanic eruptions for input parameter estimation and a more sophisticated method for projecting gross domestic product (GDP) growth, which eliminated many low-emission scenarios. However, if recently published data, suggesting stronger twentieth-century ocean warming, are used to determine the input climate parameters, the median projected warming at the end of the twenty-first century is only 4.1°C. Nevertheless, all ensembles of the simulations discussed here produce a much smaller probability of warming less than 2.4°C than implied by the lower bound of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) projected likely range for the A1FI scenario, which has forcing very similar to the median projection in this study. The probability distribution for the surface warming produced by this analysis is more symmetric than the distribution assumed by the IPCC because of a different feedback between the climate and the carbon cycle, resulting from the inclusion in this model of the carbon–nitrogen interaction in the terrestrial ecosystem.
    Description: This work was supported in part by the Office of Science (BER), U.S. Department of Energy Grants DE-FG02-94ER61937 and DE-FG02-93ER61677, and by the industrial and foundations sponsors of The MIT Joint Program on the Science and Policy of Global Change (http://globalchange.mit.edu/sponsors/ current.html).
    Keywords: Probability forecasts/models ; Climate prediction ; Anthropogenic effects ; Numerical analysis/modeling ; Feedback
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  • 126
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 39 (2009): 2779-2799, doi:10.1175/2009JPO4075.1.
    Description: The hydraulic state of the exchange circulation through the Strait of Gibraltar is defined using a recently developed critical condition that accounts for cross-channel variations in layer thickness and velocity, applied to the output of a high-resolution three-dimensional numerical model simulating the tidal exchange. The numerical model uses a coastal-following curvilinear orthogonal grid, which includes, in addition to the Strait of Gibraltar, the Gulf of Cadiz and the Alboran Sea. The model is forced at the open boundaries through the specification of the surface tidal elevation that is characterized by the two principal semidiurnal and two diurnal harmonics: M2, S2, O1, and K1. The simulation covers an entire tropical month. The hydraulic analysis is carried out approximating the continuous vertical stratification first as a two-layer system and then as a three-layer system. In the latter, the transition zone, generated by entrainment and mixing between the Atlantic and Mediterranean flows, is considered as an active layer in the hydraulic model. As result of these vertical approximations, two different hydraulic states have been found; however, the simulated behavior of the flow only supports the hydraulic state predicted by the three-layer case. Thus, analyzing the results obtained by means of the three-layer hydraulic model, the authors have found that the flow in the strait reaches maximal exchange about 76% of the tropical monthlong period.
    Keywords: Channel flows ; Seas/gulfs/bays ; Mediterranean Sea ; Tides ; Orographic effects
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  • 127
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 39 (2009): 1077–1096, doi:10.1175/2008JPO4044.1.
    Description: Observations of turbulent kinetic energy (TKE) dynamics in the ocean surface boundary layer are presented here and compared with results from previous observational, numerical, and analytic studies. As in previous studies, the dissipation rate of TKE is found to be higher in the wavy ocean surface boundary layer than it would be in a flow past a rigid boundary with similar stress and buoyancy forcing. Estimates of the terms in the turbulent kinetic energy equation indicate that, unlike in a flow past a rigid boundary, the dissipation rates cannot be balanced by local production terms, suggesting that the transport of TKE is important in the ocean surface boundary layer. A simple analytic model containing parameterizations of production, dissipation, and transport reproduces key features of the vertical profile of TKE, including enhancement near the surface. The effective turbulent diffusion coefficient for heat is larger than would be expected in a rigid-boundary boundary layer. This diffusion coefficient is predicted reasonably well by a model that contains the effects of shear production, buoyancy forcing, and transport of TKE (thought to be related to wave breaking). Neglect of buoyancy forcing or wave breaking in the parameterization results in poor predictions of turbulent diffusivity. Langmuir turbulence was detected concurrently with a fraction of the turbulence quantities reported here, but these times did not stand out as having significant differences from observations when Langmuir turbulence was not detected.
    Description: The Office of Naval Research funded this work as a part of CBLAST-Low.
    Keywords: Turbulence ; Boundary layer ; Sea/ocean surface ; Air-sea interaction ; Energy transport
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  • 128
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    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 39 (2009): 1060-1068, doi:10.1175/2008JPO3996.1.
    Description: The response of a weakly stratified layer of fluid to a surface cooling distribution is investigated with linear theory in an attempt to clarify recent numerical results concerning the sinking of cooled water in polar ocean boundary currents. A channel of fluid is forced at the surface by a cooling distribution that varies in the down-channel as well as the cross-channel directions. The resulting geostrophic flow in the central region of the channel impinges on its boundaries, and regions of strong downwelling are observed. For the parameters of the problem investigated, the downwelling occurs in a classical Stewartson layer but the forcing of the layer leads to an unusual relation with the interior flow, which is forced to satisfy the thermal condition on the boundary while the geostrophic normal flow in the interior is brought to rest in the boundary layer. As a consequence of the layer’s dynamics, the resulting long-channel flow exhibits a nonmonotonic approach to the interior flow, and the strongest vertical velocities are limited to the boundary layer whose scale is so small that numerical models resolve the region only with great difficulty. The analytical model presented here is able to reproduce key features of the previous nonlinear numerical calculations.
    Description: This research was supported in part by NSF Grant OCE 0451086.
    Keywords: Forcing ; Boundary currents ; Upwelling, downwelling
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  • 129
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 39 (2009): 107-124, doi:10.1175/2008JPO3952.1.
    Description: In most estuarine systems it is assumed that the dominant along-channel momentum balance is between the integrated pressure gradient and bed stress. Scaling the amplitude of the estuarine circulation based on this balance has been shown to have predictive skill. However, a number of authors recently highlighted important nonlinear processes that contribute to the subtidal dynamics at leading order. In this study, a previously validated numerical model of the Hudson River estuary is used to examine the forces driving the residual estuarine circulation and to test the predictive skill of two linear scaling relationships. Results demonstrate that the nonlinear advective acceleration terms contribute to the subtidal along-channel momentum balance at leading order. The contribution of these nonlinear terms is driven largely by secondary lateral flows. Under a range of forcing conditions in the model runs, the advective acceleration terms nearly always act in concert with the baroclinic pressure gradient, reinforcing the residual circulation. Despite the strong contribution of the nonlinear advective terms to the subtidal dynamical balance, a linear scaling accurately predicts the strength of the observed residual circulation in the model. However, this result is largely fortuitous, as this scaling does not account for two processes that are fundamental to the estuarine circulation. The skill of this scaling results because of the compensatory relationship between the contribution of the advective acceleration terms and the suppression of turbulence due to density stratification. Both of these processes, neither of which is accounted for in the linear scaling, increase the residual estuarine circulation but have an opposite dependence on tidal amplitude and, consequently, strength of stratification.
    Description: This research was supported by the Beacon Institute for Rivers and Estuaries—Woods Hole Oceanographic Institution postdoctoral fellowship program, as well as NSF Grants OCE-0452054 and OCE-0451740.
    Keywords: Advection ; Estuarine circulation ; Friction ; Density currents ; Baroclinic flows
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  • 130
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 39 (2009): 1258-1271, doi:10.1175/2008JPO4028.1.
    Description: This paper presents a set of laboratory experiments focused on how a buoyant coastal current flowing over a sloping bottom interacts with a canyon and what controls the separation, if any, of the current from the upstream canyon bend. The results show that the separation of a buoyant coastal current depends on the current width W relative to the radius of curvature of the bathymetry ρc. The flow moved across the mouth of the canyon (i.e., separated) for W/ρc 〉 1, in agreement with previous results. The present study extends previous work by examining both slope-controlled and surface-trapped currents, and using a geometry specific to investigating buoyant current–canyon interaction. The authors find that, although bottom friction is important in setting the position of the buoyant front, the separation process driven by the inertia of the flow could overcome even the strongest bathymetric influence. Application of the laboratory results to the East Greenland Current (EGC), an Arctic-origin buoyant current that is observed to flow in two branches south of Denmark Strait, suggests that the path of the EGC is influenced by the large canyons cutting across the shelf, as the range of W/ρc in the ocean spans those observed in the laboratory. What causes the formation of a two-branched EGC structure downstream of the Kangerdlugssuaq Canyon (68°N, 32°W) is still unclear, but potential mechanisms are discussed.
    Description: This work was partially funded by NSF Grant OCE-0450658. DS also received support from the Academic Programs Office of the Woods Hole Oceanographic Institution, while CC had partial support from NSF OCE-0350891.
    Keywords: Coastal flows ; Buoyancy ; Currents ; Experimental design ; Topographic effects
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  • 131
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 39 (2009): 915-933, doi:10.1175/2008JPO3933.1.
    Description: The temporal response of the length of a partially mixed estuary to changes in freshwater discharge Qf and tidal amplitude UT is studied using a 108-day time series collected along the length of the Hudson River estuary in the spring and summer of 2004 and a long-term (13.4 yr) record of Qf, UT, and near-surface salinity. When Qf was moderately high, the tidally averaged length of the estuary L5, here defined as the distance from the mouth to the up-estuary location where the vertically averaged salinity is 5 psu, fluctuated by more than 47 km over the spring–neap cycle, ranging from 28 to 〉75 km. During low flow periods, L5 varied very little over the spring–neap cycle and approached a steady length. The response is quantified and compared to predictions of a linearized model derived from the global estuarine salt balance. The model is forced by fluctuations in Qf and UT relative to average discharge Qo and tidal amplitude UTo and predicts the linear response time scale τ and the steady-state length Lo for average forcing. Two vertical mixing schemes are considered, in which 1) mixing is proportional to UT and 2) dependence of mixing on stratification is also parameterized. Based on least squares fits between L5 and estuary length predicted by the model, estimated τ varied by an order of magnitude from a period of high average discharge (Qo = 750 m3 s−1, τ = 4.2 days) to a period of low discharge (Qo = 170 m3 s−1, τ = 40.4 days). Over the range of observed discharge, Lo Qo−0.30±0.03, consistent with the theoretical scaling for an estuary whose landward salt flux is driven by vertical estuarine exchange circulation. Estimated τ was proportional to the discharge advection time scale (LoA/Qo, where A is the cross-sectional area of the estuary). However, τ was 3–4 times larger than the theoretical prediction. The model with stratification-dependent mixing predicted variations in L5 with higher skill than the model with mixing proportional to UT. This model provides insight into the time-dependent response of a partially stratified estuary to changes in forcing and explains the strong dependence of the amplitude of the spring–neap response on freshwater discharge. However, the utility of the linear model is limited because it assumes a uniform channel, and because the underlying dynamics are nonlinear, and the forcing Qf and UT can undergo large amplitude variations. River discharge, in particular, can vary by over an order of magnitude over time scales comparable to or shorter than the response time scale of the estuary.
    Description: This study was generously funded by Hudson River Foundation Grant 005/03A and NSF Grant OCE-0452054. Lerczak also received partial support from the Woods Hole Center for Oceans and Human Health, NSF Grant OCE-0430724 and NIEHS Grant 1-P50-ES012742-01.
    Keywords: Estuaries ; Rivers ; Tides ; Stability ; Vertical motion
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  • 132
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. 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 90 (2009): 1337-1350, doi:10.1175/2008BAMS2499.1.
    Description: The Vasco—Cirene program ex-plores how strong air—sea inter-actions promoted by the shallow thermocline and high sea surface temperature in the Seychelles—Chagos thermocline ridge results in marked variability at synoptic, intraseasonal, and interannual time scales. The Cirene oceano-graphic cruise collected oceanic, atmospheric, and air—sea flux observations in this region in Jan-uary—February 2007. The contem-poraneous Vasco field experiment complemented these measure-ments with balloon deployments from the Seychelles. Cirene also contributed to the development of the Indian Ocean observing system via deployment of a moor-ing and 12 Argo profilers. Unusual conditions prevailed in the Indian Ocean during Janu-ary and February 2007, following the Indian Ocean dipole climate anomaly of late 2006. Cirene measurements show that the Seychelles—Chagos thermocline ridge had higher-than-usual heat content with subsurface anomalies up to 7°C. The ocean surface was warmer and fresher than average, and unusual eastward currents prevailed down to 800 m. These anomalous conditions had a major impact on tuna fishing in early 2007. Our dataset also sampled the genesis and maturation of Tropical Cyclone Dora, including high surface temperatures and a strong diurnal cycle before the cyclone, followed by a 1.5°C cool-ing over 10 days. Balloonborne instruments sampled the surface and boundary layer dynamics of Dora. We observed small-scale structures like dry-air layers in the atmosphere and diurnal warm layers in the near-surface ocean. The Cirene data will quantify the impact of these finescale features on the upper-ocean heat budget and atmospheric deep convection.
    Description: CNES funded the Vasco part of the experiment; INSU funded the Cirene part. R/V Suroît is an Ifremer ship. The contributions from ODU, WHOI, and FOI (Sweden) are supported by the National Science Foundation under Grant Number 0525657. The participation of the University of Miami group was funded though NASA (NNG04HZ33C). PMEL participation was supported through NOAA’s Office of Climate Observation.
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  • 133
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 21 (2008): 3776–3796, doi:10.1175/2008JCLI2038.1.
    Description: The impact of carbon–nitrogen dynamics in terrestrial ecosystems on the interaction between the carbon cycle and climate is studied using an earth system model of intermediate complexity, the MIT Integrated Global Systems Model (IGSM). Numerical simulations were carried out with two versions of the IGSM’s Terrestrial Ecosystems Model, one with and one without carbon–nitrogen dynamics. Simulations show that consideration of carbon–nitrogen interactions not only limits the effect of CO2 fertilization but also changes the sign of the feedback between the climate and terrestrial carbon cycle. In the absence of carbon–nitrogen interactions, surface warming significantly reduces carbon sequestration in both vegetation and soil by increasing respiration and decomposition (a positive feedback). If plant carbon uptake, however, is assumed to be nitrogen limited, an increase in decomposition leads to an increase in nitrogen availability stimulating plant growth. The resulting increase in carbon uptake by vegetation exceeds carbon loss from the soil, leading to enhanced carbon sequestration (a negative feedback). Under very strong surface warming, however, terrestrial ecosystems become a carbon source whether or not carbon–nitrogen interactions are considered. Overall, for small or moderate increases in surface temperatures, consideration of carbon–nitrogen interactions result in a larger increase in atmospheric CO2 concentration in the simulations with prescribed carbon emissions. This suggests that models that ignore terrestrial carbon–nitrogen dynamics will underestimate reductions in carbon emissions required to achieve atmospheric CO2 stabilization at a given level. At the same time, compensation between climate-related changes in the terrestrial and oceanic carbon uptakes significantly reduces uncertainty in projected CO2 concentration.
    Keywords: Carbon dioxide ; Chemistry, atmospheric ; Greenhouse gases ; Ecosystem effects ; Temperature
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  • 134
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 104–120, doi:10.1175/2007JPO3686.1.
    Description: Recent studies have indicated that the North Atlantic Ocean subpolar gyre circulation undergoes significant interannual-to-decadal changes in response to variability in atmospheric forcing. There are also observations, however, suggesting that the southern limb of the subpolar gyre, namely, the eastward-flowing North Atlantic Current (NAC), may be quasi-locked to particular latitudes in the central North Atlantic by fracture zones (gaps) in the Mid-Atlantic Ridge. This could constrain the current’s ability to respond to variability in forcing. In the present study, subsurface float trajectories at 100–1000 m collected during 1997–99 and satellite-derived surface geostrophic velocities from 1992 to 2006 are used to provide an improved description of the detailed pathways of the NAC over the ridge and their relationship to bathymetry. Both the float and satellite observations indicate that in 1997–99, the northern branch of the NAC was split into two branches as it crossed the ridge, one quasi-locked to the Charlie–Gibbs Fracture Zone (CGFZ; 52°–53°N) and the other to the Faraday Fracture Zone (50°–51°N). The longer satellite time series shows, however, that this pattern did not persist outside the float sampling period and that other branching modes persisted for one or more years, including an approximately 12-month time period in 2002–03 when the strongest eastward flow over the ridge was at 49°N. Schott et al. showed how northward excursions of the NAC can temporarily block the westward flow of the Iceland–Scotland Overflow Water through the CGFZ. From the 13-yr time series of surface geostrophic velocity, it is estimated that such blocking may occur on average 6% of the time, although estimates for any given 12-month period range from 0% to 35%.
    Description: This research was supported by National Science Foundation Grants OCE-9531877 to the Woods Hole Oceanographic Institution (WHOI) and OCE-9906775 to the University of Rhode Island, by the WHOI Summer Student Fellowship Program, and by the Lawrence J. Pratt and Melinda M. Hall Endowed Fund for Interdisciplinary Research at the Woods Hole Oceanographic Institution.
    Keywords: Currents ; Topographic effects ; Interannual variability ; Forcing ; Gyres
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  • 135
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 880–895, doi:10.1175/2007JPO3750.1.
    Description: The oceanic response to overflows is explored using a two-layer isopycnal model. Overflows enter the open ocean as dense gravity currents that flow along and down the continental slope. While descending the slope, overflows typically double their volume transport by entraining upper oceanic water. The upper oceanic layer must balance this loss of mass, and the resulting convergent flow produces significant vortex stretching. Overflows thus represent an intense and localized mass and vorticity forcing for the upper ocean. In this study, simulations show that the upper ocean responds to the overflow-induced forcing by establishing topographic β plumes that are aligned more or less along isobaths and that have a transport that is typically a few times larger than that of the overflows. For the topographic β plume driven by the Mediterranean overflow, the occurrence of eddies near Cape St. Vincent, Portugal, allows the topographic β plume to flow across isobaths. The modeled topographic β-plume circulation forms two transatlantic zonal jets that are analogous to the Azores Current and the Azores Countercurrent. In other cases (e.g., the Denmark Strait overflow), the same kind of circulation remains trapped along the western boundary and hence would not be readily detected.
    Description: SK’s support during the time of his Ph.D. research in the MIT/WHOI Joint Program was provided by the National Science Foundation through Grant OCE04-24741. JP and JY have also received support from the Climate Process Team on Gravity Current Entrainment, NSF Grant OCE-0611530.
    Keywords: North Atlantic Ocean ; Mediterranean region ; Ocean models ; Mass fluxes/transport ; Diapycnal mixing
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  • 136
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 909–917, doi:10.1175/2007JPO3535.1.
    Description: The classical two-box model of Stommel is extended in two directions: replacing the buoyancy constraint with an energy constraint and including the wind-driven gyre. Stommel postulated a buoyancy constraint for the thermohaline circulation, and his basic idea has evolved into the dominating theory of thermohaline circulation; however, recently, it is argued that the thermohaline circulation is maintained by mechanical energy from wind stress and tides. The major difference between these two types of models is the bifurcation structure: the Stommel-like model has two thermal modes (one stable and another one unstable) and one stable haline mode, whereas the energy-constraint model has one stable thermal mode and two saline modes (one stable and another one unstable). Adding the wind-driven gyre changes the threshold value of thermohaline bifurcation greatly; thus, the inclusion of the wind-driven gyre is a vital step in completely modeling the physical processes related to thermohaline circulation.
    Description: YPG was supported by the National Science Foundation of China (NSFC, 40676022), the National Basic Research Program of China (2006CB403605), and the Guangdong Natural Science Foundation (5003672). RXH was supported by the National Oceanic and Atmospheric Administration through CICOR Cooperative Agreement NA17RJ1223 to the Woods Hole Oceanographic Institution.
    Keywords: Thermohaline circulation ; Mixing ; Wind stress ; Buoyancy ; Energy budget
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  • 137
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 380-399, doi:10.1175/2007JPO3728.1.
    Description: Barotropic to baroclinic conversion and attendant phenomena were recently examined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two distinct mixing processes appear to be at work in the waters above the 1100-m-deep ridge crest. At middepths, above 400 m, mixing events resemble their open-ocean counterparts. There is no apparent modulation of mixing rates with the fortnightly cycle, and they are well modeled by standard open-ocean parameterizations. Nearer to the topography, there is quasi-deterministic breaking associated with each baroclinic crest passage. Large-amplitude, small-scale internal waves are triggered by tidal forcing, consistent with lee-wave formation at the ridge break. These waves have vertical wavelengths on the order of 400 m. During spring tides, the waves are nonlinear and exhibit convective instabilities on their leading edge. Dissipation rates exceed those predicted by the open-ocean parameterizations by up to a factor of 100, with the disparity increasing as the seafloor is approached. These observations are based on a set of repeated CTD and microconductivity profiles obtained from the research platform (R/P) Floating Instrument Platform (FLIP), which was trimoored over the southern edge of the ridge crest. Ocean velocity and shear were resolved to a 4-m vertical scale by a suspended Doppler sonar. Dissipation was estimated both by measuring overturn displacements and from microconductivity wavenumber spectra. The methods agreed in water deeper than 200 m, where sensor resolution limitations do not limit the turbulence estimates. At intense mixing sites new phenomena await discovery, and existing parameterizations cannot be expected to apply.
    Description: This work was funded by the National Science Foundation as a component of the Hawaii Ocean Mixing Program. Added support for FLIP was provided by the Office of Naval Research.
    Keywords: Pacific Ocean ; Topographic effects ; Internal waves ; Barotropic flows ; Baroclinic flows
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  • 138
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 2164–2184, doi:10.1175/2008JPO3962.1.
    Description: This is the second part of a two-part investigation of a coupled wind and wave model that includes the enhanced form drag of breaking waves. The model is based on the wave energy balance and the conservation of air-side momentum and energy. In Part I, coupled nonlinear advance–delay differential equations were derived, which govern the wave height spectrum, the distribution of breaking waves, and vertical air side profiles of the turbulent stress and wind speed. Numeric solutions were determined for mature seas. Here, numeric solutions for a wide range of wind and wave conditions are obtained, including young, strongly forced wind waves. Furthermore, the “spatial sheltering effect” is introduced so that smaller waves in airflow separation regions of breaking longer waves cannot be forced by the wind. The solutions strongly depend on the wave height curvature spectrum at high wavenumbers (the “threshold saturation level”). As the threshold saturation level is reduced, the effect of breaking waves becomes stronger. For young strongly forced waves (laboratory conditions), breaking waves close to the spectral peak dominate the wind input and previous solutions of a model with only input to breaking waves are recovered. Model results of the normalized roughness length are generally consistent with previous laboratory and field measurements. For field conditions, the wind stress depends sensitively on the wave height spectrum. The spatial sheltering may modify the number of breaking shorter waves, in particular, for younger seas.
    Description: This work was supported by the U.S. National Science Foundation (Grant OCE- 0526177) and the U.S. Office of Naval Research (Grant N00014–06–10729).
    Keywords: Wave breaking ; Coupled models ; Wind stress ; Momentum ; Sea state
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  • 139
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 2341-2357, doi:10.1175/2008JPO3986.1.
    Description: Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth. During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1–6 cm s−1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf “Hasselmann wave stress” due to the influence of the earth’s rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.
    Description: This research was funded by the Ocean Sciences Division of the National Science Foundation under Grants OCE-0241292 and OCE-0548961.
    Keywords: Continental shelf ; Transport ; Shear structure/flows ; Coastal flows ; Gravity waves
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  • 140
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 1203–1221, doi:10.1175/2007JPO3768.1.
    Description: Analyses of current time series longer than 200 days from 33 sites over the Middle Atlantic Bight continental shelf reveal a consistent mean circulation pattern. The mean depth-averaged flow is equatorward, alongshelf, and increases with increasing water depth from 3 cm s−1 at the 15-m isobath to 10 cm s−1 at the 100-m isobath. The mean cross-shelf circulation exhibits a consistent cross-shelf and vertical structure. The near-surface flow is typically offshore (positive, range −3 to 6 cm s−1). The interior flow is onshore and remarkably constant (−0.2 to −1.4 cm s−1). The near-bottom flow increases linearly with increasing water depth from −1 cm s−1 (onshore) in shallow water to 4 cm s−1 (offshore) at the 250-m isobath over the slope, with the direction reversal near the 50-m isobath. A steady, two-dimensional model (no along-isobath variations in the flow) reproduces the main features of the observed circulation pattern. The depth-averaged alongshelf flow is primarily driven by an alongshelf pressure gradient (sea surface slope of 3.7 × 10−8 increasing to the north) and an opposing mean wind stress that also drives the near-surface offshore flow. The alongshelf pressure gradient accounts for both the increase in the alongshelf flow with water depth and the geostrophic balance onshore flow in the interior. The increase in the near-bottom offshore flow with water depth is due to the change in the relative magnitude of the contributions from the geostrophic onshore flow that dominates in shallow water and the offshore flow driven by the bottom stress that dominates in deeper water.
    Description: This research was funded by Ocean Sciences Division of the National Science Foundation under Grants OCE-820773, OCE-841292, and OCE-848961.
    Keywords: Ocean models ; Ocean circulation ; Continental shelf ; Currents ; In situ observations
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  • 141
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 133–145, doi:10.1175/2007JPO3782.1.
    Description: Five ice-tethered profilers (ITPs), deployed between 2004 and 2006, have provided detailed potential temperature θ and salinity S profiles from 21 anticyclonic eddy encounters in the central Canada Basin of the Arctic Ocean. The 12–35-m-thick eddies have center depths between 42 and 69 m in the Arctic halocline, and are shallower and less dense than the majority of eddies observed previously in the central Canada Basin. They are characterized by anomalously cold θ and low stratification, and have horizontal scales on the order of, or less than, the Rossby radius of deformation (about 10 km). Maximum azimuthal speeds estimated from dynamic heights (assuming cyclogeostrophic balance) are between 9 and 26 cm s−1, an order of magnitude larger than typical ambient flow speeds in the central basin. Eddy θ–S and potential vorticity properties, as well as horizontal and vertical scales, are consistent with their formation by instability of a surface front at about 80°N that appears in historical CTD and expendable CTD (XCTD) measurements. This would suggest eddy lifetimes longer than 6 months. While the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism, it is less likely since deeper eddies that would originate from the deeper-reaching boundary flows are not observed in the survey region.
    Description: The engineering design work for the ITP was initiated by the Cecil H. and Ida M. Green Technology Innovation Program (an internal program at the Woods Hole Oceanographic Institution). Prototype development and construction were funded jointly by the U.S. National Science Foundation (NSF) Oceanographic Technology and Interdisciplinary Coordination Program and Office of Polar Programs (OPP) under Award OCE-0324233. Continued support has been provided by the OPP Arctic Sciences Section under Award ARC-0519899 and internal WHOI funding.
    Keywords: Arctic ; Eddies ; Profilers ; Stability ; Salinity
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  • 142
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    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 686-701, doi:10.1175/2007JPO3826.1.
    Description: The disintegration of a first-mode internal tide into shorter solitary-like waves is considered. Since observations frequently show both tides and waves with amplitudes beyond the restrictions of weakly nonlinear theory, the evolution is studied using a fully nonlinear, weakly nonhydrostatic two-layer theory that includes rotation. In the hydrostatic limit, the governing equations have periodic, nonlinear inertia–gravity solutions that are explored as models of the nonlinear internal tide. These long waves are shown to be robust to weak nonhydrostatic effects. Numerical solutions show that the disintegration of an initial sinusoidal linear internal tide is closely linked to the presence of these nonlinear waves. The initial tide steepens due to nonlinearity and sheds energy into short solitary waves. The disintegration is halted as the longwave part of the solution settles onto a state close to one of the nonlinear hydrostatic solutions, with the short solitary waves superimposed. The degree of disintegration is a function of initial amplitude of the tide and the properties of the underlying nonlinear hydrostatic solutions, which, depending on stratification and tidal frequency, exist only for a finite range of amplitudes (or energies). There is a lower threshold below which no short solitary waves are produced. However, for initial amplitudes above another threshold, given approximately by the energy of the limiting nonlinear hydrostatic inertia–gravity wave, most of the initial tidal energy goes into solitary waves. Recent observations in the South China Sea are briefly discussed.
    Description: KRH was supported by a Woods Hole Oceanographic Institution Mellon Independent Study Award and ONR Grant N000140610798.
    Keywords: Tides ; Internal waves ; Solitary waves ; Inertia–gravity waves ; Rotation
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  • 143
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 1644-1668, doi:10.1175/2007JPO3829.1.
    Description: The mean structure and time-dependent behavior of the shelfbreak jet along the southern Beaufort Sea, and its ability to transport properties into the basin interior via eddies are explored using high-resolution mooring data and an idealized numerical model. The analysis focuses on springtime, when weakly stratified winter-transformed Pacific water is being advected out of the Chukchi Sea. When winds are weak, the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of O(25 cm s−1) and an eastward transport of 0.42 Sv (1 Sv ≡ 106 m3 s−1). Despite the absence of winds, the current is highly time dependent, with relative vorticity and twisting vorticity often important components of the Ertel potential vorticity. An idealized primitive equation model forced by dense, weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site. The model boundary current is also highly variable, and produces numerous strong, small anticyclonic eddies that transport the shelf water into the basin interior. Analysis of the energy conversion terms in both the mooring data and the numerical model indicates that the eddies are formed via baroclinic instability of the boundary current. The structure of the eddies in the basin interior compares well with observations from drifting ice platforms. The results suggest that eddies shed from the shelfbreak jet contribute significantly to the offshore flux of heat, salt, and other properties, and are likely important for the ventilation of the halocline in the western Arctic Ocean. Interaction with an anticyclonic basin-scale circulation, meant to represent the Beaufort gyre, enhances the offshore transport of shelf water and results in a loss of mass transport from the shelfbreak jet.
    Description: This study was supported by the National Science Foundation Office of Polar Programs under Grants 0421904 and 035268 (MS), and by the Office of Naval Research Grant N00014-02-1-0317 (RP and PF). Analysis by AJP was supported by the Office of Naval Research under Grant N00014-97-1-0135 and by the National Science Foundation under Grant OPP-9815303.
    Keywords: Arctic ; Eddies ; Transport ; Currents ; Jets
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  • 144
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 1992-2002, doi:10.1175/2008JPO3669.1.
    Description: This paper extends A. Bracco and J. Pedlosky’s investigation of the eddy-formation mechanism in the eastern Labrador Sea by including a more realistic depiction of the boundary current. The quasigeostrophic model consists of a meridional, coastally trapped current with three vertical layers. The current configuration and topographic domain are chosen to match, as closely as possible, the observations of the boundary current and the varying topographic slope along the West Greenland coast. The role played by the bottom-intensified component of the boundary current on the formation of the Labrador Sea Irminger Rings is explored. Consistent with the earlier study, a short, localized bottom-trapped wave is responsible for most of the perturbation energy growth. However, for the instability to occur in the three-layer model, the deepest component of the boundary current must be sufficiently strong, highlighting the importance of the near-bottom flow. The model is able to reproduce important features of the observed vortices in the eastern Labrador Sea, including the polarity, radius, rate of formation, and vertical structure. At the time of formation, the eddies have a surface signature as well as a strong circulation at depth, possibly allowing for the transport of both surface and near-bottom water from the boundary current into the interior basin. This work also supports the idea that changes in the current structure could be responsible for the observed interannual variability in the number of Irminger Rings formed.
    Description: AB is supported by WHOI unrestricted funds, JP by the National Science Foundation OCE 85108600, and RP by 0450658.
    Keywords: Eddies ; Boundary currents ; Quasigeostrophic models ; North Atlantic ; Coastlines
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  • 145
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2008. 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 38 (2008): 2294-2307, doi:10.1175/2008JPO3853.1.
    Description: A linear stability analysis of a meridional boundary current on the beta plane is presented. The boundary current is idealized as a constant-speed meridional jet adjacent to a semi-infinite motionless far field. The far-field region can be situated either on the eastern or the western side of the jet, representing a western or an eastern boundary current, respectively. It is found that when unstable, the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field. This is the so-called radiating instability and is found in both barotropic and two-layer baroclinic configurations. A second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents. An eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers. It generates waves with amplitude envelopes that decay slowly with distance from the current. The radiating waves tend to have an asymmetrical horizontal structure—they are much longer in the zonal direction than in the meridional, a consequence of which is that unstable eastern boundary currents, unlike western boundary currents, have the potential to act as a source of zonal jets for the interior of the ocean.
    Description: This work was supported by the National Science Foundation through Grants OCE- 0423975 (MS, HH) and OCE-9901654 (JP). HH would like to thank her thesis committee as well as the MIT– WHOI Joint Program for partial financial support.
    Keywords: Instability ; Boundary currents
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  • 146
    Publication Date: 2022-05-25
    Description: Author Posting. ©American Meteorological Society, 2008. 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 89 (2008): 1307-1324, doi:10.1175/2008BAMS2508.1.
    Description: Greenland has a major influence on the atmospheric circulation of the North Atlantic–western European region, dictating the location and strength of mesoscale weather systems around the coastal seas of Greenland and directly influencing synoptic-scale weather systems both locally and downstream over Europe. High winds associated with the local weather systems can induce large air–sea fluxes of heat, moisture, and momentum in a region that is critical to the overturning of the thermohaline circulation, and thus play a key role in controlling the coupled atmosphere–ocean climate system. The Greenland Flow Distortion Experiment (GFDex) is investigating the role of Greenland in defining the structure and predictability of both local and downstream weather systems through a program of aircraft-based observation and numerical modeling. The GFDex observational program is centered upon an aircraft-based field campaign in February and March 2007, at the dawn of the International Polar Year. Twelve missions were flown with the Facility for Airborne Atmospheric Measurements' BAe-146, based out of the Keflavik, Iceland. These included the first aircraft-based observations of a reverse tip jet event, the first aircraft-based observations of barrier winds off of southeast Greenland, two polar mesoscale cyclones, a dramatic case of lee cyclogenesis, and several targeted observation missions into areas where additional observations were predicted to improve forecasts. In this overview of GFDex the background, aims and objectives, and facilities and logistics are described. A summary of the campaign is provided, along with some of the highlights of the experiment.
    Description: The GFDex would not have been possible without the dedication and flexibility shown by all at the FAAM, DirectFlight, and Avalon. GFDex was funded by the Natural Environmental Research Council (NE/C003365/1), the Canadian Foundation for Climate and Atmospheric Sciences (GR-641), and the European Union Fleet for Airborne Research (EUFAR) and European Union Coordinated Observing System (EUCOS) schemes.
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  • 147
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 20 (2007): 5707–5714, doi:10.1175/2007JCLI1779.1.
    Description: The interannual variation in cold-air outbreak activity over the Japan Sea is investigated using Japan Meteorological Agency buoy 21002 and Quick Scatterometer (QuikSCAT) wind data, Japan Oceanographic Data Center sea surface temperature (SST) data, NCEP–NCAR reanalysis surface wind and sea level pressure (SLP) data, and the winter Arctic Oscillation (AO) index of Thompson and Wallace. Cold-air outbreaks occur during the “winter” November–March period, and wind data for this season for the 19-winter period 1981–2000 were analyzed. Wavelet spectra averaged between 5- and 15-day periods were used to evaluate the intensity of cold-air outbreaks quantitatively. The winter mean wavelet spectra exhibited a clear interannual variation and a significant positive correlation with the AO index, indicating that intensive cold-air outbreaks frequently occur during relatively warm winters caused by a quasi-decadal AO. Based on the SST and SLP data, the low atmospheric surface pressure disturbances tend to develop over the warm East China Sea in warm winters in the positive AO phase. As these low SLP disturbances advance toward the northern Japan islands during the positive AO phase, they intensify more, leading to stronger cold-air outbreaks over the Japan Sea and increased sea surface cooling over the northern Japan Sea.
    Keywords: Air-sea interactions ; Interannual variation ; Arctic Oscillation ; Remote sensing ; Buoy observations
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  • 148
    facet.materialart.
    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 2776-2784, doi:10.1175/2007JPO3710.1.
    Description: The bottom boundary layer of a stratified flow on a coastal continental shelf is examined using the model of Chapman and Lentz. The flow is driven by a surface stress, uniform in the alongshore coordinate, in a downwelling-favorable direction. The stress diminishes in the offshore direction and produces an Ekman pumping, as well as an onshore Ekman flux. The model yields an interior flow, sandwiched between an upper Ekman layer and a bottom boundary layer. The interior has a horizontal density gradient produced by a balance between horizontal diffusion of density and vertical advection of a background vertical density gradient. The interior flow is vertically sheared and in thermal wind balance. Whereas the original model of Chapman and Lentz considered an alongshore flow that is freely evolving, the present note focuses on the equilibrium structure of a flow driven by stress and discusses the vertical and lateral structure of the flow and, in particular, the boundary layer thickness. The vertical diffusivity of density in the bottom boundary layer is considered so strong, locally, as to render the bottom boundary layer’s density a function of only offshore position. Boundary layer budgets of mass, momentum, and buoyancy determine the barotropic component of the interior flow as well as the boundary layer thickness, which is a function of the offshore coordinate. The alongshore flow has enhanced vertical shear in the boundary layer that reduces the alongshore flow in the boundary layer; however, the velocity at the bottom is generally not zero but produces a stress that locally balances the applied surface stress. The offshore transport in the bottom boundary layer therefore balances the onshore surface Ekman flux. The model predicts the thickness of the bottom boundary layer, which is a complicated function of several parameters, including the strength of the forcing stress, the vertical and horizontal diffusion coefficients in the interior, and the horizontal diffusion in the boundary layer. The model yields a boundary layer over only a finite portion of the bottom slope if the interior diffusion coefficients are too large; otherwise, the layer extends over the full lateral extent of the domain.
    Description: This research was supported in part by NSF Grant OCE-851086.00.
    Keywords: Boundary layer ; Continental shelf ; Coastal flows ; Ekman pumping ; Forcing
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  • 149
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 88 (2007): 311-317, doi:10.1175/bams-88-3-311.
    Description: The record-setting 2005 hurricane season has highlighted the urgent need for a better understanding of the factors that contribute to hurricane intensity, and for the development of corresponding advanced hurricane prediction models to improve intensity forecasts. The lack of skill in present forecasts of hurricane intensity may be attributed, in part, to deficiencies in the current prediction models—insufficient grid resolution, inadequate surface and boundary-layer formulations, and the lack of full coupling to a dynamic ocean. The extreme high winds, intense rainfall, large ocean waves, and copious sea spray in hurricanes push the surface-exchange parameters for temperature, water vapor, and momentum into untested regimes. The Coupled Boundary Layer Air–Sea Transfer (CBLAST)-Hurricane program is aimed at developing improved parameterizations using observations from the CBLAST-Hurricane field program that will be suitable for the next generation of hurricane-prediction models. The most innovative aspect of the CBLAST-Hurricane modeling effort is the development and testing of a fully coupled atmosphere–wave–ocean modeling system that is capable of resolving the eye and eyewall at ~1-km grid resolution, which is consistent with a key recommendation for the next-generation hurricane-prediction models by the NOAA Science Advisor Board Hurricane Intensity Research Working Group. It is also the National Centers for Environmental Prediction (NCEP) plan for the new Hurricane Weather Research and Forecasting (HWRF) model to be implemented operationally in 2007–08.
    Description: The CBLAST-Hurricane is a research program supported by a departmental research initiative at the Office of Naval Research (ONR). The research is supported by ONR Research Grants N00014-01-1-0156, N00014-04-1-0109, N00014-01-F-0052, and SBIR for the EM-APEX development and deployment.
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  • 150
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 20 (2007): 3395-3410, doi:10.1175/JCLI4195.1
    Description: Using 40-yr ECMWF Re-Analysis (ERA-40) data and in situ observations, the positive trend of Southern Ocean surface wind stress during two recent decades is detected, and its close linkage with spring Antarctic ozone depletion is established. The spring Antarctic ozone depletion affects the Southern Hemisphere lower-stratospheric circulation in late spring/early summer. The positive feedback involves the strengthening and cooling of the polar vortex, the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients, the acceleration of the circumpolar westerlies, and the reduction of the upward wave flux. This feedback loop, together with the ozone-related photochemical interaction, leads to the upward tendency of lower-stratospheric zonal wind in austral summer. In addition, the stratosphere–troposphere coupling, facilitated by ozone-related dynamics and the Southern Annular Mode, cooperates to relay the zonal wind anomalies to the upper troposphere. The wave–mean flow interaction and the meridional circulation work together in the form of the Southern Annular Mode, which transfers anomalous wind signals downward to the surface, triggering a striking strengthening of surface wind stress over the Southern Ocean.
    Description: This study was supported by MOST of China (Grant 2006CB403604) and Chinese Academy of Sciences (Grant KZSW2-YW-214) (for YXY and DXW) and W. Alan Clark Chair from Woods Hole Oceanographic Institution (for RXH).
    Keywords: Wind stress ; Decadal variability ; Ozone ; Southern Ocean ; Stratospheric circulation
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  • 151
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 24 (2007): 1117-1130, doi:10.1175/JTECH2016.1.
    Description: Sensor response corrections for two models of Sea-Bird Electronics, Inc., conductivity–temperature–depth (CTD) instruments (the SBE-41CP and SBE-41) designed for low-energy profiling applications were estimated and applied to oceanographic data. Three SBE-41CP CTDs mounted on prototype ice-tethered profilers deployed in the Arctic Ocean sampled diffusive thermohaline staircases and telemetered data to shore at their full 1-Hz resolution. Estimations of and corrections for finite thermistor time response, time shifts between when a parcel of water was sampled by the thermistor and when it was sampled by the conductivity cell, and the errors in salinity induced by the thermal inertia of the conductivity cell are developed with these data. In addition, thousands of profiles from Argo profiling floats equipped with SBE-41 CTDs were screened to select examples where thermally well-mixed surface layers overlaid strong thermoclines for which standard processing often yields spuriously fresh salinity estimates. Hundreds of profiles so identified are used to estimate and correct for the conductivity cell thermal mass error in SBE-41 CTDs.
    Description: The National Ocean Partnership Program and the National Oceanic and Atmospheric Administration (NOAA) Office of Oceanic and Atmospheric Research funded this analysis. The ITP data were acquired under National Science Foundation (NSF) Grant OCE0324233.
    Keywords: Instrumentation ; Profilers ; Salinity
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  • 152
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 24 (2007): 102-116, doi:10.1175/JTECH1953.1.
    Description: Measurements of the vertical Reynolds stress components in the wave-dominated nearshore are required to diagnose momentum and turbulence dynamics. Removing wave bias from Reynolds stress estimates is critical to a successful diagnosis. Here two existing Reynolds stress estimation methods (those of Trowbridge, and Shaw and Trowbridge) for wave-dominated environments and an extended method (FW) that is a combination of the two are tested with a vertical array of three current meters deployed in 3.2-m water depth off an ocean beach. During the 175-h-long experiment the instruments were seaward of the surfzone and the alongshore current was wind driven. Intercomparison of Reynolds stress methods reveals that the Trowbridge method is wave bias dominated. Tests of the integrated cospectra are used to reject bad Reynolds stress estimates, and the Shaw and Trowbridge estimates are rejected more often than FW estimates. With the FW method, wave bias remains apparent in the cross-shore component of the Reynolds stress. However, the alongshore component of Reynolds stress measured at the three current meters are related to each other with a vertically uniform first EOF containing 73% of the variance, indicating the presence of a constant stress layer. This is the first time the vertical structure of Reynolds stress has been measured in a wave-dominated environment. The Reynolds stress is, albeit weakly, related to the wind stress and a parameterized bottom stress. Using derived wave bias and bottom stress parameterizations, the effect of wave bias on Reynolds stress estimates is shown to be weaker for more typical surfzone conditions (with both stronger waves and currents than those observed here).
    Description: Funded by NSF, ONR, and NOPP.
    Keywords: Waves, oceanic ; Stress ; Sensors
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  • 153
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 24 (2007): 1050-1065, doi:10.1175/JTECH2027.1.
    Description: Results are presented from a pilot study using a fluorescent dye tracer imaged by airborne lidar in the ocean surface layer on spatial scales of meters to kilometers and temporal scales of minutes to hours. The lidar used here employs a scanning, frequency-doubled Nd:YAG laser to emit an infrared (1064 nm) and green (532 nm) pulse 6 ns in duration at a rate of 1 kHz. The received signal is split to infrared, green, and fluorescent (nominally 580–600 nm) channels, the latter two of which are used to compute absolute dye concentration as a function of depth and horizontal position. Comparison of dye concentrations inferred from the lidar with in situ fluorometry measurements made by ship shows good agreement both qualitatively and quantitatively for absolute dye concentrations ranging from 1 to 〉10 ppb. Uncertainties associated with horizontal variations in the natural seawater attenuation are approximately 1 ppb. The results demonstrate the ability of airborne lidar to capture high-resolution three-dimensional “snapshots” of the distribution of the tracer as it evolves over very short time and space scales. Such measurements offer a powerful observational tool for studies of transport and mixing on these scales.
    Description: Support was provided by the Cecil H. and Ida M. Green Technology Innovation Fund under Grant 27001545, the Office of Naval Research Grant N00014-01-1-0984, and the Woods Hole Oceanographic Institution Coastal Ocean Institute.
    Keywords: Lidars ; In situ observations ; Aircraft observations
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  • 154
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 1001-1021, doi:10.1175/jpo3034.1.
    Description: The nonlinear dynamics of baroclinically unstable waves in a time-dependent zonal shear flow is considered in the framework of the two-layer Phillips model on the beta plane. In most cases considered in this study the amplitude of the shear is well below the critical value of the steady shear version of the model. Nevertheless, the time-dependent problem in which the shear oscillates periodically is unstable, and the unstable waves grow to substantial amplitudes, in some cases with strongly nonlinear and turbulent characteristics. For very small values of the shear amplitude in the presence of dissipation an analytical, asymptotic theory predicts a self-sustained wave whose amplitude undergoes a nonlinear oscillation whose period is amplitude dependent. There is a sensitive amplitude dependence of the wave on the frequency of the oscillating shear when the shear amplitude is small. This behavior is also found in a truncated model of the dynamics, and that model is used to examine larger shear amplitudes. When there is a mean value of the shear in addition to the oscillating component, but such that the total shear is still subcritical, the resulting nonlinear states exhibit a rectified horizontal buoyancy flux with a nonzero time average as a result of the instability of the oscillating shear. For higher, still subcritical, values of the shear, a symmetry breaking is detected in which a second cross-stream mode is generated through an instability of the unstable wave although this second mode would by itself be stable on the basic time-dependent current. For shear values that are substantially subcritical but of order of the critical shear, calculations with a full quasigeostrophic numerical model reveal a turbulent flow generated by the instability. If the beta effect is disregarded, the inviscid, linear problem is formally stable. However, calculations show that a small degree of nonlinearity is enough to destabilize the flow, leading to large amplitude vacillations and turbulence. When the most unstable wave is not the longest wave in the system, a cascade up scale to longer waves is observed. Indeed, this classically subcritical flow shows most of the qualitative character of a strongly supercritical flow. This result supports previous suggestions of the important role of background time dependence in maintaining the atmospheric and oceanic synoptic eddy field.
    Description: GRF was supported by NSF Grant OCE-0137023, and JP was supported by NSF Grant OCE- 9901654.
    Keywords: Baroclinic currents ; Shear flows ; Wave instability ; Oscillating shear ; Time dependence
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  • 155
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 1103-1121, doi:10.1175/jpo3041.1.
    Description: The role of mesoscale oceanic eddies is analyzed in a quasigeostrophic coupled ocean–atmosphere model operating at a large Reynolds number. The model dynamics are characterized by decadal variability that involves nonlinear adjustment of the ocean to coherent north–south shifts of the atmosphere. The oceanic eddy effects are diagnosed by the dynamical decomposition method adapted for nonstationary external forcing. The main effects of the eddies are an enhancement of the oceanic eastward jet separating the subpolar and subtropical gyres and a weakening of the gyres. The flow-enhancing effect is due to nonlinear rectification driven by fluctuations of the eddy forcing. This is a nonlocal process involving generation of the eddies by the flow instabilities in the western boundary current and the upstream part of the eastward jet. The eddies are advected by the mean current to the east, where they backscatter into the rectified enhancement of the eastward jet. The gyre-weakening effect, which is due to the time-mean buoyancy component of the eddy forcing, is a result of the baroclinic instability of the westward return currents. The diagnosed eddy forcing is parameterized in a non-eddy-resolving ocean model, as a nonstationary random process, in which the corresponding parameters are derived from the control coupled simulation. The key parameter of the random process—its variance—is related to the large-scale flow baroclinicity index. It is shown that the coupled model with the non-eddy-resolving ocean component and the parameterized eddies correctly simulates climatology and low-frequency variability of the control eddy-resolving coupled solution.
    Description: Funding for this work came from NSF Grants OCE 02-221066 and OCE 03-44094. Additional funding for PB was provided by the U.K. Royal Society Fellowship and by WHOI Grants 27100056 and 52990035.
    Keywords: Ocean dynamics ; Ocean models ; Eddies ; Jets ; Coupled models
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  • 156
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 1764-1777, doi:10.1175/jpo3098.1.
    Description: The vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region (3.2-m mean water depth) with a tripod of three acoustic Doppler current meters off a sandy ocean beach. Surface and bottom boundary layer dissipation scaling concepts overlap in this region. No depth-limited wave breaking occurred at the tripod, but wind-induced whitecapping wave breaking did occur. Dissipation is maximum near the surface and minimum at middepth, with a secondary maximum near the bed. The observed dissipation does not follow a surfzone scaling, nor does it follow a “log layer” surface or bottom boundary layer scaling. At the upper two current meters, dissipation follows a modified deep-water breaking-wave scaling. Vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation, implying that the vertical diffusion of turbulence is important. The increased near-bed secondary dissipation maximum results from a decrease in the turbulent length scale.
    Description: Funding was provided by NSF and ONR.
    Keywords: Turbulence ; Kinetic energy ; Ocean
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  • 157
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 1859-1877, doi:10.1175/jpo3088.1.
    Description: A series of dye releases in the Hudson River estuary elucidated diapycnal mixing rates and temporal variability over tidal and fortnightly time scales. Dye was injected in the bottom boundary layer for each of four releases during different phases of the tide and of the spring–neap cycle. Diapycnal mixing occurs primarily through entrainment that is driven by shear production in the bottom boundary layer. On flood the dye extended vertically through the bottom mixed layer, and its concentration decreased abruptly near the base of the pycnocline, usually at a height corresponding to a velocity maximum. Boundary layer growth is consistent with a one-dimensional, stress-driven entrainment model. A model was developed for the vertical structure of the vertical eddy viscosity in the flood tide boundary layer that is proportional to u2*/N∞, where u* and N∞ are the bottom friction velocity and buoyancy frequency above the boundary layer. The model also predicts that the buoyancy flux averaged over the bottom boundary layer is equal to 0.06N∞u2* or, based on the structure of the boundary layer equal to 0.1NBLu2*, where NBL is the buoyancy frequency across the flood-tide boundary layer. Estimates of shear production and buoyancy flux indicate that the flux Richardson number in the flood-tide boundary layer is 0.1–0.18, consistent with the model indicating that the flux Richardson number is between 0.1 and 0.14. During ebb, the boundary layer was more stratified, and its vertical extent was not as sharply delineated as in the flood. During neap tide the rate of mixing during ebb was significantly weaker than on flood, owing to reduced bottom stress and stabilization by stratification. As tidal amplitude increased ebb mixing increased and more closely resembled the boundary layer entrainment process observed during the flood. Tidal straining modestly increased the entrainment rate during the flood, and it restratified the boundary layer and inhibited mixing during the ebb.
    Description: The work was supported by the National Science Foundation Grant OCE00-95972 (W. Geyer, J. Lerczak), OCE00-99310 (R. Houghton), and OCE00-95913 (R. Chant, E. Hunter).
    Keywords: Estuaries ; Boundary layer ; Mixing ; Tides ; Friction
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  • 158
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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. 37 (2007): 2509-2533, doi:10.1175/JPO3123.1.
    Description: Twelve years of historical hydrographic data, spanning the period 1990–2001, are analyzed to examine the along-stream evolution of the western North Atlantic Ocean shelfbreak front and current, following its path between the west coast of Greenland and the Middle Atlantic Bight. Over 700 synoptic sections are used to construct a mean three-dimensional description of the summer shelfbreak front and to quantify the along-stream evolution in properties, including frontal strength and grounding position. Results show that there are actually two fronts in the northern part of the domain—a shallow front located near the shelf break and a deeper front centered in the core of Irminger Water over the upper slope. The properties of the deeper Irminger front erode gradually to the south, and the front disappears entirely near the Grand Banks of Newfoundland. The shallow shelfbreak front is identifiable throughout the domain, and its properties exhibit large variations from north to south, with the largest changes occurring near the Tail of the Grand Banks. Despite these structural changes, and large variations in topography, the foot of the shelfbreak front remains within 20 km of the shelf break. The hydrographic sections are also used to examine the evolution of the baroclinic velocity field and its associated volume transport. The baroclinic velocity structure consists of a single velocity core that is stronger and penetrates deeper where the Irminger front is present. The baroclinic volume transport decreases by equal amounts at the southern end of the Labrador Shelf and at the Tail of the Grand Banks. Overall, the results suggest that the Grand Banks is a geographically critical location in the North Atlantic shelfbreak system.
    Description: This work was supported by the National Science Foundation under Grants OCE00- 95261 (PF) and OCE-0450658 (RP).
    Keywords: Continental shelf ; Currents ; Atlantic Ocean ; Fronts ; Transport
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  • 159
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 1092–1097, doi:10.1175/JPO3045.1.
    Description: The impact of the observed relationship between sea surface temperature and surface wind stress on baroclinic instability in the ocean is explored using linear theory and a nonlinear model. A simple parameterization of the influence of sea surface temperature on wind stress is used to derive a surface boundary condition for the vertical velocity at the base of the oceanic Ekman layer. This boundary condition is applied to the classic linear, quasigeostrophic stability problem for a uniformly sheared flow originally studied by Eady in the 1940s. The results demonstrate that for a wind directed from warm water toward cold water, the coupling acts to enhance the growth rate, and increase the wavelength, of the most unstable wave. Winds in the opposite sense reduce the growth rate and decrease the wavelength of the most unstable wave. For representative coupling strengths, the change in growth rate can be as large as ±O(50%). This effect is largest for shallow, strongly stratified, low-latitude flows.
    Description: This work was supported by the Office of Naval Research Grant N00014-05-1-0300.
    Keywords: Wind stress ; Instability ; Sea surface temperature ; Baroclinic flows ; Ocean dynamics
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  • 160
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 1177-1191, doi:10.1175/jpo3054.1.
    Description: The stability of baroclinic Rossby waves in large ocean basins is examined, and the quasigeostrophic (QG) results of LaCasce and Pedlosky are generalized. First, stability equations are derived for perturbations on large-scale waves, using the two-layer shallow-water system. These equations resemble the QG stability equations, except that they retain the variation of the internal deformation radius with latitude. The equations are solved numerically for different initial conditions through eigenmode calculations and time stepping. The fastest-growing eigenmodes are intensified at high latitudes, and the slower-growing modes are intensified at lower latitudes. All of the modes have meridional scales and growth times that are comparable to the deformation radius in the latitude range where the eigenmode is intensified. This is what one would expect if one had applied QG theory in latitude bands. The evolution of large-scale waves was then simulated using the Regional Ocean Modeling System primitive equation model. The results are consistent with the theoretical predictions, with deformation-scale perturbations growing at rates inversely proportional to the local deformation radius. The waves succumb to the perturbations at the mid- to high latitudes, but are able to cross the basin at low latitudes before doing so. Also, the barotropic waves produced by the instability propagate faster than the baroclinic long-wave speed, which may explain the discrepancy in speeds noted by Chelton and Schlax.
    Description: PEI was supported by a postdoctoral grant from the Norwegian Research Council, JHL was supported under the Norwegian NOCLIM II program, and JP was partly supported by NSF OCE 0451086.
    Keywords: Rossby waves ; Ocean models ; Barotropic flows ; Baroclinic flows
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  • 161
    facet.materialart.
    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. 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 37 (2007): 2158–2171, doi:10.1175/jpo3100.1.
    Description: The triad instability of the large-scale, first-mode, baroclinic Rossby waves is studied in the context of the planetary scale when the Coriolis parameter is to its lowest order varying with latitude. Accordingly, rather than remain constant as in quasigeostrophic theory, the deformation radius also changes with latitude, yielding new and interesting features to the propagation and triad instability processes. On the planetary scale, baroclinic waves vary their meridional wavenumbers along group velocity rays while they conserve both frequencies and zonal wavenumbers. The amplitudes of both barotropic and baroclinic waves would change with latitude along a ray path in the same way that the Coriolis parameter does if effects of the nonlinear interaction are ignored. The triad interaction for a specific triad is localized within a small latitudinal band where the resonance conditions are satisfied and quasigeostrophic theory is applicable locally. Using the growth rate from that theory as a measure, at each latitude along the ray path of the basic wave, a barotropic wave and a secondary baroclinic wave are picked up to form the most unstable triad and the distribution of this maximum growth rate is examined. It is found to increase southward under the assumption that triad interactions do not cause a noticeable decrease in the quantity of the basic wave’s amplitude divided by the Coriolis parameter. Different barotropic waves that maximize the growth rate at different latitudes have almost the same meridional length scale, on the order of the deformation radius. With many rays starting from different latitudes on the eastern boundary and with wavenumbers on each of them satisfying the no-normal-flow condition, the resulting two-dimensional distribution of the growth rate is a complicated function of the relative relations of zonal wavenumbers or frequencies on different rays and the orientation of the eastern boundary. In general, the growth rate is largest on rays originating to the north.
    Description: This research was supported in part by NSF OCE 0451086 and by the MIT/WHOI Joint Program in Physical Oceanography.
    Keywords: Rossby waves ; Planetary waves ; Waves, oceanic
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  • 162
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 392–409, doi:10.1175/JCLI3620.1.
    Description: Data from the Eastern Pacific Investigation of Climate Studies (EPIC) mooring array are used to evaluate the annual cycle of surface cloud forcing in the far eastern Pacific stratus cloud deck/cold tongue/intertropical convergence zone complex. Data include downwelling surface solar and longwave radiation from 10 EPIC-enhanced Tropical Atmosphere Ocean (TAO) moorings from 8°S, 95°W to 12°N, 95°W, and the Woods Hole Improved Meteorology (IMET) mooring in the stratus cloud deck region at 20°S, 85°W. Surface cloud forcing is defined as the observed downwelling radiation at the surface minus the clear-sky value. Solar cloud forcing and longwave cloud forcing are anticorrelated at all latitudes from 12°N to 20°S: clouds tended to reduce the downward solar radiation and to a lesser extent increase the downward longwave radiation at the surface. The relative amount of solar radiation reduction and longwave increase depends upon cloud type and varies with latitude. A statistical relationship between solar and longwave surface cloud forcing is developed for rainy and dry periods and for the full record length in six latitudinal regions: northeast tropical warm pool, ITCZ, frontal zone, cold tongue, southern, and stratus deck regions. The buoy cloud forcing observations and empirical relations are compared with the International Satellite Cloud Climatology Project (ISCCP) radiative flux data (FD) dataset and are used as benchmarks to evaluate surface cloud forcing in the NCEP Reanalysis 2 (NCEP2) and 40-yr ECMWF Re-Analysis (ERA-40). ERA-40 and NCEP2 cloud forcing (both solar and longwave) showed large discrepancies with observations, being too large in the ITCZ and equatorial regions and too weak under the stratus deck at 20°S and north to the equator during the cool season from July to December. In particular the NCEP2 cloud forcing at the equator was nearly identical to the ITCZ region and thus had significantly larger solar cloud forcing and smaller longwave cloud forcing than observed. The net result of the solar and longwave cloud forcing deviations is that there is too little radiative warming in the ITCZ and southward to 8°S during the warm season and too much radiative warming under the stratus deck at 20°S and northward to the equator during the cold season.
    Description: This research was supported by grants from the NOAA Office of Global Programs, Pan American Climate Studies.
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  • 163
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 87 (2006): 1223–1225, doi:10.1175/BAMS-87-9-1223.
    Description: The importance of decadal climate variability (DCV) research is being increasingly recognized, including by international research programs such as the World Climate Research Program (WCRP) and the U.S. National Research Council. This brief article (workshop presentations available online at www.DecVar.org/auditorium.php) summarizes a consensus view of a research community workshop attended by approximately 45 scientists. Gaps in our knowledge of DCV and its societal impacts were identified, as were areas of needed research and anticipated benefits of research. It is a major challenge to implement recommendations of this and other such workshops on climate research in this era of declining earth science budgets. Therefore, a phased implementation is recommended, with highest priority recommendations outlined in a sidebar to this summary.
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  • 164
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 3033–3054, doi:10.1175/JCLI3783.1.
    Description: A new 3D global coupled carbon–climate model is presented in the framework of the Community Climate System Model (CSM-1.4). The biogeochemical module includes explicit land water–carbon coupling, dynamic carbon allocation to leaf, root, and wood, prognostic leaf phenology, multiple soil and detrital carbon pools, oceanic iron limitation, a full ocean iron cycle, and 3D atmospheric CO2 transport. A sequential spinup strategy is utilized to minimize the coupling shock and drifts in land and ocean carbon inventories. A stable, 1000-yr control simulation [global annual mean surface temperature ±0.10 K and atmospheric CO2 ± 1.2 ppm (1σ)] is presented with no flux adjustment in either physics or biogeochemistry. The control simulation compares reasonably well against observations for key annual mean and seasonal carbon cycle metrics; regional biases in coupled model physics, however, propagate clearly into biogeochemical error patterns. Simulated interannual-to-centennial variability in atmospheric CO2 is dominated by terrestrial carbon flux variability, ±0.69 Pg C yr−1 (1σ global net annual mean), which in turn reflects primarily regional changes in net primary production modulated by moisture stress. Power spectra of global CO2 fluxes are white on time scales beyond a few years, and thus most of the variance is concentrated at high frequencies (time scale 〈4 yr). Model variability in air–sea CO2 fluxes, ±0.10 Pg C yr−1 (1σ global annual mean), is generated by variability in sea surface temperature, wind speed, export production, and mixing/upwelling. At low frequencies (time scale 〉20 yr), global net ocean CO2 flux is strongly anticorrelated (0.7–0.95) with the net CO2 flux from land; the ocean tends to damp (20%–25%) slow variations in atmospheric CO2 generated by the terrestrial biosphere. The intrinsic, unforced natural variability in land and ocean carbon storage is the “noise” that complicates the detection and mechanistic attribution of contemporary anthropogenic carbon sinks.
    Description: This work was supported by NCAR, NSF ATM-9987457, NASA EOS-IDS Grant NAG5-9514, NASA Carbon Cycle Program Grant NAG5-11200, Lawrence Berkeley National Laboratory LDRD, and the WHOI Ocean and Climate Change Institute.
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  • 165
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 2122–2143, doi:10.1175/JCLI3761.1.
    Description: The Community Climate System Model version 3 (CCSM3) has recently been developed and released to the climate community. CCSM3 is a coupled climate model with components representing the atmosphere, ocean, sea ice, and land surface connected by a flux coupler. CCSM3 is designed to produce realistic simulations over a wide range of spatial resolutions, enabling inexpensive simulations lasting several millennia or detailed studies of continental-scale dynamics, variability, and climate change. This paper will show results from the configuration used for climate-change simulations with a T85 grid for the atmosphere and land and a grid with approximately 1° resolution for the ocean and sea ice. The new system incorporates several significant improvements in the physical parameterizations. The enhancements in the model physics are designed to reduce or eliminate several systematic biases in the mean climate produced by previous editions of CCSM. These include new treatments of cloud processes, aerosol radiative forcing, land–atmosphere fluxes, ocean mixed layer processes, and sea ice dynamics. There are significant improvements in the sea ice thickness, polar radiation budgets, tropical sea surface temperatures, and cloud radiative effects. CCSM3 can produce stable climate simulations of millennial duration without ad hoc adjustments to the fluxes exchanged among the component models. Nonetheless, there are still systematic biases in the ocean–atmosphere fluxes in coastal regions west of continents, the spectrum of ENSO variability, the spatial distribution of precipitation in the tropical oceans, and continental precipitation and surface air temperatures. Work is under way to extend CCSM to a more accurate and comprehensive model of the earth's climate system.
    Description: We would like to acknowledge the substantial contributions to and support for the CCSM project from the National Science Foundation (NSF), the Department of Energy (DOE), the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration.
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  • 166
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2005. 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 22 (2005): 583–591, doi:10.1175/JTECH1731.1.
    Description: The algorithm used to transform velocity signals from beam coordinates to earth coordinates in an acoustic Doppler current profiler (ADCP) relies on the assumption that the currents are uniform over the horizontal distance separating the beams. This condition may be violated by (nonlinear) internal waves, which can have wavelengths as small as 100–200 m. In this case, the standard algorithm combines velocities measured at different phases of a wave and produces horizontal velocities that increasingly differ from true velocities with distance from the ADCP. Observations made in Massachusetts Bay show that currents measured with a bottom-mounted upward-looking ADCP during periods when short-wavelength internal waves are present differ significantly from currents measured by point current meters, except very close to the instrument. These periods are flagged with high error velocities by the standard ADCP algorithm. In this paper measurements from the four spatially diverging beams and the backscatter intensity signal are used to calculate the propagation direction and celerity of the internal waves. Once this information is known, a modified beam-to-earth transformation that combines appropriately lagged beam measurements can be used to obtain current estimates in earth coordinates that compare well with pointwise measurements.
    Description: A. Scotti was partially supported by ONR Grants N00014-03-1-0553 and N00014-01-1- 0172, B. Butman and P. Alexander by the U.S. Geological Survey, and R. Beardsley by the WHOI Smith Chair and ONR Grant N00014-98-1-0210. S. Anderson received partial support from ONR (Grant N00014-97- 1-0158). The Massachusetts Bay Internal Wave Experiment was jointly supported by ONR and USGS.
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  • 167
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 3337–3353, doi:10.1175/JCLI3800.1.
    Description: Eleven coupled climate–carbon cycle models used a common protocol to study the coupling between climate change and the carbon cycle. The models were forced by historical emissions and the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A2 anthropogenic emissions of CO2 for the 1850–2100 time period. For each model, two simulations were performed in order to isolate the impact of climate change on the land and ocean carbon cycle, and therefore the climate feedback on the atmospheric CO2 concentration growth rate. There was unanimous agreement among the models that future climate change will reduce the efficiency of the earth system to absorb the anthropogenic carbon perturbation. A larger fraction of anthropogenic CO2 will stay airborne if climate change is accounted for. By the end of the twenty-first century, this additional CO2 varied between 20 and 200 ppm for the two extreme models, the majority of the models lying between 50 and 100 ppm. The higher CO2 levels led to an additional climate warming ranging between 0.1° and 1.5°C. All models simulated a negative sensitivity for both the land and the ocean carbon cycle to future climate. However, there was still a large uncertainty on the magnitude of these sensitivities. Eight models attributed most of the changes to the land, while three attributed it to the ocean. Also, a majority of the models located the reduction of land carbon uptake in the Tropics. However, the attribution of the land sensitivity to changes in net primary productivity versus changes in respiration is still subject to debate; no consensus emerged among the models.
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  • 168
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 6153–6169, doi:10.1175/JCLI3970.1.
    Description: The present study used a new net surface heat flux (Qnet) product obtained from the Objective Analyzed Air–Sea Fluxes (OAFlux) project and the International Satellite Cloud Climatology Project (ISCCP) to examine two specific issues—one is to which degree Qnet controls seasonal variations of sea surface temperature (SST) in the tropical Atlantic Ocean (20°S–20°N, east of 60°W), and the other is whether the physical relation can serve as a measure to evaluate the physical representation of a heat flux product. To better address the two issues, the study included the analysis of three additional heat flux products: the Southampton Oceanographic Centre (SOC) heat flux analysis based on ship reports, and the model fluxes from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis and the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). The study also uses the monthly subsurface temperature fields from the World Ocean Atlas to help analyze the seasonal changes of the mixed layer depth (hMLD). The study showed that the tropical Atlantic sector could be divided into two regimes based on the influence level of Qnet. SST variability poleward of 5°S and 10°N is dominated by the annual cycle of Qnet. In these regions the warming (cooling) of the sea surface is highly correlated with the increased (decreased) Qnet confined in a relatively shallow (deep) hMLD. The seasonal evolution of SST variability is well predicted by simply relating the local Qnet with a variable hMLD. On the other hand, the influence of Qnet diminishes in the deep Tropics within 5°S and 10°N and ocean dynamic processes play a dominant role. The dynamics-induced changes in SST are most evident along the two belts, one of which is located on the equator and the other off the equator at about 3°N in the west, which tilts to about 10°N near the northwestern African coast. The study also showed that if the degree of consistency between the correlation relationships of Qnet, hMLD, and SST variability serves as a measure of the quality of the Qnet product, then the Qnet from OAFlux + ISCCP and ERA-40 are most physically representative, followed by SOC. The NCEP–NCAR Qnet is least representative. It should be noted that the Qnet from OAFlux + ISCCP and ERA-40 have a quite different annual mean pattern. OAFlux + ISCCP agrees with SOC in that the tropical Atlantic sector gains heat from the atmosphere on the annual mean basis, where the ERA-40 and the NCEP–NCAR model reanalyses indicate that positive Qnet occurs only in the narrow equatorial band and in the eastern portion of the tropical basin. Nevertheless, seasonal variances of the Qnet from OAFlux + ISCCP and ERA-40 are very similar once the respective mean is removed, which explains why the two agree with each other in accounting for the seasonal variability of SST. In summary, the study suggests that an accurate estimation of surface heat flux is crucially important for understanding and predicting SST fluctuations in the tropical Atlantic Ocean. It also suggests that future emphasis on improving the surface heat flux estimation should be placed more on reducing the mean bias.
    Description: This study is support by the NOAA CLIVAR Atlantic under Grant NA06GP0453 and NOAA Climate observations and Climate Change and Data Detection under Grant NA17RJ1223.
    Keywords: Sea surface temperature ; Surface fluxes ; Seasonal variability
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  • 169
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 5366–5387, doi:10.1175/JCLI3892.1.
    Description: The oceanic Ekman transport and pumping are among the most important parameters in studying the ocean general circulation and its variability. Upwelling due to the Ekman transport divergence has been identified as a leading mechanism for the seasonal to interannual variability of the upper-ocean heat content in many parts of the World Ocean, especially along coasts and the equator. Meanwhile, the Ekman pumping is the primary mechanism that drives basin-scale circulations in subtropical and subpolar oceans. In those ice-free oceans, the Ekman transport and pumping rate are calculated using the surface wind stress. In the ice-covered Arctic Ocean, the surface momentum flux comes from both air–water and ice–water stresses. The data required to compute these stresses are now available from satellite and buoy observations. But no basin-scale calculation of the Ekman transport in the Arctic Ocean has been done to date. In this study, a suite of satellite and buoy observations of ice motion, ice concentration, surface wind, etc., will be used to calculate the daily Ekman transport over the whole Arctic Ocean from 1978 to 2003 on a 25-km resolution. The seasonal variability and its relationship to the surface forcing fields will be examined. Meanwhile, the contribution of the Ekman transport to the seasonal fluxes of heat and salt to the Arctic Ocean mixed layer will be discussed. It was found that the greatest seasonal variations of Ekman transports of heat and salt occur in the southern Beaufort Sea in the fall and early winter when a strong anticyclonic wind and ice motion are present. The Ekman pumping velocity in the interior Beaufort Sea reaches as high as 10 cm day−1 in November while coastal upwelling is even stronger. The contributions of the Ekman transport to the heat and salt flux in the mixed layer are also considerable in the region.
    Description: This study has been supported by NASA Cryospheric Science Program (Grant NNG04GP34G) and by the NSF Office of Polar Program (Grant OPP0424074).
    Keywords: Seasonal variability ; Ocean ; Mixed layer ; Heat flux
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  • 170
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2005. 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 22 (2005): 1267–1281, doi:10.1175/JTECH1760.1.
    Description: The focus of this paper is on the development of methodology for short-term (1–3 days) oceanic bioluminescence (BL) predictions and the optimization of spatial and temporal bioluminescence sampling strategies. The approach is based on predictions of bioluminescence with an advection–diffusion–reaction (tracer) model with velocities and diffusivities from a circulation model. In previous research, it was shown that short-term changes in some of the salient features in coastal bioluminescence can be explained and predicted by using this approach. At the same time, it was demonstrated that optimization of bioluminescence sampling prior to the forecast is critical for successful short-term BL predictions with the tracer model. In the present paper, the adjoint to the tracer model is used to study the sensitivity of the modeled bioluminescence distributions to the sampling strategies for BL. The locations and times of bioluminescence sampling prior to the forecast are determined by using the adjoint-based sensitivity maps. The approach is tested with bioluminescence observations collected during August 2000 and 2003 in the Monterey Bay, California, area. During August 2000, BL surveys were collected during a strong wind relaxation event, while in August 2003, BL surveys were conducted during an extended (longer than a week) upwelling-favorable event. The numerical bioluminescence predictability experiments demonstrated a close agreement between observed and model-predicted short-term spatial and temporal changes of the coastal bioluminescence.
    Description: This work has been supported by the Ocean Optics and Biology and Physical Oceanography Programs of the Office of Naval Research. Shulman’s support is through the NRL “Use of a Circulation Model to Enhance Predictability of Bioluminescence in the Coastal Ocean” project sponsored by the Office of Naval Research.
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  • 171
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 5100–5121, doi:10.1175/JCLI3902.1.
    Description: Three interrelated climate phenomena are at the center of the Climate Variability and Predictability (CLIVAR) Atlantic research: tropical Atlantic variability (TAV), the North Atlantic Oscillation (NAO), and the Atlantic meridional overturning circulation (MOC). These phenomena produce a myriad of impacts on society and the environment on seasonal, interannual, and longer time scales through variability manifest as coherent fluctuations in ocean and land temperature, rainfall, and extreme events. Improved understanding of this variability is essential for assessing the likely range of future climate fluctuations and the extent to which they may be predictable, as well as understanding the potential impact of human-induced climate change. CLIVAR is addressing these issues through prioritized and integrated plans for short-term and sustained observations, basin-scale reanalysis, and modeling and theoretical investigations of the coupled Atlantic climate system and its links to remote regions. In this paper, a brief review of the state of understanding of Atlantic climate variability and achievements to date is provided. Considerable discussion is given to future challenges related to building and sustaining observing systems, developing synthesis strategies to support understanding and attribution of observed change, understanding sources of predictability, and developing prediction systems in order to meet the scientific objectives of the CLIVAR Atlantic program.
    Keywords: Atlantic Ocean ; Climate prediction ; Variational studies ; Tropical variability ; North Atlantic Oscillation
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  • 172
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society 2006. 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 19 (2006): 6391–6408, doi:10.1175/JCLI3976.1.
    Description: A novel mechanism of decadal midlatitude coupled variability, which crucially depends on the nonlinear dynamics of both the atmosphere and the ocean, is presented. The coupled model studied involves quasigeostrophic atmospheric and oceanic components, which communicate with each other via a constant-depth oceanic mixed layer. A series of coupled and uncoupled experiments show that the decadal coupled mode is active across parameter ranges that allow the bimodality of the atmospheric zonal flow to coexist with oceanic turbulence. The latter is most intense in the regions of inertial recirculation (IR). Bimodality is associated with the existence of two distinct anomalously persistent zonal-flow modes, which are characterized by different latitudes of the atmospheric jet stream. The IR reorganizations caused by transitions of the atmosphere from its high- to low-latitude state and vice versa create sea surface temperature anomalies that tend to induce transition to the opposite atmospheric state. The decadal–interdecadal time scale of the resulting oscillation is set by the IR adjustment; the latter depends most sensitively on the oceanic bottom drag. The period T of the nonlinear oscillation is 7–25 yr for the range of parameters explored, with the most realistic parameter values yielding T ≈ 20 yr. Aside from this nonlinear oscillation, an interannual Rossby wave mode is present in all coupled experiments. This coupled mode depends neither on atmospheric bimodality, nor on ocean eddy dynamics; it is analogous to the mode found previously in a channel configuration. Its time scale in the model with a closed ocean basin is set by cross-basin wave propagation and equals 3–5 yr for a basin width comparable with the North Atlantic.
    Description: This research was supported by NSF Grant OCE-02-221066 (all coauthors) and DOE Grant DE-FG-03-01ER63260 (MG and SK).
    Keywords: Climate variability ; Rossby waves ; Climate models
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  • 173
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 1245-1262, doi:10.1175/JPO2713.1.
    Description: Evidence is presented that lateral dispersion on scales of 1–10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small-scale geostrophic motions caused by patches of mixed fluid adjusting in the aftermath of diapycnal mixing events. Dye-release experiments conducted during the recent Coastal Mixing and Optics (CMO) experiment provide estimates of diapycnal and lateral dispersion. Microstructure observations made during these experiments showed patchy turbulence on vertical scales of 1–10 m and horizontal scales of a few hundred meters to a few kilometers. Momentum scaling and a simple random walk formulation were used to estimate the effective lateral dispersion caused by motions resulting from lateral adjustment following episodic mixing events. It is predicted that lateral dispersion is largest when the scale of mixed patches is on the order of the internal Rossby radius of deformation, which seems to have been the case for CMO. For parameter values relevant to CMO, lower-bound estimates of the effective lateral diffusivity by this mechanism ranged from 0.1 to 1 m2s−1. Revised estimates after accounting for the possibility of long-lived motions were an order of magnitude larger and ranged from 1 to 10 m2s−1. The predicted dispersion is large enough to explain the observed lateral dispersion in all four CMO dye-release experiments examined.
    Description: The Coastal Mixing and Optics dye studies were funded by the Office of Naval Research under Grants N00014-95-1-0633 (tracer experiments) and N00014-95-1-1063 (AASERT fellowship). Additional analysis was also performed under ONR Grant N00014-01-1-0984.
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  • 174
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 569–583, doi:10.1175/JPO2679.1.
    Description: When the salty and heavy water of the Red Sea exits from the Strait of Bab el Mandeb, it continues downslope into the Gulf of Aden mainly along two channels. The 130-km-long “Northern Channel” (NC) is topographically confined and is typically only 5 km wide. In it, the Red Sea plume shows unanticipated patterns of vertical structure, turbulent mixing, and entrainment. Above the seafloor a 25–120-m-thick weakly stratified layer shows little dilution along the channel. Hence this bottom layer undergoes only weak entrainment. In contrast, a 35–285-m-thick interfacial layer shows stronger entrainment and is shown in a companion paper to undergo vigorous turbulent mixing. It is thus the interface that exhibits the bulk of entrainment of the Red Sea plume in the NC. The interfacial layer also carries most of the overall plume transport, increasingly so with downstream distance. The “Southern Channel” (SC) is wider than the NC and is accessed from the latter by a sill about 33 m above the floor of the NC. Entrainment into the bottom layer of the SC is diagnosed to be strong near the entry into the SC such that the near-bottom density and salinity are smaller in the SC than in the NC at the same distance from Bab el Mandeb. In comparison with winter conditions, the authors encountered weaker outflow with shallower equilibration depths during the summer cruise. Bulk Froude numbers computed for the whole plume varied within the range 0.2–1. Local maxima occurred in relatively steep channel sections and coincided with locations of significant entrainment.
    Description: The Red Sea Outflow Experiment was funded by the National Science Foundation under Contracts OCE-9819506 and OCE-9818464. Additional support was provided to the “Climate Process Team Gravity Currents” under OCE-0336799.
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  • 175
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    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 1037-1053, doi:10.1175/JPO2734.1.
    Description: High-resolution hydrographic and velocity measurements across the East Greenland shelf break south of Denmark Strait have revealed an intense, narrow current banked against the upper continental slope. This is believed to be the result of dense water cascading over the shelf edge and entraining ambient water. The current has been named the East Greenland Spill Jet. It resides beneath the East Greenland/Irminger Current and transports roughly 2 Sverdrups of water equatorward. Strong vertical mixing occurs during the spilling, although the entrainment farther downstream is minimal. A vorticity analysis reveals that the increase in cyclonic relative vorticity within the jet is partly balanced by tilting vorticity, resulting in a sharp front in potential vorticity reminiscent of the Gulf Stream. The other components of the Irminger Sea boundary current system are described, including a presentation of absolute transports.
    Description: This project was funded by the National Science Foundation under Grant OCE 00-02492.
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  • 176
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 1305-1317, doi:10.1175/JPO2744.1.
    Description: An idealized theoretical model is developed for the acceleration of a two-dimensional, stratified current over a uniformly sloping bottom, driven by an imposed alongshelf pressure gradient and taking into account the effects of buoyancy advection in the bottom boundary layer. Both downwelling and upwelling pressure gradients are considered. For a specified pressure gradient, the model response depends primarily on the Burger number S = Nα/f, where N is the initial buoyancy frequency, α is the bottom slope, and f is the Coriolis parameter. Without stratification (S = 0), buoyancy advection is absent, and the alongshelf flow accelerates until bottom stress balances the imposed pressure gradient. The e-folding time scale to reach this steady state is the friction time, h/r, where h is the water depth and r is a linear bottom friction coefficient. With stratification (S ≠ 0), buoyancy advection in the bottom boundary layer produces vertical shear, which prevents the bottom stress from becoming large enough to balance the imposed pressure gradient for many friction time scales. Thus, the alongshelf flow continues to accelerate, potentially producing large velocities. The acceleration increases rapidly with increasing S, such that even relatively weak stratification (S 〉 0.2) has a major impact. These results are supported by numerical model calculations.
    Description: Funding was provided by the Division of Ocean Sciences of the National Science Foundation under Grant OCE-0241292. DCC also received some support from the Office of Naval Research under Grants N00014-00-1-0210 and N00014-02-1-0767.
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  • 177
    facet.materialart.
    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 1263–1278, doi:10.1175/JPO2743.1.
    Description: Multiple-gyre ocean models have a weaker mean subtropical circulation than single-gyre calculations with the same viscosity and subtropical forcing. Traditionally, this reduction in circulation is attributed to an intergyre eddy vorticity flux that cancels some of the wind input, part of which does not require a Lagrangian mass exchange (theory of dissipative meandering). Herein the intergyre eddy vorticity flux is shown to be a controlling factor in barotropic models at high Reynolds number only with exactly antisymmetric gyres and slip boundary conditions. Almost no intergyre flux occurs when no-slip boundary conditions are used, yet the subtropical gyre is still significantly weaker in multiple-gyre calculations. Sinuous modes of instability present only in multiple gyres are shown here to vastly increase the eddy vorticity transport efficiency. This increase in efficiency reduces the mean circulation necessary for equilibrium. With slip boundary conditions, the intergyre eddy transport is possibly much larger. However, with wind forcing relevant for the ocean—two unequal gyres—a mean flow flux of vorticity rather than an eddy flux between the regions of opposing wind forcing is increasingly important with increasing Reynolds number. A physical rationalization of the differing results is provided by diagnosis of the equilibrium vorticity budget and eddy transport efficiency. Calculations varying 1) boundary conditions, 2) sources and sinks of vorticity, 3) eddy transport efficiency, and 4) the degree of symmetry of the gyres are discussed.
    Description: The author was supported by an ONR-supported NDSEG fellowship, an MIT Presidential Fellowship, NSF OCE 9910654, a Princeton University/GFDL fellowship, and a NOAA Climate and Global Change postdoctoral fellowship managed by UCAR.
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  • 178
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 1568–1592, doi:10.1175/JPO2775.1.
    Description: Rotating two-layer exchange flow over a sill in a strait separating two relatively deep and wide basins is analyzed. Upstream of the sill in the deep upstream basin, the infinitely deep dense lower layer is assumed to be inactive, while the relatively thin upper layer flowing away from the sill forms a detached boundary current in the upstream basin. This analysis emphasizes the importance of this upstream boundary current, incorporating its width as a key parameter in a formalism for deducing the volume exchange rate and discriminating between maximal and submaximal states. Hence, even for narrow straits in which rotation does not dominate the dynamics within the strait, the importance of rotation in the wide upstream basin can be exploited. It is shown that the maximal allowable exchange transport through straits wider than 1½ Rossby deformation radii increases as rotation increases, unlike for smaller rotations, where the exchange decreases as rotation increases. The theory is applied to the exchange flow through the Strait of Gibraltar. This application illustrates how images of the oceans taken from space showing the width of the upstream flow, in this case a space shuttle photograph, might be used to determine the exchange transport through a strait. Maximal exchange conditions in the Strait of Gibraltar are predicted to apply at the time the space shuttle photograph was taken.
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  • 179
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 2487-2500, doi:10.1175/JPO2832.1.
    Description: The buoyancy-driven circulation of simple two-layer models on the β plane is studied in order to examine the role of beta in determining the magnitude and structure of the vertical motions forced in response to surface heating and cooling. Both analytical and numerical approaches are used to describe the change in circulation pattern and strength as a consequence of the planetary vorticity gradient. The physics is quasigeostrophic at lowest order but is sensitive to small nonquasigeostrophic mass fluxes across the boundary of the basin. The height of the interface between the two layers serves as an analog of temperature, and the vertical velocity at the interface consists of a cross-isopycnal velocity, modeled in terms of a relaxation to a prescribed interface height, as well as an adiabatic representation of eddy thickness fluxes parameterized as lateral diffusion of interface displacement. In the numerical model the lateral eddy diffusion of heat is explicitly represented by a resolved eddy field. In the plausibly more realistic case, when the lateral diffusion of buoyancy dominates the diffusion of momentum, the major vertical velocities occur at the boundary of the basin as in earlier f-plane studies. The effect of the planetary vorticity gradient is to intensify the sinking at the western wall and to enhance the magnitude of that sinking with respect to the f-plane models. The vertical mass flux in the Sverdrup interior exactly balances the vertical flux in the region of the strong horizontal transport of the western boundary current, leaving the net flux to occur in a very narrow region near the western boundary tucked well within the western boundary current. On the other hand, if the lateral diffusion of heat is arbitrarily and unrealistically eliminated, the vertical mass flux is forced to occur in the interior. The circulation pattern is extremely sensitive to small net inflows or outflows across the basin perimeter. The cross-basin flux determines the interface height on the basin’s eastern boundary and affects the circulation pattern across the entire basin.
    Description: This research was supported in part by grants from the National Science Foundation OCE-9901654 (JP) and OCE-0240978, and Office of Naval Research Grant N00014-03-0338 (MAS).
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  • 180
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 2187–2203, doi:10.1175/JPO2800.1.
    Description: The effect of breaking-wave-generated turbulence on the mean circulation, turbulence, and bottom stress in the surf zone is poorly understood. A one-dimensional vertical coupled turbulence (k–ε) and mean-flow model is developed that incorporates the effect of wave breaking with a time-dependent surface turbulence flux and uses existing (published) model closures. No model parameters are tuned to optimize model–data agreement. The model qualitatively reproduces the mean dissipation and production during the most energetic breaking-wave conditions in 4.5-m water depth off of a sandy beach and slightly underpredicts the mean alongshore current. By modeling a cross-shore transect case example from the Duck94 field experiment, the observed surf-zone dissipation depth scaling and the observed mean alongshore current (although slightly underpredicted) are generally reproduced. Wave breaking significantly reduces the modeled vertical shear, suggesting that surf-zone bottom stress cannot be estimated by fitting a logarithmic current profile to alongshore current observations. Model-inferred drag coefficients follow parameterizations (Manning–Strickler) that depend on the bed roughness and inversely on the water depth, although the inverse depth dependence is likely a proxy for some other effect such as wave breaking. Variations in the bed roughness and the percentage of breaking-wave energy entering the water column have a comparable effect on the mean alongshore current and drag coefficient. However, covarying the wave height, forcing, and dissipation and bed roughness separately results in an alongshore current (drag coefficient) only weakly (strongly) dependent on the bed roughness because of the competing effects of increased turbulence, wave forcing, and orbital wave velocities.
    Description: This work was funded by NSF, ONR, and NOPP.
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  • 181
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 238-254, doi:10.1175/JPO2848.1.
    Description: The seasonal variation of the North Equatorial Countercurrent (NECC) in the tropical Atlantic Ocean is investigated by using a linear, one-layer reduced-gravity ocean model and by analyzing sea surface height (SSH) data from Ocean Topography Experiment (TOPEX)/Poseidon (T/P) altimeters. The T/P data indicate that the seasonal variability of the NECC geostrophic transport, between 3° and 10°N, is dominated by SSH changes in the southern flank of the current. Since the southern boundary of the NECC is located partially within the equatorial waveguide, the SSH variation there can be influenced considerably by the equatorial dynamics. Therefore, it is hypothesized that the wind stress forcing along the equator is the leading driver for the seasonal cycle of the NECC transport. The wind stress curl in the NECC region is an important but smaller contributor. This hypothesis is tested by several sensitivity experiments that are designed to separate the two forcing mechanisms. In the first sensitivity run, a wind stress field that has a zero curl is used to force the ocean model. The result shows that the NECC geostrophic transport retains most of its seasonal variability. The same happens in another experiment in which the seasonal wind stress is applied only within a narrow band along the equator outside the NECC range. To further demonstrate the role of equatorial waves, another experiment was run in which the wind stress in the Southern Hemisphere is altered so that the model excludes hemispherically symmetrical waves (Kelvin waves and odd-numbered meridional modes of equatorial Rossby waves) and instead excites only the antisymmetrical equatorial Rossby modes. The circulation in the northern tropical ocean, including the NECC, is affected considerably even though the local wind stress there remains unchanged. All these appear to support the hypothesis presented in this paper.
    Description: This study is supported by NOAA OGP’s CLIVAR-Atlantic Program (authors J. Yang and T. Joyce: NOAA Grant NA16GP1573) and NASA Physical Oceanography Program (J. Yang: JPL Grant 1217578).
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  • 182
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 2387–2407, doi:10.1175/JPO2819.1.
    Description: According to observations, the Arctic Ocean circulation beneath a shallow thermocline can be schematized by cyclonic rim currents along shelves and over ridges. In each deep basin, the circulation is also believed to be cyclonic. This circulation pattern has been used as an important benchmark for validating Arctic Ocean models. However, modeling this grand circulation pattern with some of the most sophisticated ocean–ice models has been often difficult. The most puzzling and thus perhaps the most interesting finding from the Arctic Ocean Model Intercomparison Project (AOMIP), an international consortium that runs 14 Arctic Ocean models by using the identical forcing fields, is that its model results can be grouped into two nearly exact opposite patterns. While some models produce cyclonic circulation patterns similar to observations, others do the opposite. This study examines what could be possibly responsible for such strange inconsistency. It is found here that the flux of potential vorticity (PV) from the subarctic oceans strongly controls the circulation directions. For a semienclosed basin like the Arctic, the PV integral over the whole basin yields a balance between the net lateral PV inflow and the PV dissipation along the boundary. When an isopycnal layer receives a net positive PV through inflow/outflow, the circulation becomes cyclonic so that friction can generate a flux of negative PV to satisfy the integral balance. For simplicity, a barotropic ocean model is used in this paper but its application to the 3D models will be discussed. In the first set of experiments, the model with a realistic Arctic bathymetry is forced by observed inflows and outflows. In this case, there is a net positive PV inflow to the basin, due to the fact that inflow layer is thinner than that of outflow. The model produces a circulation field that is remarkably similar to the one from observations. In the second experiment, the model bathymetry at Fram Strait is modified so that the same inflows and outflows of water masses lead to a net negative PV flux into the Arctic. The circulation is reversed and becomes nearly the opposite of the first experiment. In the third experiment, the net PV flux is made to be zero by modifying again the sill depth at Fram Strait. The circulation becomes two gyres, a cyclonic one in the Eurasian Basin and an anticyclonic one in the Canada Basin. To elucidate the control of the PV integral, a second set of model experiments is conducted by using an idealized Arctic bathymetry so that the PV dynamics can be better explained without the complication of rough topography. The results from five additional experiments that used the idealized topography will be discussed. While the model used in this study is one layer, the same PV-integral constraint can be applied to any isopycnal layer in a three-dimensional model. Variables that affect the PV fluxes to this density layer at any inflow/outflow channel, such as layer thickness and water volume flux, can affect the circulation pattern. The relevance to 3D models is discussed in this paper.
    Description: This study is supported by the NSF Office of Polar Programs (OPP- 0424074) and the NASA Cryospheric Science Program (NA17RJ1223).
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  • 183
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 457-473, doi:10.1175/JPO2849.1.
    Description: Properties and seasonal evolution of North Pacific Ocean subtropical mode water (STMW) within and south of the Kuroshio Extension recirculation gyre are analyzed from profiling float data and additional hydrographic and shipboard ADCP measurements taken during 2004. The presence of an enhanced recirculation gyre and relatively low mesoscale eddy variability rendered this year favorable for the formation of STMW. Within the recirculation gyre, STMW formed from late-winter convection that reached depths greater than 450 m near the center of the gyre. The lower boundary of STMW, corresponding to σθ 25.5 kg m−3, was set by the maximum depth of the late-winter mixed layer. Properties within the deep portions of the STMW layer remained largely unchanged as the season progressed. In contrast, the upper boundary of the STMW layer eroded steadily as the seasonal thermocline deepened from late April to August. Vertical eddy diffusivity responsible for this erosion was estimated from a budget analysis of potential vorticity to be in the range of 2–5 × 10−4 m2 s−1. The latitudinal extent of the STMW formation was narrow, extending from 30°N to the Kuroshio Extension jet near 35°N. South of 30°N, STMW did not form locally but was transported from the recirculation gyre by lateral induction.
    Description: This study was supported by NSF as part of a Collaborative Research Project (OCE- 0220680 to UH, OCE-0221008 to URI, and OCE- 0220161 to WHOI).
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  • 184
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 395-411, doi:10.1175/JPO2857.1.
    Description: Irminger rings are warm-core eddies formed off the west coast of Greenland. Recent studies suggest that these eddies, which are implicated in the rapid springtime restratification of the Labrador Sea, are formed by an internal instability of the West Greenland Current (WGC), triggered by bathymetric variations. This study seeks to explore the effect of the magnitude and downstream length scale of bathymetric variations on the stability of a simple model of the WGC in a series of laboratory experiments in which a buoyant coastal current was allowed to flow over bathymetry consisting of piecewise constant slopes of varying magnitude. The currents did not form eddies over gently sloping bathymetry and only formed eddies over steep bathymetry if the current width exceeded the width of the sloping bathymetry. Eddying currents were immediately stabilized if they flowed onto gently sloping topography. Bathymetric variations that persisted only a short distance downstream perturbed the flow locally but did not lead to eddy formation. Eddies formed only once the downstream length of the bathymetric variations exceeded a critical scale of about 8 Rossby radii. These results are consistent with the observed behavior of the WGC, which begins to form Irminger rings after entering a region where the continental slope abruptly steepens and becomes narrower than the WGC itself in a region spanning about 20–80 Rossby radii of downstream distance.
    Description: The authors gratefully acknowledge the National Science Foundation (Grant OCE- 9810657) and the Office of Naval Research (Grant N00014-97-1-0934) for their support of the 2003 WHOI Geophysical Fluid Dynamics Summer School where much of the research presented in this paper was performed. CLW received additional support from the Office of Naval Research Grant N00014-98-1-0813.
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  • 185
    facet.materialart.
    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 606-628, doi:10.1175/JPO2875.1.
    Description: The seasonal and interannual variations in the export of Labrador Sea Water (LSW), and in the heat and freshwater transport through the central Labrador Sea, are examined for two different periods: from 1964 to 1974, using Ocean Weather Station Bravo data, and from 1996 to 2000, using data collected from profiling floats. A typical seasonal cycle involves a 300-m thickening of LSW (convection) followed by an equivalent thinning (restratification). Restratification is characterized by a drift of properties toward boundary current values that is indicative of a vigorous lateral exchange. The net result is a convergence of heat and salt, between 200 and 700 m, that balances the net surface heat loss to the atmosphere and partially offsets the surface freshwater accumulation due to surface, lateral exchange. Interannual variations in the export of LSW can be explained by taking into account changes in the central Labrador Sea–boundary current density gradient, which governs the lateral exchange. Interannual variations in how much heat is converged into the region, on the other hand, mostly reflect changes in the temperature of LSW. This only partly explains, however, the increased convergence of heat that occurs during the late 1990s. In years in which convection does not occur, restratification trends continue throughout the entire year, albeit at a reduced rate.
    Description: This work was supported by NSF Grant OCE 02-40978, the John E. and Anne W. Sawyer Endowed Fund, and the Grayce B. Kerr Fund.
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  • 186
    facet.materialart.
    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 967-996, doi:10.1175/JPO2876.1.
    Description: Surface expressions of internal tides constitute a significant component of the total recorded tide. The internal component is strongly modulated by the time-variable density structure, and the resulting perturbation of the recorded tide gives a welcome look at twentieth-century interannual and secular variability. Time series of mean sea level hSL(t) and total recorded M2 vector aTT(t) are extracted from the Honolulu 1905–2000 and Hilo 1947–2000 (Hawaii) tide records. Internal tide parameters are derived from the intertidal continuum surrounding the M2 frequency line and from a Cartesian display of aTT(t), yielding aST = 16.6 and 22.1 cm, aIT = 1.8 and 1.0 cm for surface and internal tides at Honolulu and Hilo, respectively. The proposed model aTT(t) = aST + aIT cosθIT(t) is of a phase-modulated internal tide generated by the surface tide at some remote point and traveling to the tide gauge with velocity modulated by the underlying variable density structure. Mean sea level hSL(t) [a surrogate for the density structure and hence for θIT(t)] is coherent with aIT(t) within the decadal band 0.2–0.5 cycles per year. For both the decadal band and the century drift the recorded M2 amplitude is high when sea level is high, according to δaTT = O(0.1δhSL). The authors attribute the recorded secular increase in the Honolulu M2 amplitude from aTT = 16.1 to 16.9 cm between 1915 and 2000 to a 28° rotation of the internal tide vector in response to ocean warming.
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  • 187
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 1822-1840, doi:10.1175/JPO2932.1.
    Description: An isopycnal, two-layer, idealized model for a convective basin is proposed, consisting of a convecting, interior region and a surrounding boundary current (buoyancy and wind-driven). Parameterized eddy fluxes govern the exchange between the two. To balance the interior buoyancy loss, the boundary current becomes denser as it flows around the basin. Geostrophy imposes that this densification be accompanied by sinking in the boundary current and hence by an overturning circulation. The poleward heat transport, associated with convection in the basin, can thus be viewed as a result of both an overturning and a horizontal circulation. When adapted to the Labrador Sea, the model is able to reproduce the bulk features of the mean state, the seasonal cycle, and even the shutdown of convection from 1969 to 1972. According to the model, only 40% of the poleward heat (buoyancy) transport of the Labrador Sea is associated with the overturning circulation. An exact solution is presented for the linearized equations when changes in the boundary current are small. Numerical solutions are calculated for variations in the amount of convection and for changes in the remotely forced circulation around the basin. These results highlight how the overturning circulation is not simply related to the amount of dense water formed. A speeding up of the circulation around the basin due to wind forcing, for example, will decrease the intensity of the overturning circulation while the dense water formation remains unvaried. In general, it is shown that the fraction of poleward buoyancy (or heat) transport carried by the overturning circulation is not an intrinsic property of the basin but can vary as a result of a number of factors.
    Description: This work was supported by NSF OCE 02-40978 and by the Climate Institute at the Woods Hole Oceanographic Institution (WHOI).
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  • 188
    facet.materialart.
    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 1241-1264, doi:10.1175/JPO2907.1.
    Description: Subsurface float and surface drifter observations illustrate the structure, evolution, and eventual demise of 10 North Brazil Current (NBC) rings as they approached and collided with the Lesser Antilles in the western tropical Atlantic Ocean. Upon encountering the shoaling topography east of the Lesser Antilles, most of the rings were deflected abruptly northward and several were observed to completely engulf the island of Barbados. The near-surface and subthermocline layers of two rings were observed to cleave or separate upon encountering shoaling bathymetry between Tobago and Barbados, with the resulting portions each retaining an independent and coherent ringlike vortical circulation. Surface drifters and shallow (250 m) subsurface floats that looped within NBC rings were more likely to enter the Caribbean through the passages of the Lesser Antilles than were deeper (500 or 900 m) floats, indicating that the regional bathymetry preferentially inhibits transport of intermediate-depth ring components. No evidence was found for the wholesale passage of rings through the island chain.
    Description: Funding was provided by National Science Foundation Grants OCE 97-29765 and OCE 01-36477.
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  • 189
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 2296-2311, doi:10.1175/JPO2959.1.
    Description: The subtidal salt balance and the mechanisms driving the downgradient salt flux in the Hudson River estuary are investigated using measurements from a cross-channel mooring array of current meters, temperature and conductivity sensors, and cross-channel and along-estuary shipboard surveys obtained during the spring of 2002. Steady (subtidal) vertical shear dispersion, resulting from the estuarine exchange flow, was the dominant mechanism driving the downgradient salt flux, and varied by over an order of magnitude over the spring–neap cycle, with maximum values during neap tides and minimum values during spring tides. Corresponding longitudinal dispersion rates were as big as 2500 m2 s−1 during neap tides. The salinity intrusion was not in a steady balance during the study period. During spring tides, the oceanward advective salt flux resulting from the net outflow balanced the time rate of change of salt content landward of the study site, and salt was flushed out of the estuary. During neap tides, the landward steady shear dispersion salt flux exceeded the oceanward advective salt flux, and salt entered the estuary. Factor-of-4 variations in the salt content occurred at the spring–neap time scale and at the time scale of variations in the net outflow. On average, the salt flux resulting from tidal correlations between currents and salinity (tidal oscillatory salt flux) was an order of magnitude smaller than that resulting from steady shear dispersion. During neap tides, this flux was minimal (or slightly countergradient) and was due to correlations between tidal currents and vertical excursions of the halocline. During spring tides, the tidal oscillatory salt flux was driven primarily by oscillatory shear dispersion, with an associated longitudinal dispersion rate of about 130 m2 s−1.
    Description: This work was supported by National Science Foundation Grant OCE00-95972 and Hudson River Foundation Grant 005/03A. Author Lerczak received partial support from the Penzance Endowed Fund in Support of Assistant Scientists.
    Keywords: Ice shelves ; Dynamics ; Antarctica
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  • 190
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 1420-1429, doi:10.1175/JPO2914.1.
    Description: The gravitational potential energy balance of the thermal circulation in a simple rectangular model basin is diagnosed from numerical experiments based on a mass-conserving oceanic general circulation model. The vertical mixing coefficient is assumed to be a given constant. The model ocean is heated/cooled from the upper surface or bottom, and the equation of state is linear or nonlinear. Although the circulation patterns obtained from these cases look rather similar, the energetics of the circulation may be very different. For cases of differential heating from the bottom with a nonlinear equation of state, the circulation is driven by mechanical energy generated by heating from the bottom. On the other hand, circulation for three other cases is driven by external mechanical energy, which is implicitly provided by tidal dissipation and wind stress. The major balance of gravitational energy in this model ocean is between the source of energy due to vertical mixing and the conversion from kinetic energy at low latitudes and the sink of energy due to convection adjustment and conversion to kinetic energy at high latitudes.
    Description: RXH and XZJ were supported by the National Science Foundation through Grant OCE0094807 to the Woods Hole Oceanographic Institution and the Van Alan Clark Chair of the Woods Hole Oceanographic Institution.
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  • 191
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 629-635, doi:10.1175/JPO2890.1.
    Description: Previous field observations indicate that the directional spread of swell-frequency (nominally 0.1 Hz) surface gravity waves increases during shoreward propagation across the surf zone. This directional broadening contrasts with the narrowing observed seaward of the surf zone and predicted by Snell’s law for bathymetric refraction. Field-observed broadening was predicted by a new model for refraction of swell by lower-frequency (nominally 0.01 Hz) current and elevation fluctuations. The observations and the model suggest that refraction by the cross-shore currents of energetic shear waves contributed substantially to the observed broadening.
    Description: Funding was provided by the Office of Naval Research, the National Science Foundation, and the National Ocean Partnership Program.
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  • 192
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 1305-1316, doi:10.1175/JPO2909.1.
    Description: Observations of the buoyant coastal current that flows southward from Chesapeake Bay are used to describe how the thickness, width, and propagation speed vary in response to changes in the along-shelf wind stress. Three basic regimes were observed depending on the strength of the wind. For weak wind stresses (from −0.02 to 0.02 Pa), the buoyant coastal current was relatively thin, the front slope was not steep, and the width was variable (1–20 km). For moderate downwelling (southward) wind stresses (0.02–0.07 Pa), wind-driven cross-shelf advection steepened the front, causing the plume to narrow and thicken. For stronger downwelling wind stresses (greater than 0.07 Pa), vertical mixing dominated, bulk Richardson numbers were approximately 0.25, isopycnals were nearly vertical, and the plume front widened but the plume width did not change. Plume thickness and width were normalized by the theoretical plume scales in the absence of wind forcing. Normalized plume thickness increased linearly from 1 to 2 as downwelling wind stresses increased from 0 to 0.2 Pa. Normalized plume widths were approximately 1 for downwelling wind stresses from 0.02 to 0.2 Pa. The observed along-shelf propagation speed of the plume was roughly equal to the sum of the theoretical propagation speed and the wind-driven along-shelf flow.
    Description: This work was funded by the National Science Foundation under Grants OCE-0095059, OCE-0220773, OCE-92-21614, and OCE-96-33013.
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  • 193
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    Unknown
    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2006. 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 36 (2006): 2185-2198, doi:10.1175/JPO2967.1.
    Description: The time-dependent response of an ocean basin to the imposition of cooling (or heating) is examined in the context of a quasigeostrophic, two-layer model on the beta plane. The focus is on the structure and magnitude of the vertical motion and its response to both a switch-on forcing and a periodic forcing. The model employed is a time-dependent version of an earlier model used to discuss the intensification of sinking in the region of the western boundary current. The height of the interface of the two-layer model serves as an analog of temperature, and the vertical velocity at the interface consists of a cross-isopycnal velocity modeled in terms of a relaxation to a prescribed interface height, an adiabatic representation of eddy thickness fluxes parameterized as lateral diffusion of thickness, and the local vertical motion of the interface itself. The presence of time dependence adds additional dynamical features to the problem, in particular the emergence of low-frequency, weakly damped Rossby basin modes. If the buoyancy forcing is zonally uniform the basin responds to a switch-on of the forcing by coming into steady-state equilibrium after the passage of a single baroclinic Rossby wave. If the forcing is nonuniform in the zonal direction, a sequence of Rossby basin modes is excited and their decay is required before the basin achieves a steady state. For reasonable parameter values the boundary layers, in which both horizontal and vertical circulations are closed, are quasi-steady and respond to the instantaneous state of the interior. As in the steady problem the flow is sensitive to small nonquasigeostrophic mass fluxes across the perimeter of the basin. These fluxes generally excite basin modes as well. The basin modes will also be weakly excited if the beta-plane approximation is relaxed. The response to periodic forcing is also examined, and the sensitivity of the response to the structure of the forcing is similar to the switch-on problem.
    Description: This research was supported in part by NSF Grant OCE-9901654,
    Keywords: Vertical motion ; Ocean dynamics ; Buoyancy ; Ocean models
    Repository Name: Woods Hole Open Access Server
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  • 194
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    American Meteorological Society
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. 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 35 (2005): 374-387, doi:10.1175/JPO-2692.1.
    Description: Observations at the mouth of the Fraser River (British Columbia, Canada) indicate an abrupt frontal transition between unstratified river outflow and a highly stratified river plume with differences in salinity greater than 25 psu across a few meters in the vertical direction and several hundred meters in the horizontal direction. The front roughly follows a natural break in the bathymetry, crossing the channel at an angle of approximately 45°, and is essentially stationary for a period of approximately 3.5 h centered on the low tide following the larger of two daily ebbs. The location of the front is coincident with observations of significantly supercritical internal Froude numbers at the front, based on velocities in the along-flow direction. This observation contradicts the one-dimensional theory, which indicates that the Froude number should be 1. However, because the front is oriented obliquely to the outflow, a coordinate system can be selected that is normal to the front and for which a critical Froude number of 1 is obtained. This indicates that a Froude angle, similar in application to a Mach angle for transonic flows, can be used to determine critical conditions when the front is oblique to the principal flow direction.
    Description: This work was performed as a part of D. MacDonald’s Ph.D. thesis, and was funded by Office of Naval Research Grants N000-14-97-10134 and N000-14-97- 10566, National Science Foundation Grant OCE- 9906787, a National Science Foundation graduate fellowship, and support from the WHOI Academic Programs Office.
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  • 195
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. 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 41 (2011): 1160–1181, doi:10.1175/2011JPO4547.1.
    Description: Tropical instability waves are triggered by instabilities of the equatorial current systems, and their sea level signal, with peak amplitude near 5°N, is one of the most prominent features of the dynamic topography of the tropics. Cross-spectral analysis of satellite altimetry observations shows that there is sea level variability in the Pacific Ocean as far north as Hawaii (i.e., 20°N) that is coherent with the sea level variability near 5°N associated with tropical instability waves. Within the uncertainty of the analysis, this off-equatorial variability obeys the dispersion relation for nondivergent, barotropic Rossby waves over a fairly broad range of periods (26–38 days) and zonal wavelengths (9°–23° of longitude) that are associated with tropical instability waves. The dispersion relation and observed wave properties further suggest that the waves are carrying energy away from the instabilities toward the North Pacific subtropical gyre, which, together with the observed coherence of the sea level signal of the barotropic waves with that of the tropical instability waves, suggests that the barotropic Rossby waves are being radiated from the tropical instability waves. The poleward transport of kinetic energy and westward momentum by these barotropic Rossby waves may influence the circulation in the subtropics.
    Description: Funding for this research came from WHOI’s TropicalResearch Initiative, the Charles D. Hollister Fund for Assistant Scientist Support, the John E. and Anne W. Sawyer Endowed Fund in Special Support of Scientific Staff, and Grant OCE-0845150 from the National Science Foundation.
    Keywords: Barotropic flows ; Rossby waves ; Tropics ; Pacific Ocean ; Instability ; Waves, atmospheric
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  • 196
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. 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 41 (2011): 1874–1893, doi:10.1175/2011JPO4604.1.
    Description: A two-dimensional cross-shelf model of the New England continental shelf and slope is used to investigate the mean cross-shelf and vertical circulation at the shelf break and their seasonal variation. The model temperature and salinity fields are nudged toward climatology. Annual and seasonal mean wind stresses are applied on the surface in separate equilibrium simulations. The along-shelf pressure gradient force associated with the along-shelf sea level tilt is tuned to match the modeled and observed depth-averaged along-shelf velocity. Steady-state model solutions show strong seasonal variation in along-shelf and cross-shelf velocity, with the strongest along-shelf jet and interior onshore flow in winter, consistent with observations. Along-shelf sea level tilt associated with the tuned along-shelf pressure gradient increases shoreward because of decreasing water depth. The along-shelf sea level tilt varies seasonally with the wind and is the strongest in winter and weakest in summer. A persistent upwelling is generated at the shelf break with a maximum strength of 2 m day−1 at 50-m depth in winter. The modeled shelfbreak upwelling differs from the traditional view in that most of the upwelled water is from the upper continental slope instead of from the shelf in the form of a detached bottom boundary layer.
    Description: WGZ was supported by the Woods Hole Oceanographic Institution postdoctoral scholarship program. GGGandDJMwere supported byONRGrant N-00014- 06-1-0739.
    Keywords: Ocean circulation ; North Atlantic Ocean
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  • 197
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2011. 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 41 (2011): 2168–2186, doi:10.1175/JPO-D-11-08.1.
    Description: This paper studies the interaction of an Antarctic Circumpolar Current (ACC)–like wind-driven channel flow with a continental slope and a flat-bottomed bay-shaped shelf near the channel’s southern boundary. Interaction between the model ACC and the topography in the second layer induces local changes of the potential vorticity (PV) flux, which further causes the formation of a first-layer PV front near the base of the topography. Located between the ACC and the first-layer slope, the newly formed PV front is constantly perturbed by the ACC and in turn forces the first-layer slope with its own variability in an intermittent but persistent way. The volume transport of the slope water across the first-layer slope edge is mostly directly driven by eddies and meanders of the new front, and its magnitude is similar to the maximum Ekman transport in the channel. Near the bay’s opening, the effect of the topographic waves, excited by offshore variability, dominates the cross-isobath exchange and induces a mean clockwise shelf circulation. The waves’ propagation is only toward the west and tends to be blocked by the bay’s western boundary in the narrow-shelf region. The ensuing wave–coast interaction amplifies the wave amplitude and the cross-shelf transport. Because the interaction only occurs near the western boundary, the shelf water in the west of the bay is more readily carried offshore than that in the east and the mean shelf circulation is also intensified along the bay’s western boundary.
    Description: Y. Zhang acknowledges the support of the MIT-WHOI Joint Program in Physical Oceanography and NSF OCE-9901654 and OCE- 0451086. J. Pedlosky acknowledges the support of NSF OCE-9901654 and OCE-0451086.
    Keywords: Baroclinic flows ; Eddies ; Fronts ; Mass fluxes/transport ; Mesoscale processes ; Topographic effects
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  • 198
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. 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 25 (2012): 343–349, doi:10.1175/JCLI-D-11-00059.1.
    Description: The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.
    Description: KBK gratefully acknowledges the J. Lamar Worzel Assistant Scientist Fund. GCJ is supported by NOAA’s Office of Oceanic and Atmospheric Research. RM gratefully acknowledges the generous support and hospitality of the Divecha Centre for Climate Change and CAOS at IISc, Bangalore, and partial support by NASA PO grants.
    Description: 2012-07-01
    Keywords: Tropics ; Ocean circulation ; Ocean dynamics ; Climate models ; Coupled models ; Ocean models
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  • 199
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. 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 25 (2012): 1096–1115, doi:10.1175/2011JCLI4228.1.
    Description: Ventilation, including subduction and obduction, for the global oceans was examined using Simple Ocean Data Assimilation (SODA) outputs. The global subduction rate averaged over the period from 1959 to 2006 is estimated at 505.8 Sv (1 Sv ≡ 106 m3 s−1), while the corresponding global obduction rate is estimated at 482.1 Sv. The annual subduction/obduction rates vary greatly on the interannual and decadal time scales. The global subduction rate is estimated to have increased 7.6% over the past 50 years, while the obduction rate is estimated to have increased 9.8%. Such trends may be insignificant because errors associated with the data generated by ocean data assimilation could be as large as 10%. However, a major physical mechanism that induced these trends is primarily linked to changes in the Southern Ocean. While the Southern Ocean plays a key role in global subduction and obduction rates and their variability, both the Southern Ocean and equatorial regions are critically important sites of water mass formation/erosion.
    Description: This work was supported by the Key State Basic Research Program of China under Grant 2012CB417401, the National Natural Science Foundation of China (Grants 40906007, 40890152), and the Open Foundation of Physical Oceanography Laboratory, OUC, under Grant 200902.
    Description: 2012-08-15
    Keywords: Decadal variability ; Southern Ocean ; Trends ; Water masses ; Convergence ; Mixing
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  • 200
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2012. 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 42 (2012): 659–668, doi:10.1175/JPO-D-11-0125.1.
    Description: Ice-tethered profiler (ITP) measurements from the Arctic Ocean’s Canada Basin indicate an ocean surface layer beneath sea ice with significant horizontal density structure on scales of hundreds of kilometers to the order 1 km submesoscale. The observed horizontal gradients in density are dynamically important in that they are associated with restratification of the surface ocean when dense water flows under light water. Such restratification is prevalent in wintertime and competes with convective mixing upon buoyancy forcing (e.g., ice growth and brine rejection) and shear-driven mixing when the ice moves relative to the ocean. Frontal structure and estimates of the balanced Richardson number point to the likelihood of dynamical restratification by isopycnal tilt and submesoscale baroclinic instability. Based on the evidence here, it is likely that submesoscale processes play an important role in setting surface-layer properties and lateral density variability in the Arctic Ocean.
    Description: Funding was provided by the National Science Foundation Office of Polar Programs Arctic Sciences Section under Awards ARC-0519899, ARC-0856479, and ARC-0806306. Support was also provided by the Woods Hole Oceanographic Institution Arctic Research Initiative.
    Description: 2012-10-01
    Keywords: Arctic ; Ocean dynamics
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