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  • Ocean circulation  (123)
  • Ocean models
  • American Meteorological Society  (99)
  • Woods Hole Oceanographic Institution  (44)
  • John Wiley & Sons  (7)
  • Annual Reviews
  • 1
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    Assimilating Along-Track Altimetric Observations through Local Hydrostatic Adjustment in a Global Ocean Variational Assimilation System (2012)
    American Meteorological Society
    Details
    Publikationsdatum: 2017-04-03
    Beschreibung: A global ocean three-dimensional variational data assimilation system was developed with the aim of assimilating along-track sea level anomaly observations, along with in situ observations from bathythermographs and conventional sea stations. All the available altimetric data within the period October 1992–January 2006 were used in this study. The sea level corrections were covariated with vertical profiles of temperature and salinity according to the bivariate definition of the background-error vertical covariances. Sea level anomaly observational error variance was carefully defined as a sum of instrumental, representativeness, observation operator, and mean dynamic topography error variances. The mean dynamic topography was computed from the model long-term mean sea surface height and adjusted through an optimal interpolation scheme to account for observation minus first-guess biases. Results show that the assimilation of sea level anomaly observations improves the model sea surface height skill scores as well as the subsurface temperature and salinity fields. Furthermore, the estimate of the tropical and subtropical surface circulation is clearly improved after assimilating altimetric data. Nonnegligible impacts of the mean dynamic topography used have also been found: compared to a gravimeter-based mean dynamic topography the use of the mean dynamic topography discussed in this paper improves both the consistency with sea level anomaly observations and the verification skill scores of temperature and salinity in the tropical regions. Furthermore, the use of a mean dynamic topography computed from the model long-term sea surface height mean without observation adjustments results in worsened verification skill scores and highlights the benefits of the current approach for deriving the mean dynamic topography.
    Beschreibung: European Commission WP4 Fondazione Cassa di Risparmio di Bologna Cnes
    Beschreibung: Published
    Beschreibung: 738-754
    Beschreibung: 3.7. Dinamica del clima e dell'oceano
    Beschreibung: 4.6. Oceanografia operativa per la valutazione dei rischi in aree marine
    Beschreibung: 5.4. Banche dati di geomagnetismo, aeronomia, clima e ambiente
    Beschreibung: JCR Journal
    Beschreibung: partially_open
    Schlagwort(e): Data assimilation ; Satellite observations ; Ocean models ; Sea level ; In situ observations ; Variational analysis ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling ; 03. Hydrosphere::03.01. General::03.01.03. Global climate models ; 03. Hydrosphere::03.01. General::03.01.04. Ocean data assimilation and reanalysis
    Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Seasonal variations in the circulation over the Middle Atlantic Bight continental shelf (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1486–1500, doi:10.1175/2007JPO3767.1.
    Beschreibung: Fits of an annual harmonic to depth-average along-shelf current time series longer than 200 days from 27 sites over the Middle Atlantic Bight (MAB) continental shelf have amplitudes of a few centimeters per second. These seasonal variations are forced by seasonal variations in the wind stress and the cross-shelf density gradient. The component of wind stress that drives the along-shelf flow over most of the MAB mid- and outer shelf is oriented northeast–southwest, perpendicular to the major axis of the seasonal variation in the wind stress. Consequently, there is not a significant seasonal variation in the wind-driven along-shelf flow, except over the southern MAB shelf and the inner shelf of New England where the wind stress components forcing the along-shelf flow are north–south and east–west, respectively. The seasonal variation in the residual along-shelf flow, after removing the wind-driven component, has an amplitude of a few centimeters per second with maximum southwestward flow in spring onshore of the 60-m isobath and autumn offshore of the 60-m isobath. The spring maximum onshore of the 60-m isobath is consistent with the maximum river discharges in spring enhancing cross-shelf salinity gradients. The autumn maximum offshore of the 60-m isobath and a steady phase increase with water depth offshore of Cape Cod are both consistent with the seasonal variation in the cross-shelf temperature gradient associated with the development and destruction of a near-bottom pool of cold water over the mid and outer shelf (“cold pool”) due to seasonal variations in surface heat flux and wind stress.
    Beschreibung: This research was funded by the Ocean Sciences Division of the National Science Foundation under Grants OCE-820773, OCE-841292, and OCE- 848961.
    Schlagwort(e): Seasonal variability ; Ocean circulation ; Continental shelf ; Wind stress ; Density currents
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 3
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    A laboratory model of vertical ocean circulation driven by mixing (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1091-1106, doi:10.1175/2007JPO3805.1.
    Beschreibung: A model of deep ocean circulation driven by turbulent mixing is produced in a long, rectangular laboratory tank. The salinity difference is substituted for the thermal difference between tropical and polar regions. Freshwater gently flows in at the top of one end, dense water enters at the same rate at the top of the other end, and an overflow in the middle removes the same amount of surface water as is pumped in. Mixing is provided by a rod extending from top to bottom of the tank and traveling back and forth at constant speed with Reynolds numbers 〉500. A stratified upper layer (“thermocline”) deepens from the mixing and spreads across the entire tank. Simultaneously, a turbulent plume (“deep ocean overflow”) from a dense-water source descends through the layer and supplies bottom water, which spreads over the entire tank floor and rises into the upper layer to arrest the upper-layer deepening. Data are taken over a wide range of parameters and compared to scaling theory, energetic considerations, and simple models of turbulently mixed fluid. There is approximate agreement with a simple theory for Reynolds number 〉1000 in experiments with a tank depth less than the thermocline depth. A simple argument shows that mixing and plume potential energy flux rates are equal in magnitude, and it is suggested that the same is approximately true for the ocean.
    Beschreibung: The research was supported by the Ocean Climate Change Institute of Woods Hole Oceanographic Institution.
    Schlagwort(e): Ocean circulation ; Mixing ; In situ observations ; Vertical motion
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 4
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    Can paleoceanographic tracers constrain meridional circulation rates? (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 394-407, doi:10.1175/jpo3018.1.
    Beschreibung: The ability of paleoceanographic tracers to constrain rates of transport is examined using an inverse method to combine idealized observations with a geostrophic model. Considered are the spatial distribution, accuracy, and types of tracers required to constrain changes in meridional transport within an idealized single-hemisphere basin. Measurements of density and radioactive tracers each act to constrain rates of transport. Conservative tracers, while not of themselves able to inform regarding rates of transport, improve constraints when coupled with density or radioactive observations. It is found that the tracer data would require an accuracy one order of magnitude better than is presently available for paleo-observations to conclusively rule out factor-of-2 changes in meridional transport, even when assumed available over the entire model domain. When data are available only at the margins and bottom of the model, radiocarbon is unable to constrain transport while density remains effective only when a reference velocity level is assumed. The difficulty in constraining the circulation in this idealized model indicates that placing firm bounds on past meridional transport rates will prove challenging.
    Beschreibung: The first author is supported by the NOAA Postdoctoral Program in Climate and Global Change and GG by the National Ocean Partnership Program (ECCO). Author OM acknowledges support from the National Science Foundation.
    Schlagwort(e): Tracers ; Transport ; Paleoclimatology ; Ocean models
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 5
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    A comparison of methods for estimating Reynolds stress from ADCP measurements in wavy environments (2012)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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 Atmospheric and Oceanic Technology 28 (2011): 1539–1553, doi:10.1175/JTECH-D-11-00001.1.
    Beschreibung: Turbulent Reynolds stresses are now routinely estimated from acoustic Doppler current profiler (ADCP) measurements in estuaries and tidal channels using the variance method, yet biases due to surface gravity waves limit its use in the coastal ocean. Recent modifications to this method, including spatially filtering velocities to isolate the turbulence from wave velocities and fitting a cospectral model to the below-wave band cospectra, have been used to remove this bias. Individually, each modification performed well for the published test datasets, but a comparative analysis over the range of conditions in the coastal ocean has not yet been performed. This work uses ADCP velocity measurements from five previously published coastal ocean and estuarine datasets, which span a range of wave and current conditions as well as instrument configurations, to directly compare methods for estimating stresses in the presence of waves. The computed stresses from each were compared to bottom stress estimates from a quadratic drag law and, where available, estimates of wind stress. These comparisons, along with an analysis of the cospectra, indicated that spectral fitting performs well when the wave climate is wide-banded and/or multidirectional as well as when instrument noise is high. In contrast, spatial filtering performs better when waves are narrow-banded, low frequency, and when wave orbital velocities are strong relative to currents. However, as spatial filtering uses vertically separated velocity bins to remove the wave bias, spectral fitting is able to resolve stresses over a larger fraction of the water column.
    Beschreibung: J. Rosman acknowledges funding from the National Science Foundation (OCE-1061108).
    Schlagwort(e): Coastal flows ; Momentum ; Ocean circulation ; Waves, oceanic ; In situ observations ; Instrumentation/sensors
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 6
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    Variability of the Atlantic meridional overturning circulation in CCSM4 (2012)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 5153–5172, doi:10.1175/JCLI-D-11-00463.1.
    Beschreibung: Atlantic meridional overturning circulation (AMOC) variability is documented in the Community Climate System Model, version 4 (CCSM4) preindustrial control simulation that uses nominal 1° horizontal resolution in all its components. AMOC shows a broad spectrum of low-frequency variability covering the 50–200-yr range, contrasting sharply with the multidecadal variability seen in the T85 × 1 resolution CCSM3 present-day control simulation. Furthermore, the amplitude of variability is much reduced in CCSM4 compared to that of CCSM3. Similarities as well as differences in AMOC variability mechanisms between CCSM3 and CCSM4 are discussed. As in CCSM3, the CCSM4 AMOC variability is primarily driven by the positive density anomalies at the Labrador Sea (LS) deep-water formation site, peaking 2 yr prior to an AMOC maximum. All processes, including parameterized mesoscale and submesoscale eddies, play a role in the creation of salinity anomalies that dominate these density anomalies. High Nordic Sea densities do not necessarily lead to increased overflow transports because the overflow physics is governed by source and interior region density differences. Increased overflow transports do not lead to a higher AMOC either but instead appear to be a precursor to lower AMOC transports through enhanced stratification in LS. This has important implications for decadal prediction studies. The North Atlantic Oscillation (NAO) is significantly correlated with the positive boundary layer depth and density anomalies prior to an AMOC maximum. This suggests a role for NAO through setting the surface flux anomalies in LS and affecting the subpolar gyre circulation strength.
    Beschreibung: The CCSM project is supported by NSF and the Office of Science (BER) of the U.S. Department of Energy. SGY and YOK were supported by the NOAA Climate Program Office under Climate Variability and Predictability Program Grants NA09OAR4310163 and NA10OAR4310202, respectively.
    Beschreibung: 2013-02-01
    Schlagwort(e): Meridional overturning circulation ; Coupled models ; Ocean models ; Oceanic variability
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 7
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    On eddy viscosity, energy cascades, and the horizontal resolution of gridded satellite altimeter products (2013)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2013-08-01
    Schlagwort(e): Eddies ; Nonlinear dynamics ; Ocean dynamics ; Satellite observations ; Ocean models
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 8
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    Wind-driven cross-equatorial flow in the Indian Ocean (2013)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2013-06-01
    Schlagwort(e): Indian Ocean ; Subtropics ; Currents ; Ocean circulation ; Transport ; Wind stress
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 9
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    Strong sea surface cooling in the eastern equatorial Pacific and implications for Galápagos Penguin conservation (2015)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 42 (2015): 6432–6437, doi:10.1002/2015GL064456.
    Beschreibung: The Galápagos is a flourishing yet fragile ecosystem whose health is particularly sensitive to regional and global climate variations. The distribution of several species, including the Galápagos Penguin, is intimately tied to upwelling of cold, nutrient-rich water along the western shores of the archipelago. Here we show, using reliable, high-resolution sea surface temperature observations, that the Galápagos cold pool has been intensifying and expanding northward since 1982. The linear cooling trend of 0.8°C/33 yr is likely the result of long-term changes in equatorial ocean circulation previously identified. Moreover, the northward expansion of the cold pool is dynamically consistent with a slackening of the cross-equatorial component of the regional trade winds—leading to an equatorward shift of the mean position of the Equatorial Undercurrent. The implied change in strength and distribution of upwelling has important implications for ongoing and future conservation measures in the Galápagos.
    Beschreibung: K.B.K. acknowledges support from the Alfred P. Sloan Foundation, the James E. and Barbara V. Moltz Fellowship administered by the Woods Hole Oceanographic Institution (WHOI) Ocean and Climate Change Institute (OCCI), and the National Science Foundation (NSF) Physical Oceanography program (grant OCE–1233282). S.J. acknowledges support from WHOI. C.W.B. was supported by the NOAA Center for Satellite Applications and Research.
    Beschreibung: 2016-02-06
    Schlagwort(e): Upwelling ; Conservation ; Penguins ; Galapagos ; Ocean circulation ; Climate
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 10
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    Robust warming pattern of global subtropical oceans and its mechanism (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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).
    Beschreibung: 2016-05-01
    Schlagwort(e): Circulation/ Dynamics ; Ocean circulation ; Physical Meteorology and Climatology ; Climate change
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 11
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    Evolution of the freshwater coastal current at the southern tip of Greenland (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: Funding for this project was provided by the National Science Foundation under Grant OCE-1259618.
    Beschreibung: 2019-03-11
    Schlagwort(e): Boundary currents ; Coastal flows ; Instability ; Ocean circulation ; Potential vorticity ; Transport
    Repository-Name: Woods Hole Open Access Server
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  • 12
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    Ocean response to a hurricane, part II : data tabulations and numerical modeling (2006)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-25
    Beschreibung: Field observations of the ocean's forced stage response to three hurricanes, Norbert (1984), Josephine (1984) and Gloria (1985), are analyzed and presented in a storm-centered coordinate system. All three hurricanes had a non-dimensional speed of O(1) and produced a strongly rightward biased response of the ocean surface mixed layer (SML) transport and current. The maximum layer-averaged SML currents varried from 0.8 m S-1 in response to Josephine, which was a fairly weak hurricane, to 1.7 m S.l in response to Gloria, which was much stronger. In these two cases the current amplitude is set primarly by the strength of the wind stress and its efficiency of coupling with the SML current, and the depth of vertical mixing of the SML. The Norbert case (SML Burger number ≈ 1/2) was also affected by significant pressure-coupling with the thermocline that caused appreciable upwellng by inertial pumping and strong thermocline-depth currents, up to 0.3 m S-l, under the trailing edge of Norbert. The observed SML current has a vertical shear in the direction of the local wind of up to 0.01 S-l. This vertical shear causes the surface current to be larger than the layer-averaged SML current described above by typically 0.2 m S.l.
    Beschreibung: Funding was provided by the Office of Naval Research under grant No. N00014-89-J-I053.
    Schlagwort(e): Ocean models ; Wind-driven currents ; Aircraft measurements
    Repository-Name: Woods Hole Open Access Server
    Materialart: Technical Report
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  • 13
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    The upper-oceanic response to overflows : a mechanism for the Azores Current (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Schlagwort(e): North Atlantic Ocean ; Mediterranean region ; Ocean models ; Mass fluxes/transport ; Diapycnal mixing
    Repository-Name: Woods Hole Open Access Server
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  • 14
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    Observations and a model of the mean circulation over the Middle Atlantic Bight continental shelf (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: This research was funded by Ocean Sciences Division of the National Science Foundation under Grants OCE-820773, OCE-841292, and OCE-848961.
    Schlagwort(e): Ocean models ; Ocean circulation ; Continental shelf ; Currents ; In situ observations
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  • 15
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    Ocean eddy dynamics in a coupled ocean-atmosphere model (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Schlagwort(e): Ocean dynamics ; Ocean models ; Eddies ; Jets ; Coupled models
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  • 16
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    Rossby wave instability and apparent phase speeds in large ocean basins (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Schlagwort(e): Rossby waves ; Ocean models ; Barotropic flows ; Baroclinic flows
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  • 17
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    Time-dependent response to cooling in a beta-plane basin (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: This research was supported in part by NSF Grant OCE-9901654,
    Schlagwort(e): Vertical motion ; Ocean dynamics ; Buoyancy ; Ocean models
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  • 18
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    Climatological mean circulation at the New England shelf break (2011)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: WGZ was supported by the Woods Hole Oceanographic Institution postdoctoral scholarship program. GGGandDJMwere supported byONRGrant N-00014- 06-1-0739.
    Schlagwort(e): Ocean circulation ; North Atlantic Ocean
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  • 19
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    An equatorial ocean bottleneck in global climate models (2012)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 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.
    Beschreibung: 2012-07-01
    Schlagwort(e): Tropics ; Ocean circulation ; Ocean dynamics ; Climate models ; Coupled models ; Ocean models
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  • 20
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    On the response of a buoyant plume to downwelling-favorable wind stress (2012)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1083–1098, doi:10.1175/JPO-D-11-015.1.
    Beschreibung: Here, the response of a coastally trapped buoyant plume to downwelling-favorable wind forcing is explored using a simplified two-dimensional numerical model and a prognostic theory for the resulting width, depth, and density anomaly and along-shelf transport of the plume. Consistent with the numerical simulations, the analytical model shows that the wind causes mixing of the plume water and that the forced cross-shelf circulation can also generate significant deepening and surface narrowing, as well as increased along-shelf transport. The response is due to a combination of the purely advective process that leads to the steepening of the isopycnals and the entrainment of ambient water into the plume. The advective component depends on the initial plume geometry: plumes that have a large fraction of their total width in contact with the bottom (“bottom trapped”) suffer relatively small depth and width changes compared to plumes that have a large fraction of their total width detached from the bottom (“surface trapped”). Key theoretical parameters are Wγ/Wα, the ratio of the width of the plume detached from the bottom to the width of the plume in contact with it, and the ratio of the wind-generated mixed layer δe to the initial plume depth hp, which determines the amount of water initially entrained into the plume. The model results also show that the cross-shelf circulation can be strongly influenced by the wind-driven response in combination with the geostrophic shear of the plume. The continuous entrainment into the plume, as well as transient events, is also discussed.
    Beschreibung: This work has been supported by FONDECYT Grant 1070501. S. Lentz received support by theNational Science Foundation GrantOCE-0751554. C. Moffat had additional support from the National Science Foundation Office of Polar Programs through U.S. Southern Ocean GLOBEC Grants OPP 99-10092 and 06- 23223.
    Beschreibung: 2013-01-01
    Schlagwort(e): Baroclinic flows ; Boundary currents ; Coastal flows ; Upwelling/downwelling ; Wind ; Ocean models
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  • 21
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    ENSO’s impact on the gap wind regions of the eastern tropical Pacific Ocean (2012)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 3549–3565, doi:10.1175/JCLI-D-11-00320.1.
    Beschreibung: The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niño events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not.
    Beschreibung: This research was supported by grants from the NOAA office of Global Programs and the NSF Climate and Global Dynamics Division.
    Beschreibung: 2012-11-15
    Schlagwort(e): North Pacific Ocean ; Atmosphere-ocean interaction ; ENSO ; Thermocline circulation ; Waves, oceanic ; Ocean models
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  • 22
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    Abrupt changes in deep Atlantic circulation during the transition to full glacial conditions (2013)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 28 (2013): 253–262, doi:10.1002/palo.20025.
    Beschreibung: Six Ocean Drilling Program (ODP) sites, in the Northwest Atlantic have been used to investigate kinematic and chemical changes in the “Western Boundary Undercurrent” (WBUC) during the development of full glacial conditions across the Marine Isotope Stage 5a/4 boundary (~70,000 years ago). Sortable silt mean grain size inline image measurements are employed to examine changes in near bottom flow speeds, together with carbon isotopes measured in benthic foraminifera and % planktic foraminiferal fragmentation as proxies for changes in water-mass chemistry. A depth transect of cores, spanning 1.8–4.6 km depth, allows changes in both the strength and depth of the WBUC to be constrained across millennial scale events. inline image measurements reveal that the flow speed structure of the WBUC during warm intervals (“interstadials”) was comparable to modern (Holocene) conditions. However, significant differences are observed during cold intervals, with higher relative flow speeds inferred for the shallow component of the WBUC (~2 km depth) during all cold “stadial” intervals (including Heinrich Stadial 6), and a substantial weakening of the deep component (~3–4 km) during full glacial conditions. Our results therefore reveal that the onset of full glacial conditions was associated with a regime shift to a shallower mode of circulation (involving Glacial North Atlantic Intermediate Water) that was quantitatively distinct from preceding cold stadial events. Furthermore, our chemical proxy data show that the physical response of the WBUC during the last glacial inception was probably coupled to basin-wide changes in the water-mass composition of the deep Northwest Atlantic.
    Beschreibung: This work was supported by the Natural Environment Research Council (NERC, UK) grants NE/F002734/1, NE/I006370/1 and NE/G004021/1. We also thank the Comer Science and Education Foundation and the Leverhulme Trust for financial support.
    Beschreibung: 2013-11-30
    Schlagwort(e): Western Boundary Undercurrent ; Abrupt climate change ; North Atlantic ; Glacial ; Ocean circulation
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  • 23
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    North-South asymmetry in the modeled phytoplankton community response to climate change over the 21st century (2014)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 27 (2013): 1274–1290, doi:10.1002/2013GB004599.
    Beschreibung: Here we analyze the impact of projected climate change on plankton ecology in all major ocean biomes over the 21st century, using a multidecade (1880–2090) experiment conducted with the Community Climate System Model (CCSM-3.1) coupled ocean-atmosphere-land-sea ice model. The climate response differs fundamentally in the Northern and Southern Hemispheres for diatom and small phytoplankton biomass and consequently for total biomass, primary, and export production. Increasing vertical stratification in the Northern Hemisphere oceans decreases the nutrient supply to the ocean surface. Resulting decreases in diatom and small phytoplankton biomass together with a relative shift from diatoms to small phytoplankton in the Northern Hemisphere result in decreases in the total primary and export production and export ratio, and a shift to a more oligotrophic, more efficiently recycled, lower biomass euphotic layer. By contrast, temperature and stratification increases are smaller in the Southern compared to the Northern Hemisphere. Additionally, a southward shift and increase in strength of the Southern Ocean westerlies act against increasing temperature and freshwater fluxes to destratify the water-column. The wind-driven, poleward shift in the Southern Ocean subpolar-subtropical boundary results in a poleward shift and increase in the frontal diatom bloom. This boundary shift, localized increases in iron supply, and the direct impact of warming temperatures on phytoplankton growth result in diatom increases in the Southern Hemisphere. An increase in diatoms and decrease in small phytoplankton partly compensate such that while total production and the efficiency of organic matter export to the deep ocean increase, total Southern Hemisphere biomass does not change substantially. The impact of ecological shifts on the global carbon cycle is complex and varies across ecological biomes, with Northern and Southern Hemisphere effects on the biological production and export partially compensating. The net result of climate change is a small Northern Hemisphere-driven decrease in total primary production and efficiency of organic matter export to the deep ocean.
    Beschreibung: I. Marinov was supported by National Science Foundation (NSF) Grant ATM06-28582 while at WHOI and by NASA Grant NNX13AC92G while at Penn. I. Lima and S. Doney were supported by the Center for Microbial Oceanography, Research, and Education (CMORE), an NSF Science and Technology Center (EF-0424599).
    Beschreibung: 2014-06-20
    Schlagwort(e): Phytoplankton ; Climate change ; Ocean models
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    Satellite images of warm core ring 82-B sea surface temperature and a chronological record of major physical events affecting ring structure (2014)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-25
    Beschreibung: A chronology constructed from satellite-derived thermal imagery is presented to describe the formation and life history of warm-core ring 82-B. A comparison is made with warm-core ring 81-F in order to illustrate similarities that may be common to warm-core rings that traverse the region of the Slope Water occupied by 82-B. Particular attention is paid to discrete events identified from analysis of changes in the surface thermal field. Significant events include interactions between the ring and the Gulf Stream, warm (Gulf Stream) and cold (shelf) streamers and interaction with other vortices. The events are documented by following changes in ring size, shape, translation, and surface thermal structure. Observations determined from the infrared satellite imagery are supported by hydrography, acoustic velocity profiling and drifter trajectories.
    Beschreibung: National Science Foundation
    Schlagwort(e): Water masses ; Ocean circulation ; Marine biology ; Chemical oceanography ; Warm Core Rings
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    Materialart: Working Paper
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  • 25
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    Formation of intrathermocline lenses by eddy–wind interaction (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 606–612, doi:10.1175/JPO-D-14-0221.1.
    Beschreibung: Mesoscale intrathermocline lenses are observed throughout the World Ocean and are commonly attributed to water mass anomalies advected from a distant origin. An alternative mechanism of local generation is offered herein, in which eddy–wind interaction can create lens-shaped disturbances in the thermocline. Numerical simulations illustrate how eddy–wind-driven upwelling in anticyclones can yield a convex lens reminiscent of a mode water eddy, whereas eddy–wind-driven downwelling in cyclones produces a concave lens that thins the mode water layer (a cyclonic “thinny”). Such transformations should be observable with long-term time series in the interiors of mesoscale eddies.
    Beschreibung: Support of this research by the National Science Foundation and National Aeronautics and Space Administration is gratefully acknowledged.
    Beschreibung: 2015-08-01
    Schlagwort(e): Circulation/ Dynamics ; Eddies ; Ekman pumping/transport ; Mesoscale processes ; Models and modeling ; Ocean models ; Primitive equations model
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  • 26
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    Mixing variability in the Southern Ocean (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 966–987, doi:10.1175/JPO-D-14-0110.1.
    Beschreibung: A key remaining challenge in oceanography is the understanding and parameterization of small-scale mixing. Evidence suggests that topographic features play a significant role in enhancing mixing in the Southern Ocean. This study uses 914 high-resolution hydrographic profiles from novel EM-APEX profiling floats to investigate turbulent mixing north of the Kerguelen Plateau, a major topographic feature in the Southern Ocean. A shear–strain finescale parameterization is applied to estimate diapycnal diffusivity in the upper 1600 m of the ocean. The indirect estimates of mixing match direct microstructure profiler observations made simultaneously. It is found that mixing intensities have strong spatial and temporal variability, ranging from O(10−6) to O(10−3) m2 s−1. This study identifies topographic roughness, current speed, and wind speed as the main factors controlling mixing intensity. Additionally, the authors find strong regional variability in mixing dynamics and enhanced mixing in the Antarctic Circumpolar Current frontal region. This enhanced mixing is attributed to dissipating internal waves generated by the interaction of the Antarctic Circumpolar Current and the topography of the Kerguelen Plateau. Extending the mixing observations from the Kerguelen region to the entire Southern Ocean, this study infers a large water mass transformation rate of 17 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) across the boundary of Antarctic Intermediate Water and Upper Circumpolar Deep Water in the Antarctic Circumpolar Current. This work suggests that the contribution of mixing to the Southern Ocean overturning circulation budget is particularly significant in fronts.
    Beschreibung: AM was supported by the joint CSIRO–University of Tasmania Quantitative Marine Science (QMS) program and the 2009 CSIRO Wealth from Ocean Flagship Collaborative Fund. BMS was supported by the Australian Climate Change Science Program, jointly funded by the Department of the Environment and CSIRO. KLPs salary support was provided by Woods Hole Oceanographic Institution bridge support funds.
    Beschreibung: 2015-10-01
    Schlagwort(e): Geographic location/entity ; Southern Ocean ; Circulation/ Dynamics ; Diapycnal mixing ; Fronts ; Ocean circulation ; Topographic effects ; Atm/Ocean Structure/ Phenomena ; Mixing
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    Length scale of the finite-amplitude meanders of shelfbreak fronts (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2598–2620, doi:10.1175/JPO-D-14-0249.1.
    Beschreibung: Through combining analytical arguments and numerical models, this study investigates the finite-amplitude meanders of shelfbreak fronts characterized by sloping isopycnals outcropping at both the surface and the shelfbreak bottom. The objective is to provide a formula for the meander length scale that can explain observed frontal length scale variability and also be verified with observations. Considering the frontal instability to be a mixture of barotropic and baroclinic instability, the derived along-shelf meander length scale formula is [b1/(1 + a1S1/2)]NH/f, where N is the buoyancy frequency; H is the depth of the front; f is the Coriolis parameter; S is the Burger number measuring the ratio of energy conversion associated with barotropic and baroclinic instability; and a1 and b1 are empirical constants. Initial growth rate of the frontal instability is formulated as [b2(1 + a1S1/2)/(1 + a2αS1/2)]NH/L, where α is the bottom slope at the foot of the front, and a2 and b2 are empirical constants. The formulas are verified using numerical sensitivity simulations, and fitting of the simulated and formulated results gives a1 = 2.69, b1 = 14.65, a2 = 5.1 × 103, and b2 = 6.2 × 10−2. The numerical simulations also show development of fast-growing frontal symmetric instability when the minimum initial potential vorticity is negative. Although frontal symmetric instability leads to faster development of barotropic and baroclinic instability at later times, it does not significantly influence the meander length scale. The derived meander length scale provides a framework for future studies of the influences of external forces on shelfbreak frontal circulation and cross-frontal exchange.
    Beschreibung: WGZ and GGG were supported by the National Science Foundation through Grant OCE-1129125.
    Beschreibung: 2016-04-01
    Schlagwort(e): Circulation/ Dynamics ; Instability ; Ocean circulation ; Topographic effects ; Atm/Ocean Structure/ Phenomena ; Fronts ; Models and modeling ; Numerical analysis/modeling
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  • 28
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    Spreading of Denmark Strait overflow water in the western subpolar North Atlantic : insights from eddy-resolving simulations with a passive tracer (2016)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2913–2932, doi:10.1175/JPO-D-14-0179.1.
    Beschreibung: The oceanic deep circulation is shared between concentrated deep western boundary currents (DWBCs) and broader interior pathways, a process that is sensitive to seafloor topography. This study investigates the spreading and deepening of Denmark Strait overflow water (DSOW) in the western subpolar North Atlantic using two ° eddy-resolving Atlantic simulations, including a passive tracer injected into the DSOW. The deepest layers of DSOW transit from a narrow DWBC in the southern Irminger Sea into widespread westward flow across the central Labrador Sea, which remerges along the Labrador coast. This abyssal circulation, in contrast to the upper levels of overflow water that remain as a boundary current, blankets the deep Labrador Sea with DSOW. Farther downstream after being steered around the abrupt topography of Orphan Knoll, DSOW again leaves the boundary, forming cyclonic recirculation cells in the deep Newfoundland basin. The deep recirculation, mostly driven by the meandering pathway of the upper North Atlantic Current, leads to accumulation of tracer offshore of Orphan Knoll, precisely where a local maximum of chlorofluorocarbon (CFC) inventory is observed. At Flemish Cap, eddy fluxes carry ~20% of the tracer transport from the boundary current into the interior. Potential vorticity is conserved as the flow of DSOW broadens at the transition from steep to less steep continental rise into the Labrador Sea, while around the abrupt topography of Orphan Knoll, potential vorticity is not conserved and the DSOW deepens significantly.
    Beschreibung: This work is supported by ONR Award N00014-09-1-0587, the NSF Physical Oceanography Program, and NASA Ocean Surface Topography Science Team Program.
    Beschreibung: 2016-06-01
    Schlagwort(e): Circulation/ Dynamics ; Abyssal circulation ; Boundary currents ; Ocean circulation ; Ocean dynamics ; Potential vorticity ; Topographic effects
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    Annual and semiannual cycle of equatorial Atlantic circulation associated with basin-mode resonance (2016)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3011-3029, doi:10.1175/JPO-D-15-0248.1.
    Beschreibung: Seasonal variability of the tropical Atlantic circulation is dominated by the annual cycle, but semiannual variability is also pronounced, despite weak forcing at that period. This study uses multiyear, full-depth velocity measurements from the central equatorial Atlantic to analyze the vertical structure of annual and semiannual variations of zonal velocity. A baroclinic modal decomposition finds that the annual cycle is dominated by the fourth mode and the semiannual cycle is dominated by the second mode. Similar local behavior is found in a high-resolution general circulation model. This simulation reveals that the annual and semiannual cycles of the respective dominant baroclinic modes are associated with characteristic basinwide structures. Using an idealized, linear, reduced-gravity model to simulate the dynamics of individual baroclinic modes, it is shown that the observed circulation variability can be explained by resonant equatorial basin modes. Corollary simulations of the reduced-gravity model with varying basin geometry (i.e., square basin vs realistic coastlines) or forcing (i.e., spatially uniform vs spatially variable wind) show a structural robustness of the simulated basin modes. A main focus of this study is the seasonal variability of the Equatorial Undercurrent (EUC) as identified in recent observational studies. Main characteristics of the observed EUC including seasonal variability of transport, core depth, and maximum core velocity can be explained by the linear superposition of the dominant equatorial basin modes as obtained from the reduced-gravity model.
    Beschreibung: This study was supported by the Deutsche Forschungsgemeinschaft as part of the Sonderforschungsbereich 754 (SFB754) ‘‘Climate–Biogeochemistry Interactions in the Tropical Ocean’’ and through several research cruises with R/V Meteor, R/V Maria S. Merian, andR/VL’Atalante by the German Federal Ministry of Education and Research as part of the cooperative projects RACE (03F0605B) and SACUS (03G0837A) and by European Union 7th Framework Programme (FP7 2007–13) under Grant Agreement 603521 PREFACE project.
    Schlagwort(e): Atlantic Ocean ; Ocean circulation ; In situ oceanic observations ; Ocean models ; Seasonal cycle ; Tropical variability
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    Multi-iteration approach to studying tracer spreading using drifter data (2017)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 339-351, doi:10.1175/JPO-D-16-0165.1.
    Beschreibung: A novel multi-iteration statistical method for studying tracer spreading using drifter data is introduced. The approach allows for the best use of the available drifter data by making use of a simple iterative procedure, which results in the statistically probable map showing the likelihood that a tracer released at some source location would visit different geographical regions, along with the associated arrival travel times. The technique is tested using real drifter data in the North Atlantic. Two examples are considered corresponding to sources in the western and eastern North Atlantic Ocean, that is, Massachusetts Bay–like and Irish Sea–like sources, respectively. In both examples, the method worked well in estimating the statistics of the tracer transport pathways and travel times throughout the entire North Atlantic. The role of eddies versus mean flow is quantified using the same technique, and eddies are shown to significantly broaden the spread of a tracer. The sensitivity of the results to the size of the source domain is investigated and causes for this sensitivity are discussed.
    Beschreibung: This work was supported by the Grant OCE-1356630 from the National Science Foundation (NSF). Rypina also acknowledges NSF Grant OCE-1154641 and NASA Grant NNX14AH29G.
    Beschreibung: 2017-07-31
    Schlagwort(e): Atlantic Ocean ; Mass fluxes/transport ; Ocean circulation ; Trajectories ; Statistics
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    Recent wind-driven variability in Atlantic water mass distribution and meridional overturning circulation (2017)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 633-647, doi:10.1175/JPO-D-16-0089.1.
    Beschreibung: Interannual variability in the volumetric water mass distribution within the North Atlantic Subtropical Gyre is described in relation to variability in the Atlantic meridional overturning circulation. The relative roles of diabatic and adiabatic processes in the volume and heat budgets of the subtropical gyre are investigated by projecting data into temperature coordinates as volumes of water using an Argo-based climatology and an ocean state estimate (ECCO version 4). This highlights that variations in the subtropical gyre volume budget are predominantly set by transport divergence in the gyre. A strong correlation between the volume anomaly due to transport divergence and the variability of both thermocline depth and Ekman pumping over the gyre suggests that wind-driven heave drives transport anomalies at the gyre boundaries. This wind-driven heaving contributes significantly to variations in the heat content of the gyre, as do anomalies in the air–sea fluxes. The analysis presented suggests that wind forcing plays an important role in driving interannual variability in the Atlantic meridional overturning circulation and that this variability can be unraveled from spatially distributed hydrographic observations using the framework presented here.
    Beschreibung: DGE was supported by a Natural Environment Research Council studentship award at the University of Southampton. JMT’s contribution was supported by the U.S. National Science Foundation (Grant OCE-1332667). GF’s contribution was supported by the U.S. National Science Foundation through Grant OCE-0961713 and by the U.S. National Oceanic and Atmospheric Administration through Grant NA10OAR4310135. The contributions of JDZ and AJGN were supported by the NERC Grant ‘‘Climate scale analysis of air and water masses’’ (NE/ K012932/1). ACNG gratefully acknowledges support from the Leverhulme Trust, the Royal Society, and the Wolfson Foundation. LY was supported by NASA Ocean Vector Wind Science Team (OVWST) activities under Grant NNA10AO86G.
    Schlagwort(e): North Atlantic Ocean ; Atmosphere-ocean interaction ; Ekman pumping/transport ; Ocean circulation ; Water masses ; Inverse methods
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    The interaction of recirculation gyres and a deep boundary current (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 573-590, doi:10.1175/JPO-D-17-0206.1.
    Beschreibung: Motivated by the proximity of the Northern Recirculation Gyre and the deep western boundary current in the North Atlantic, an idealized model is used to investigate how recirculation gyres and a deep flow along a topographic slope interact. In this two-layer quasigeostrophic model, an unstable jet imposed in the upper layer generates barotropic recirculation gyres. These are maintained by an eddy-mean balance of potential vorticity (PV) in steady state. The authors show that the topographic slope can constrain the northern recirculation gyre meridionally and that the gyre’s adjustment to the slope leads to increased eddy PV fluxes at the base of the slope. When a deep current is present along the topographic slope in the lower layer, these eddy PV fluxes stir the deep current and recirculation gyre waters. Increased proximity to the slope dampens the eddy growth rate within the unstable jet, altering the geometry of recirculation gyre forcing and leading to a decrease in overall eddy PV fluxes. These mechanisms may shape the circulation in the western North Atlantic, with potential feedbacks on the climate system.
    Beschreibung: We gratefully acknowledge an AMS graduate fellowship (IALB) and U.S. National Science Foundation Grants OCE-1332667 and 1332834 (IALB and JMT).
    Beschreibung: 2018-09-06
    Schlagwort(e): Boundary currents ; Meridional overturning circulation ; Mesoscale processes ; Ocean circulation ; Potential vorticity ; Quasigeostrophic models
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  • 33
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    Comment on “Abyssal upwelling and downwelling driven by near-boundary mixing” (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 739-748, doi:10.1175/JPO-D-17-0089.1.
    Beschreibung: McDougall and Ferrari have estimated the global deep upward diapycnal flow in the boundary layer overlying continental slopes that must balance both downward diapycnal flow in the deep interior and the formation of bottom water around Antarctica. The decrease of perimeter of isopycnal surfaces with depth and the observed decay with height above bottom of turbulent dissipation in the deep ocean play a key role in their estimate. They argue that because the perimeter of seamounts increases with depth, the net effect of mixing around seamounts is to produce net downward diapycnal flow. While this is true along much of a seamount, it is shown here that diapycnal flow of the densest water around the seamount is upward, with buoyancy being transferred from water just above. The same is true for midocean ridges, whose perimeter is constant with depth. It is argued that mixing around seamounts and especially midocean ridges contributes positively to the global deep overturning circulation, reducing the amount of turbulence demanded over the continental slopes to balance the buoyancy budget for the bottom and deep water.
    Beschreibung: This work was supported by National Science Foundation Grant OCE- 1232962.
    Beschreibung: 2018-09-29
    Schlagwort(e): Abyssal circulation ; Boundary currents ; Buoyancy ; Diapycnal mixing ; Mass fluxes/transport ; Ocean circulation
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    A note on interior pathways in the meridional overturning circulation (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 643-646, doi:10.1175/JPO-D-17-0240.1.
    Beschreibung: A simple oceanic model is presented for source–sink flow on the β plane to discuss the pathways from source to sink when transport boundary layers have large enough Reynolds numbers to be inertial in their dynamics. A representation of the flow as a Fofonoff gyre, suggested by prior work on inertial boundary layers and eddy-driven circulations in two-dimensional turbulent flows, indicates that even when the source and sink are aligned along the same western boundary the flow must intrude deep into the interior before exiting at the sink. The existence of interior pathways for the flow is thus an intrinsic property of an inertial circulation and is not dependent on particular geographical basin geometry.
    Beschreibung: 2018-09-12
    Schlagwort(e): Abyssal circulation ; Bottom currents ; Nonlinear dynamics ; Ocean circulation ; Ocean dynamics ; Potential vorticity
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    Diapycnal mixing in the Southern Ocean diagnosed using the DIMES tracer and realistic velocity fields (2018)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 2615-2634, doi:10.1002/2017JC013536.
    Beschreibung: In this work, we use realistic isopycnal velocities with a 3-D eddy diffusivity to advect and diffuse a tracer in the Antarctic Circumpolar Current, beginning in the Southeast Pacific and progressing through Drake Passage. We prescribe a diapycnal diffusivity which takes one value in the SE Pacific west of 678W and another value in Drake Passage east of that longitude, and optimize the diffusivities using a cost function to give a best fit to experimental data from the DIMES (Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean) tracer, released near the boundary between the Upper and Lower Circumpolar Deep Water. We find that diapycnal diffusivity is enhanced 20-fold in Drake Passage compared with the SE Pacific, consistent with previous estimates obtained using a simpler advection-diffusion model with constant, but different, zonal velocities east and west of 678W. Our result shows that diapycnal mixing in the ACC plays a significant role in transferring buoyancy within the Meridional Overturning Circulation.
    Beschreibung: UK Natural Environment Research Council Grant Numbers: NE/F020252/1 , NE/N018028/1 , NE/J007757/1; US National Science Foundation Grant Numbers: OCE 0622825 , OCE 1232962
    Beschreibung: 2018-09-26
    Schlagwort(e): Diapycnal mixing ; Ocean circulation ; Tracer experiment ; Ocean model
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    Propagation of North Atlantic Deep Water anomalies (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1831-1848, doi:10.1175/JPO-D-18-0068.1.
    Beschreibung: We present a simplified theory using reduced-gravity equations for North Atlantic Deep Water (NADW) and its variation driven by high-latitude deep-water formation. The theory approximates layer thickness on the eastern boundary with domain-averaged layer thickness and, in tandem with a mass conservation argument, retains fundamental physics for cross-equatorial flows on interannual and longer forcing time scales. Layer thickness anomalies are driven by a time-dependent northern boundary condition that imposes a southward volume flux representative of a variable source of NADW and damped by diapycnal mixing throughout the basin. Moreover, an outflowing southern boundary condition imposes a southward volume flux that generally differs from the volume flux at the northern boundary, giving rise to temporal storage of NADW within the Atlantic basin. Closed form analytic solutions for the amplitude and phase are provided when the variable source of NADW is sinusoidal. We provide a nondimensional analysis that demonstrates that solution behavior is primarily controlled by two parameters that characterize the meridional extent of the southern basin and the width of the basin relative to the equatorial deformation radius. Similar scaling applied to the time-lagged equations of Johnson and Marshall provides a clear connection to their results. Numerical simulations of reduced-gravity equations agree with analytic predictions in linear, turbulent, and diabatic regimes. The theory introduces a simple analytic framework for studying idealized buoyancy- and wind-driven cross-equatorial flows on interannual and longer time scales.
    Beschreibung: This research was supported by the National Science Foundation under Grant OCE- 1634468.
    Beschreibung: 2019-02-15
    Schlagwort(e): North Atlantic Ocean ; Tropics ; Meridional overturning circulation ; Ocean circulation ; Shallow-water equations
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    Sinking of dense North Atlantic waters in a global ocean model : location and controls (2018)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 3563-3576, doi:10.1029/2017JC013329.
    Beschreibung: We investigate the characteristics of the sinking of dense waters in the North Atlantic Ocean that constitute the downwelling limb of the Atlantic Meridional Overturning Circulation (AMOC) as simulated by two global ocean models: an eddy‐permitting model at 1/4° resolution and its coarser 1° counterpart. In line with simple geostrophic considerations, it is shown that the sinking predominantly occurs in a narrow region close to the continental boundary in both model simulations. That is, the regions where convection is deepest do not coincide with regions where most dense waters sink. The amount of near‐boundary sinking that occurs varies regionally. For the 1/4° resolution model, these variations are in quantitative agreement with a relation based on geostrophy and a thermodynamic balance between buoyancy loss and alongshore advection of density, which links the amount of sinking to changes in density along the edge of the North Atlantic Ocean. In the 1° model, the amount and location of sinking appears not to be governed by this simple relation, possibly due to the large impact of overflows and nonnegligible cross‐shore density advection. If this poor representation of the processes governing the sinking of dense waters in the North Atlantic Ocean is a generic feature of such low‐resolution models, the response of the AMOC to changes in climate simulated by this type of models needs to be evaluated with care.
    Beschreibung: NWO (Netherlands Scientific Research foundation) VIDI Grant Number: 864.13.011; National Science Foundation Grant Numbers: OCE‐1534618, OCE‐1558742
    Schlagwort(e): Ocean circulation ; Climate
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    Wind-driven circulation in a shelf valley. Part II : Dynamics of the along-valley velocity and transport (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 883-904, doi:10.1175/JPO-D-17-0084.1.
    Beschreibung: The dynamics controlling the along-valley (cross shelf) flow in idealized shallow shelf valleys with small to moderate Burger number are investigated, and analytical scales of the along-valley flows are derived. This paper follows Part I, which shows that along-shelf winds in the opposite direction to coastal-trapped wave propagation (upwelling regime) force a strong up-valley flow caused by the formation of a lee wave. In contrast, along-shelf winds in the other direction (downwelling regime) do not generate a lee wave and consequently force a relatively weak net down-valley flow. The valley flows in both regimes are cyclostrophic with 0(1) Rossby number. A major difference between the two regimes is the along-shelf length scales of the along-valley flows L. In the upwelling regime Ls, depends on the valley width W, and the wavelength lambda(1w) of the coastal-trapped lee wave arrested by the along-shelf flow U-s. In the downwelling regime L depends on the inertial length scale U-s|'f and W-c. The along-valley velocity scale in the upwelling regime, given by V-u approximate to root pi H-c/H-s integral W-c lambda(1w)/2 pi L-x (1+L-x(2)/L-c(2))(-1) e(-(pi Wc)/(lambda 1w),) is based on potential vorticity (PV) conservation and lee-wave dynamics (Hs and H, are the shelf and valley depth scales, respectively, and fis the Coriolis parameter). The velocity scale in the downwelling regime, given by |v(d)| approximate to (H-s/H-s)[1 + (L-x(2)/L-x(2))](-1) fL, is based on PV conservation. The velocity scales are validated by the numerical sensitivity simulations and can be useful for observational studies of along -valley transports. The work provides a framework for investigating cross -shelf transport induced by irregular shelf bathymetry and calls for future studies of this type under realistic environmental conditions and over a broader parameter space.
    Beschreibung: Both WGZ and SJL were supported by the National Science Foundation (NSF) through Grant OCE 1154575.WGZis also supported by the NSF Grant OCE 1634965 and SJL by NSF Grant OCE 1558874.
    Beschreibung: 2018-10-16
    Schlagwort(e): Ocean circulation ; Topographic effects ; Upwelling/downwelling ; Waves, oceanic ; Wind stress ; Ocean models
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    The three-dimensional steady circulation in a homogenous ocean induced by a stationary hurricane (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1441–1457, doi:10.1175/2010JPO4293.1.
    Beschreibung: Based on the classical Ekman layer theory, a simple analytical solution of the steady flow induced by a stationary hurricane in a homogenous ocean is discussed. The model consists of flow converging in an inward spiral in the deeper layer and diverging in the upper layer. The simple analytical model indicates that both the upwelling flux and the horizontal transport increase linearly with increasing radius of maximum winds. Furthermore, they both have a parabolic relationship with the maximum wind speed. The Coriolis parameter also affects the upwelling flux: the response to a hurricane is stronger at low latitudes than that at middle latitudes. Numerical solutions based on a regional version of an ocean general circulation model are similar to the primary results obtained through the analytical solution. Thus, the simplifications made in formulating the analytical solution are reasonable. Although the analytical solution in this paper is sought for a rather idealized ocean, it can help to make results from the more complicated numerical model understandable. These conceptual models provide a theoretical limit structure of the oceanic response to a moving hurricane over a stratified ocean.
    Beschreibung: ZML was supported by CAS (kzcx2-yw-226, SQ200813), NSFC under Grants 40906009 and 40776008, and Dr. Xiaodong Shang through ‘‘100 Talents Program’’ of CAS.
    Schlagwort(e): Hurricanes ; Ocean circulation
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    Wave-driven inner-shelf motions on the Oregon coast (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2942-2956, doi:10.1175/2009JPO4041.1.
    Beschreibung: Recent work by S. Lentz et al. documents offshore transport in the inner shelf due to a wave-driven return flow associated with the Hasselmann wave stress (the Stokes–Coriolis force). This analysis is extended using observations from the central Oregon coast to identify the wave-driven return flow present and quantify the potential bias of wind-driven across-shelf exchange by unresolved wave-driven circulation. Using acoustic Doppler current profiler (ADCP) measurements at six stations, each in water depths of 13–15 m, observed depth-averaged, across-shelf velocities were generally correlated with theoretical estimates of the proposed return flow. During times of minimal wind forcing, across-shelf velocity profiles were vertically sheared, with stronger velocities near the top of the measured portion of the water column, and increased in magnitude with increasing significant wave height, consistent with circulation due to the Hasselmann wave stress. Yet velocity magnitudes and vertical shears were stronger than that predicted by linear wave theory, and more similar to the stratified “summer” velocity profiles described by S. Lentz et al. Additionally, substantial temporal and spatial variability of the wave-driven return flow was found, potentially due to changing wind and wave conditions as well as local bathymetric variability. Despite the wave-driven circulation found, subtracting estimates of the return flow from the observed across-shelf velocity had no significant effect on estimates of the across-shelf exchange due to along-shelf wind forcing at these water depths along the Oregon coast during summer.
    Beschreibung: This work was performed with the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO), funded primarily by the Gordon and Betty Moore Foundation and David and Lucile Packard Foundation. SL acknowledges support from NSF Ocean Science Grant #OCE-0548961. AK acknowledges support from the WHOI Coastal Ocean Institute Fellowship.
    Schlagwort(e): Waves, oceanic ; Ekman pumping/transport ; Coastlines ; Ocean circulation ; Gravity waves
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  • 41
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    Abrupt transitions and hysteresis in thermohaline laboratory models (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1231-1243, doi:10.1175/2008JPO4087.1.
    Beschreibung: As a driving parameter is slowly altered, thermohaline ocean circulation models show either a smooth evolution of a mode of flow or an abrupt transition of temperature and salinity fields from one mode to another. An abrupt transition might occur at one value or over a range of the driving parameter. The latter has hysteresis because the mode in this range depends on the history of the driving parameter. Although assorted ocean circulation models exhibit abrupt transitions, such transitions have not been directly observed in the ocean. Therefore, laboratory experiments have been conducted to seek and observe actual (physical) abrupt thermohaline transitions. An experiment closely duplicating Stommel’s box model possessed abrupt transitions in temperature and salinity with distinct hysteresis. Two subsequent experiments with more latitude for internal circulation in the containers possessed abrupt transitions over a much smaller range of hysteresis. Therefore, a new experiment with even more latitude for internal circulation was designed and conducted. A large tank of constantly renewed freshwater at room temperature had a smaller cavity in the bottom heated from below with saltwater steadily pumped in. The cavity had either a salt mode, consisting of the cavity filled with heated salty water with an interface at the cavity top, or a temperature mode, in which the heat and saltwater were removed from the cavity by convection. There was no measurable hysteresis between the two modes. Possible reasons for such small hysteresis are discussed.
    Beschreibung: Support is gratefully acknowledged from the Woods Hole Oceanographic Institution Climate Change Institute, the National Science Foundation, Physical Oceanography Section under Grant OCE-0081179, and the Paul M. Fye Chair of the Woods Hole Oceanographic Institution.
    Schlagwort(e): Thermohaline circulation ; Experimental design ; Ocean circulation ; Temperature ; Salinity
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  • 42
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    The importance of tidal and lateral asymmetries in stratification to residual circulation in partially mixed estuaries (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1496-1511, doi:10.1175/jpo3071.1.
    Beschreibung: Measurements collected in the York River estuary, Virginia, demonstrate the important impact that tidal and lateral asymmetries in turbulent mixing have on the tidally averaged residual circulation. A reduction in turbulent mixing during the ebb phase of the tide caused by tidal straining of the axial density gradient results in increased vertical velocity shear throughout the water column during the ebb tide. In the absence of significant lateral differences in turbulent mixing, the enhanced ebb-directed transport caused by tidal straining is balanced by a reduction in the net seaward-directed barotropic pressure gradient, resulting in laterally uniform two-layer residual flow. However, the channel–shoal morphology of many drowned river valley estuaries often leads to lateral gradients in turbulent mixing. Tidal straining may then lead to tidal asymmetries in turbulent mixing near the deeper channel while the neighboring shoals remain relatively well mixed. As a result, the largest lateral asymmetries in turbulent mixing occur at the end of the ebb tide when the channel is significantly more stratified than the shoals. The reduced friction at the end of ebb delays the onset of the flood tide, increasing the duration of ebb in the channel. Conversely, over the shoal regions where stratification is more inhibited by tidal mixing, there is greater friction and the transition from ebb to flood occurs more rapidly. The resulting residual circulation is seaward over the channel and landward over the shoal. The shoal–channel segregation of this barotropically induced estuarine residual flow is opposite to that typically associated with baroclinic estuarine circulation over channel–shoal bathymetry.
    Beschreibung: Support for this research was provided by the National Science Foundation Division of Ocean Sciences Grant OCE- 9984941.
    Schlagwort(e): Tides ; Ocean circulation ; Estuaries ; Turbulence
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  • 43
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    Impact of Labrador Sea convection on the North Atlantic meridional overturning circulation (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2207-2227, doi:10.1175/jpo3178.1.
    Beschreibung: The overturning and horizontal circulations of the Labrador Sea are deduced from a composite vertical section across the basin. The data come from the late-spring/early-summer occupations of the World Ocean Circulation Experiment (WOCE) AR7W line, during the years 1990–97. This time period was chosen because it corresponded to intense wintertime convection—the deepest and densest in the historical record—suggesting that the North Atlantic meridional overturning circulation (MOC) would be maximally impacted. The composite geostrophic velocity section was referenced using a mean lateral velocity profile from float data and then subsequently adjusted to balance mass. The analysis was done in depth space to determine the net sinking that results from convection and in density space to determine the diapycnal mass flux (i.e., the transformation of light water to Labrador Sea Water). The mean overturning cell is calculated to be 1 Sv (1 Sv ≡ 106 m3 s−1), as compared with a horizontal gyre of 18 Sv. The total water mass transformation is 2 Sv. These values are consistent with recent modeling results. The diagnosed heat flux of 37.6 TW is found to result predominantly from the horizontal circulation, both in depth space and density space. These results suggest that the North Atlantic MOC is not largely impacted by deep convection in the Labrador Sea.
    Beschreibung: This work was funded by the National Science Foundation through Grants OCE-0450658 (RP) and OCE-024978 (MS).
    Schlagwort(e): Convection ; Ocean circulation ; North Atlantic
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  • 44
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    The role of advection, straining, and mixing on the tidal variability of estuarine stratification (2012)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 855–868, doi:10.1175/JPO-D-10-05010.1.
    Beschreibung: Data from the Hudson River estuary demonstrate that the tidal variations in vertical salinity stratification are not consistent with the patterns associated with along-channel tidal straining. These observations result from three additional processes not accounted for in the traditional tidal straining model: 1) along-channel and 2) lateral advection of horizontal gradients in the vertical salinity gradient and 3) tidal asymmetries in the strength of vertical mixing. As a result, cross-sectionally averaged values of the vertical salinity gradient are shown to increase during the flood tide and decrease during the ebb. Only over a limited portion of the cross section does the observed stratification increase during the ebb and decrease during the flood. These observations highlight the three-dimensional nature of estuarine flows and demonstrate that lateral circulation provides an alternate mechanism that allows for the exchange of materials between surface and bottom waters, even when direct turbulent mixing through the pycnocline is prohibited by strong stratification.
    Beschreibung: The funding for this research was obtained from NSF Grant OCE-08-25226.
    Beschreibung: 2012-11-01
    Schlagwort(e): Mixing ; Ocean circulation ; Shear structure/flows ; Transport ; Turbulence
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  • 45
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    The effects of thermohaline circulation on wind-driven circulation in the South China Sea (2013)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2283–2296, doi:10.1175/JPO-D-11-0227.1.
    Beschreibung: The dynamic influence of thermohaline circulation on wind-driven circulation in the South China Sea (SCS) is studied using a simple reduced gravity model, in which the upwelling driven by mixing in the abyssal ocean is treated in terms of an upward pumping distributed at the base of the upper layer. Because of the strong upwelling of deep water, the cyclonic gyre in the northern SCS is weakened, but the anticyclonic gyre in the southern SCS is intensified in summer, while cyclonic gyres in both the southern and northern SCS are weakened in winter. For all seasons, the dynamic influence of thermohaline circulation on wind-driven circulation is larger in the northern SCS than in the southern SCS. Analysis suggests that the upwelling associated with the thermohaline circulation in the deep ocean plays a crucial role in regulating the wind-driven circulation in the upper ocean.
    Beschreibung: G. Wang is supported by the National Science Foundation of China (NSFC Grants 41125019, 40725017, and 40976017).D.Chen is supported by grants from the Ministry of Science and Technology (2010DFA21012), the State Oceanic Administration (201105018), and the NSFC (91128204).
    Beschreibung: 2013-06-01
    Schlagwort(e): Abyssal circulation ; Dynamics ; Ocean circulation ; Upwelling/downwelling
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  • 46
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    An inertial model of the interaction of Ekman layers and planetary islands (2014)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1398–1406, doi:10.1175/JPO-D-13-028.1.
    Beschreibung: An adiabatic, inertial, and quasigeostrophic model is used to discuss the interaction of surface Ekman transport with an island. The theory extends the recent work of Spall and Pedlosky to include an analytical and nonlinear model for the interaction. The presence of an island that interrupts a uniform Ekman layer transport raises interesting questions about the resulting circulation. The consequential upwelling around the island can lead to a local intake of fluid from the geostrophic region beneath the Ekman layer or to a more complex flow around the island in which the fluid entering the Ekman layer on one portion of the island's perimeter is replaced by a flow along the island's boundary from a downwelling region located elsewhere on the island. This becomes especially pertinent when the flow is quasigeostrophic and adiabatic. The oncoming geostrophic flow that balances the offshore Ekman flux is largely diverted around the island, and the Ekman flux is fed by a transfer of fluid from the western to the eastern side of the island. As opposed to the linear, dissipative model described earlier, this transfer takes place even in the absence of a topographic skirt around the island. The principal effect of topography in the inertial model is to introduce an asymmetry between the circulation on the northern and southern sides of the island. The quasigeostrophic model allows a simple solution to the model problem with topography and yet the resulting three-dimensional circulation is surprisingly complex with streamlines connecting each side of the island.
    Beschreibung: This research was supported in part by NSF Grant OCE Grant 0925061.
    Schlagwort(e): Baroclinic flows ; Large-scale motions ; Nonlinear dynamics ; Ocean circulation ; Ocean dynamics ; Topographic effects
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  • 47
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    Warm core rings : an interdisciplinary study of warm core ring physics, chemistry, and biology; R/V Endeavor, R/V Knorr, R/V Oceanus April 1982 cruise reports (2014)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-25
    Schlagwort(e): Endeavor (Ship: 1976-) Cruise EN83 ; Knorr (Ship : 1970-) Cruise KN93 ; Oceanus (Ship : 1975-) Cruise OC118 ; Ocean circulation ; Marine biology ; Chemical oceanography ; Warm Core Rings
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    Materialart: Working Paper
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  • 48
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    Year-to-year reoutcropping of Eighteen Degree Water in an eddy-resolving ocean simulation (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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):1189–1204, doi:10.1175/JPO-D-14-0122.1.
    Beschreibung: Winter outcropping of the Eighteen Degree Water (EDW) and its subsequent dispersion are studied using a ° eddy-resolving simulation of the Family of Linked Atlantic Modeling Experiments (FLAME). Outcropped EDW columns in the model simulations are detected in each winter from 1990 to 1999, and particles are deployed in the center of each outcropped EDW column. Subsequently, the trajectories of these particles are calculated for the following 5 yr. The particles slowly spread away from the outcropping region into the nonoutcropping/subducted EDW region south of ~30°N and eventually to the non-EDW region in the greater subtropical gyre. Approximately 30% of the particles are found in non-EDW waters 1 yr after deployment; after 5 yr, only 25% of the particles are found within EDW. The reoutcropping time is defined as the number of years between when a particle is originally deployed in an outcropping EDW column and when that particle is next found in an outcropping EDW column. Of the particles, 66% are found to reoutcrop as EDW in 1 yr, and less than 5% of the particles outcrop in each of the subsequent 4 yr. While the individual trajectories exhibit significant eddy-like motions, the time scale of reoutcropping is primarily set by the mean circulation. The dominance of reoutcropping in 1 yr suggests that EDW outcropping contributes considerably to the persistence of surface temperature anomalies from one winter to the next, that is, the reemergence of winter sea surface temperature anomalies.
    Beschreibung: We gratefully acknowledge the support from the NSF OCE Physical Oceanography program (NSF OCE-0961090 to Y-OK and J-JP; NSF OCE-0960776 to MSL and SFG; and NSF OCE-1242989 to Y-OK).
    Beschreibung: 2015-10-01
    Schlagwort(e): Circulation/ Dynamics ; Ocean circulation ; Atm/Ocean Structure/ Phenomena ; Water masses
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  • 49
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    On the crossover of boundary currents in an idealized model of the Red Sea (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 1410–1425, doi:10.1175/JPO-D-14-0192.1.
    Beschreibung: The west-to-east crossover of boundary currents has been seen in mean circulation schemes from several past models of the Red Sea. This study investigates the mechanisms that produce and control the crossover in an idealized, eddy-resolving numerical model of the Red Sea. The authors also review the observational evidence and derive an analytical estimate for the crossover latitude. The surface buoyancy loss increases northward in the idealized model, and the resultant mean circulation consists of an anticyclonic gyre in the south and a cyclonic gyre in the north. In the midbasin, the northward surface flow crosses from the western boundary to the eastern boundary. Numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0, β, and the meridional gradient of surface buoyancy forcing. In the analytical estimate, which is based on quasigeostrophic, β-plane dynamics, the crossover is predicted to lie at the latitude where the net potential vorticity advection (including an eddy component) is zero. Various terms in the potential vorticity budget can be estimated using a buoyancy budget, a thermal wind balance, and a parameterization of baroclinic instability.
    Beschreibung: This work is supported by Award USA 00002, KSA 00011, and KSA 00011/02 made by King Abdullah University of Science and Technology (KAUST), by National Science Foundation Grants OCE0927017, OCE1154641, and OCE85464100, and by the Woods Hole Oceanographic Institution Academic Program Office.
    Beschreibung: 2015-11-01
    Schlagwort(e): Circulation/ Dynamics ; Boundary currents ; Buoyancy ; Ocean circulation ; Ocean dynamics
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  • 50
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    The interaction of an eastward-flowing current and an island : sub- and supercritical flow (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2806–2819, doi:10.1175/JPO-D-15-0061.1.
    Beschreibung: An eastward-flowing current of a homogeneous fluid with velocity U, contained in a channel of width L, impinges on an island of width of O(L), and the resulting interaction and dynamics are studied for values of the supercriticality parameter, b = βL2/U, both larger and smaller than π2. The former case is subcritical with respect to Rossby waves, and the latter is supercritical. The nature of the flow field depends strongly on b, and in particular, the nature of the flow around the island and the proportion of the flow passing to the north or south of the island are sensitive to b and to the position of the island in the channel. The problem is studied analytically in a relatively simple, nonlinear quasigeostrophic and adiabatic framework and numerically with a shallow-water model that allows a qualitative extension of the results to the equator. Although the issues involved are motivated by the interaction of the Equatorial Undercurrent and the Galapagos Islands, the analysis presented here focuses on the fundamental issue of the distinctive nature of the flow as a function of Rossby wave criticality.
    Beschreibung: Supported by the National Science Foundation Grant OCE-0959381.
    Beschreibung: 2016-05-01
    Schlagwort(e): Circulation/ Dynamics ; Ocean circulation ; Ocean dynamics ; Waves, oceanic
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    Latitudinal structure of the meridional overturning circulation variability on interannual to decadal time scales in the North Atlantic Ocean (2020)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2020. 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 33(9), (2020): 3845-3862, doi:10.1175/JCLI-D-19-0215.1.
    Beschreibung: The latitudinal structure of the Atlantic meridional overturning circulation (AMOC) variability in the North Atlantic is investigated using numerical results from three ocean circulation simulations over the past four to five decades. We show that AMOC variability south of the Labrador Sea (53°N) to 25°N can be decomposed into a latitudinally coherent component and a gyre-opposing component. The latitudinally coherent component contains both decadal and interannual variabilities. The coherent decadal AMOC variability originates in the subpolar region and is reflected by the zonal density gradient in that basin. It is further shown to be linked to persistent North Atlantic Oscillation (NAO) conditions in all three models. The interannual AMOC variability contained in the latitudinally coherent component is shown to be driven by westerlies in the transition region between the subpolar and the subtropical gyre (40°–50°N), through significant responses in Ekman transport. Finally, the gyre-opposing component principally varies on interannual time scales and responds to local wind variability related to the annual NAO. The contribution of these components to the total AMOC variability is latitude-dependent: 1) in the subpolar region, all models show that the latitudinally coherent component dominates AMOC variability on interannual to decadal time scales, with little contribution from the gyre-opposing component, and 2) in the subtropical region, the gyre-opposing component explains a majority of the interannual AMOC variability in two models, while in the other model, the contributions from the coherent and the gyre-opposing components are comparable. These results provide a quantitative decomposition of AMOC variability across latitudes and shed light on the linkage between different AMOC variability components and atmospheric forcing mechanisms.
    Beschreibung: The authors gratefully acknowledge support from the Physical Oceanography Program of the U.S. National Science Foundation (Awards OCE-1756143 and OCE-1537136) and the Climate Program Office of the National Oceanic and Atmospheric Administration (Award NA15OAR4310088). Gratitude is extended to Claus Böning and Arne Biastoch who shared ORCA025 output. S. Zou thanks F. Li, M. Buckley, and L. Li for helpful discussions. We also thank three anonymous reviewers for helpful suggestions.
    Schlagwort(e): Deep convection ; Ocean circulation ; Thermocline circulation
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  • 52
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    The Kuroshio Extension northern recirculation gyre : profiling float measurements and forcing mechanism (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1764-1779, doi:10.1175/2008JPO3921.1.
    Beschreibung: Middepth, time-mean circulation in the western North Pacific Ocean (28°–45°N, 140°–165°E) is investigated using drift information from the profiling floats deployed in the Kuroshio Extension System Study (KESS) and the International Argo programs. A well-defined, cyclonic recirculation gyre (RG) is found to exist north of the Kuroshio Extension jet, confined zonally between the Japan Trench (145°E) and the Shatsky Rise (156°E), and bordered to the north by the subarctic boundary along 40°N. This northern RG, which is simulated favorably in the eddy-resolving OGCM for the Earth Simulator (OFES) hindcast run model, has a maximum volume transport at 26.4 Sv across 159°E and its presence persists on the interannual and longer time scales. An examination of the time-mean x-momentum balance from the OFES hindcast run output reveals that horizontal convergence of Reynolds stresses works to accelerate both the eastward-flowing Kuroshio Extension jet and a westward mean flow north of the meandering jet. The fact that the northern RG is eddy driven is further confirmed by examining the turbulent Sverdrup balance, in which convergent eddy potential vorticity fluxes are found to induce the cyclonic RG across the background potential vorticity gradient field. For the strength of the simulated northern RG, the authors find the eddy dissipation effect to be important as well.
    Beschreibung: This study was supported by NSF through Grant OCE-0220680 (UH) and OCE-0220161 (WHOI).
    Schlagwort(e): Gyres ; Ocean circulation ; Profilers ; Jets ; Transport
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  • 53
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    The mechanical energy input to the ocean induced by tropical cyclones (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1253-1266, doi:10.1175/2007JPO3786.1.
    Beschreibung: Wind stress and tidal dissipation are the most important sources of mechanical energy for maintaining the oceanic general circulation. The contribution of mechanical energy due to tropical cyclones can be a vitally important factor in regulating the oceanic general circulation and its variability. However, previous estimates of wind stress energy input were based on low-resolution wind stress data in which strong nonlinear events, such as tropical cyclones, were smoothed out. Using a hurricane–ocean coupled model constructed from an axisymmetric hurricane model and a three-layer ocean model, the rate of energy input to the world’s oceans induced by tropical cyclones over the period from 1984 to 2003 was estimated. The energy input is estimated as follows: 1.62 TW to the surface waves and 0.10 TW to the surface currents (including 0.03 TW to the near-inertial motions). The rate of gravitational potential energy increase due to tropical cyclones is 0.05 TW. Both the energy input from tropical cyclones and the increase of gravitational potential energy of the ocean show strong interannual and decadal variability with an increasing rate of 16% over the past 20 years. The annual mean diapycnal upwelling induced by tropical cyclones over the past 20 years is estimated as 39 Sv (Sv ≡ 106 m3 s−1). Owing to tropical cyclones, diapycnal mixing in the upper ocean (below the mixed layer) is greatly enhanced. Within the regimes of strong activity of tropical cyclones, the increase of diapycnal diffusivity is on the order of (1 − 6) × 10−4 m2 s−1. The tropical cyclone–related energy input and diapycnal mixing may play an important role in climate variability, ecology, fishery, and environments.
    Beschreibung: LLL and WW were supported by the National Basic Research Priorities Programmer of China through Grant 2007CB816004 and National Outstanding Youth Natural Science Foundation of China FIG. 15. Annual-mean vertical diffusivity induced by tropical cyclones from 1984 to 2003 (units: 10 4 m2 s 1): (right) the horizontal distribution and (left) the zonally averaged vertical diffusivity. JUNE 2008 L IU ET AL . 1265 under Grant 40725017. RXH was supported by the W. Alan Clark Chair from Woods Hole Oceanographic Institution.
    Schlagwort(e): Tropical cyclones ; Ocean circulation ; Wind stress ; Mixing ; Interannual variability
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  • 54
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    How does Labrador Sea Water enter the deep western boundary current? (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 968-983, doi:10.1175/2007JPO3807.1.
    Beschreibung: Labrador Sea Water (LSW), a dense water mass formed by convection in the subpolar North Atlantic, is an important constituent of the meridional overturning circulation. Understanding how the water mass enters the deep western boundary current (DWBC), one of the primary pathways by which it exits the subpolar gyre, can shed light on the continuity between climate conditions in the formation region and their downstream signal. Using the trajectories of (profiling) autonomous Lagrangian circulation explorer [(P)ALACE] floats, operating between 1996 and 2002, three processes are evaluated for their role in the entry of Labrador Sea Water in the DWBC: 1) LSW is formed directly in the DWBC, 2) eddies flux LSW laterally from the interior Labrador Sea to the DWBC, and 3) a horizontally divergent mean flow advects LSW from the interior to the DWBC. A comparison of the heat flux associated with each of these three mechanisms suggests that all three contribute to the transformation of the boundary current as it transits the Labrador Sea. The formation of LSW directly in the DWBC and the eddy heat flux between the interior Labrador Sea and the DWBC may play leading roles in setting the interannual variability of the exported water mass.
    Beschreibung: We are also grateful to the NSF for their support of this research.
    Schlagwort(e): Boundary currents ; Water masses ; Ocean circulation ; Lagrangian circulation
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  • 55
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    Circulation and exchange in choked marginal seas (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2639-2661, doi:10.1175/2008JPO3946.1.
    Beschreibung: A theory for the exchange between a rotating, buoyancy-forced marginal sea and an ocean is developed and tested numerically. Cooling over the marginal sea leads to sinking and sets up a two-layer exchange flow, with a warm surface layer entering from the ocean and a cool layer exiting at depth. The connecting strait is sufficiently narrow and shallow to cause the exchange flow to be hydraulically controlled. The incoming surface layer forms a baroclinically unstable boundary current that circles the marginal sea in a cyclonic sense and feeds heat to the interior by way of eddies. Consistent with the overall heat and volume balances for the marginal sea, there is a continuous family of hydraulically controlled states with critical flow at the most constricted section of the strait. Included in this family is a limiting “maximal-exchange” solution with two sections of hydraulic control in the strait and with fixed layer depths at the most constricted section. The state of exchange for a given forcing is predicted using a theory that assumes energy conservation over a certain path connecting the strait to the marginal sea or, in some cases, the ocean. Depending on the configuration of the exchange, long-wave information may be blocked from entering the strait from the marginal sea, from the open ocean, or both. The scenario that holds determines what is predicted and what needs to be input. Numerical tests of the prediction for the temperature difference and the state of exchange are carried out for straits with a pure contraction in width and for a constant width strait with a topographic sill. The comparison is reasonable in most cases, though the numerical model is not able to reproduce cases of multiple states predicted by the theory for certain forcing values. The analytical model is an alternative to the Price and Yang and Siddall et al. models of a marginal sea outflow.
    Beschreibung: This work was supported by the National Science Foundation under Grants OCE-0525729 and OCE-0423975.
    Schlagwort(e): Ocean circulation ; Coastlines ; Ocean models
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  • 56
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    Chaotic advection in an archipelago (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 1988–2006, doi:10.1175/2010JPO4336.1.
    Beschreibung: Techniques from dynamical systems theory have been applied to study horizontal stirring of fluid in the Philippine Archipelago. The authors’ analysis is based on velocity fields produced by two high-resolution (3 and 6 km) numerical models. Particular attention is paid to identifying robust surface flow patterns and associating them with dominant Lagrangian coherent structures (LCSs). A recurrent wind-driven dipole in the lee of the coastline is considered in detail. The associated LCSs form a template for stirring, exchange, and biological transport in and around the dipole. Chaotic advection is argued to provide a relevant framework for interpreting mesoscale horizontal stirring processes in an archipelago as a whole. Implications for the formation of filaments, the production of tracer variance, and the scale at which stirring leads to mixing are discussed in connection with an observed temperature record.
    Beschreibung: This work was supported by the Office of Naval Research: Grant N00014-07-1-0590 to Woods Hole Oceanographic Institution; Grant ONR- 0601153N to Stevens Institute of Technology; Grant N00014-07-1-0417 to Institute of Marine and Coastal Sciences, Rutgers University; and Grant N00014-09-1- 0582 to Lamont-Doherty Earth Observatory of Columbia University.
    Schlagwort(e): Advection ; Ocean circulation
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  • 57
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    Subduction on the northern and southern flanks of the Gulf Stream (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 429-438, doi:10.1175/2009JPO4187.1.
    Beschreibung: Sections of temperature, salinity, dissolved oxygen, and velocity were made crossing the Gulf Stream in late January 2006 to investigate the role of frontal processes in the formation of Eighteen Degree Water (EDW), the Subtropical Mode Water of the North Atlantic. The sections were nominally perpendicular to the stream and measured in a Lagrangian frame by following a floating spar buoy drifting in the Gulf Stream’s warm core. During the survey, EDW was isolated from the mixed layer by the stratified seasonal pycnocline, suggesting that EDW was not yet actively being formed at this time in the season and at the longitudes over which the survey was conducted (64°–70°W). However, in two of the sections, the seasonal pycnocline in the core of the Gulf Stream was broken by an intrusion of cold, fresh, weakly stratified water, nearly saturated in oxygen, that appears to have been subducted from the surface mixed layer north of the stream. The intrusion was identified in three of the sections in profiles with a nearly identical temperature–salinity relation. From the western-to-easternmost sections, where the intrusion was observed, the depth of the intrusion’s salinity minimum descended by 90 m in the 71 h it took to complete this part of the survey. This apparent subduction occurred primarily on the upstream side of a meander trough, where the cross-stream velocity was confluent and frontogenetic. Using a variant of the omega equation, the vertical velocity driven by the confluent flow was inferred and yielded downwelling in the vicinity of the intrusion spanning 10–40 m day−1, a range of values consistent with the intrusion’s observed descent, suggesting that frontal subduction was responsible for the formation of the intrusion. In the easternmost section located downstream of the meander trough, the flow was diffluent, driving an inferred vertical circulation that was of the opposite sense to that in the section upstream of the trough. In transiting the two sides of the trough, the intrusion was observed to move toward the center of the stream between the downwelling branches of the opposing vertical circulations, resulting in a downward Lagrangian mean vertical velocity and net subduction. Hydrographic evidence of the subduction of weakly stratified surface waters was seen in the southern flank of the Gulf Stream as well. The solution of the omega equation suggests that this subduction was associated with a relatively shallow vertical circulation confined to the upper 200 m of the water column in the proximity of the front marking the southern edge of the warm core.
    Beschreibung: Support came from the National Science Foundation Grant OCE-0424865 (TJ and LT). LT was also supported by NSF Grant OCE- 0549699 and the Worzel Assistant Scientist Endowed Fund at WHOI.
    Schlagwort(e): Ocean circulation ; Thermohaline circulation ; Frontogenesis/frontolysis
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  • 58
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    Milankovitch forcing and meridional moisture flux in the atmosphere : insight from a zonally averaged ocean–atmosphere model (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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 Climate 23 (2010): 4841–4855, doi:10.1175/2010JCLI3273.1.
    Beschreibung: A 1-Myr-long time-dependent solution of a zonally averaged ocean–atmosphere model subject to Milankovitch forcing is examined to gain insight into long-term changes in the planetary-scale meridional moisture flux in the atmosphere. The model components are a one-dimensional (latitudinal) atmospheric energy balance model with an active hydrological cycle and an ocean circulation model representing four basins (Atlantic, Indian, Pacific, and Southern Oceans). This study finds that the inclusion of an active hydrological cycle does not significantly modify the responses of annual-mean air and ocean temperatures to Milankovitch forcing found in previous integrations with a fixed hydrological cycle. Likewise, the meridional overturning circulation of the North Atlantic Ocean is not significantly affected by hydrological changes. Rather, it mainly responds to precessionally driven variations of ocean temperature in subsurface layers (between 70- and 500-m depth) of this basin. On the other hand, annual and zonal means of evaporation rate and meridional flux of moisture in the atmosphere respond notably to obliquity-driven changes in the meridional gradient of annual-mean insolation. Thus, when obliquity is decreased (increased), the meridional moisture flux in the atmosphere is intensified (weakened). This hydrological response is consistent with deuterium excess records from polar ice cores, which are characterized by dominant obliquity cycles.
    Beschreibung: A. A. thanks the Global Environmental and Climate Change Centre of McGill University for a Network Grant that made possible an enriching twoweek stay at WHOI during June 2007. O. M. acknowledges support from theU.S.National Science Foundation. Support from a Canadian NSERC Discovery Grant awarded to L.A.M. is gratefully acknowledged.
    Schlagwort(e): Forcing ; Moisture ; Fluxes ; Ocean models ; Coupled models ; Southern Ocean ; Pacific Ocean ; Atlantic Ocean ; Indian Ocean
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    Transport in an idealized three-gyre system with application to the Adriatic Sea (2010)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 675-690, doi:10.1175/2008JPO3975.1.
    Beschreibung: Motivated by observations of surface drifters in the Adriatic Sea, transport in a three-gyre system is studied with the aid of dynamical systems techniques. Particular attention is paid to the issue of intergyre transport. The velocity field is assumed to be two-dimensional and incompressible and composed of a steady three-gyre background flow on which a time-dependent perturbation is superimposed. Two systems of this type are considered: 1) an observationally motivated, analytically prescribed model consisting of a steady background on which a multiperiodic time-dependent perturbation is superimposed, and 2) an observationally based model of the Adriatic Sea consisting of the mean surface circulation derived from surface drifter trajectories on which a time-dependent altimetry-based perturbation velocity field is superimposed. It is shown that for a small perturbation to the steady three-gyre background, two of the gyres exchange no fluid with the third gyre. When the perturbation strength exceeds a certain threshold, transport between all three gyres occurs. This behavior is described theoretically, illustrated using the analytic model and shown to be consistent with the observationally based model of the Adriatic. The relevance of the work presented to more complicated multiple-gyre problems is discussed.
    Beschreibung: This work was supported by the National Science Foundation Grants CMG0417425 and CMG0825547.
    Schlagwort(e): Transport ; Gyres ; Mediterranean region ; Ocean circulation ; Lagrangian circulation
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    An oceanic current against the wind : how does Taiwan island steer warm water into the East China Sea? (2010)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 2563-2569, doi:10.1175/JPO3134.1.
    Beschreibung: Along the Taiwan Strait (〈100 m in depth) a northeastward flow persists in all seasons despite the annually averaged wind stress that is strongly southwestward. The forcing mechanism of this countercurrent is examined by using a simple ocean model. The results from a suite of experiments demonstrate that it is the Kuroshio that plays the deciding role for setting the flow direction along the Taiwan Strait. The momentum balance along the strait is mainly between the wind stress, friction, and pressure gradient. Since both wind stress and friction act against the northward flow, it is most likely the pressure gradient that forces the northward flow, as noted in some previous studies. What remains unknown is why there is a considerable pressure difference between the southern and northern strait. The Kuroshio flows along the east coast of Taiwan, and thus the western boundary current layer dynamics applies there. Integrating the momentum equation along Taiwan’s east coast shows that there must be a pressure difference between the southern and the northern tip of Taiwan to counter a considerable friction exerted by the mighty Kuroshio. This same pressure difference is also felt on the other side of the island where it forces the northward flow through Taiwan Strait. The model shows that the local wind stress acts to dampen this northward flow. This mechanism can be illustrated by an integral constraint for flow around an island.
    Beschreibung: This study has been supported by National Science Foundation through Grant OCE-0351055.
    Schlagwort(e): Ocean circulation ; Wind ; Currents
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  • 61
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    Marine ecosystem dynamics and biogeochemical cycling in the Community Earth System Model [CESM1(BGC)] : comparison of the 1990s with the 2090s under the RCP4.5 and RCP8.5 scenarios (2013)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: 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): 9291–9312, doi:10.1175/JCLI-D-12-00566.1.
    Beschreibung: The authors compare Community Earth System Model results to marine observations for the 1990s and examine climate change impacts on biogeochemistry at the end of the twenty-first century under two future scenarios (Representative Concentration Pathways RCP4.5 and RCP8.5). Late-twentieth-century seasonally varying mixed layer depths are generally within 10 m of observations, with a Southern Ocean shallow bias. Surface nutrient and chlorophyll concentrations exhibit positive biases at low latitudes and negative biases at high latitudes. The volume of the oxygen minimum zones is overestimated. The impacts of climate change on biogeochemistry have similar spatial patterns under RCP4.5 and RCP8.5, but perturbation magnitudes are larger under RCP8.5. Increasing stratification leads to weaker nutrient entrainment and decreased primary and export production (〉30% over large areas). The global-scale decreases in primary and export production scale linearly with the increases in mean sea surface temperature. There are production increases in the high nitrate, low chlorophyll (HNLC) regions, driven by lateral iron inputs from adjacent areas. The increased HNLC export partially compensates for the reductions in non-HNLC waters (~25% offset). Stabilizing greenhouse gas emissions and climate by the end of this century (as in RCP4.5) will minimize the changes to nutrient cycling and primary production in the oceans. In contrast, continued increasing emission of CO2 (as in RCP8.5) will lead to reduced productivity and significant modifications to ocean circulation and biogeochemistry by the end of this century, with more drastic changes beyond the year 2100 as the climate continues to rapidly warm.
    Beschreibung: The CESM project is supported by the National Science Foundation and the Office of Science (BER) of the U.S. Department of Energy. S.C.D. acknowledges support of Collaborative Research: Improved Regional and Decadal Predictions of the Carbon Cycle (NSF AGS-1048827). This work was supported by NSF grants (ARC-0902045 and AGS-1021776 to Moore and AGS- 1048890 to Moore, Lindsay, and Doney).
    Beschreibung: 2014-06-01
    Schlagwort(e): Climate prediction ; Forecast verification/skill ; Climate models ; Ecological models ; Model evaluation/performance ; Ocean models
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    Some dynamical constraints on upstream pathways of the Denmark Strait Overflow (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 3033–3053, doi:10.1175/JPO-D-13-0227.1.
    Beschreibung: The East Greenland Current (EGC) had long been considered the main pathway for the Denmark Strait overflow (DSO). Recent observations, however, indicate that the north Icelandic jet (NIJ), which flows westward along the north coast of Iceland, is a major separate pathway for the DSO. In this study a two-layer numerical model and complementary integral constraints are used to examine various pathways that lead to the DSO and to explore plausible mechanisms for the NIJ’s existence. In these simulations, a westward and NIJ-like current emerges as a robust feature and a main pathway for the Denmark Strait overflow. Its existence can be explained through circulation integrals around advantageous contours. One such constraint spells out the consequences of overflow water as a source of low potential vorticity. A stronger constraint can be added when the outflow occurs through two outlets: it takes the form of a circulation integral around the Iceland–Faroe Ridge. In either case, the direction of overall circulation about the contour can be deduced from the required frictional torques. Some effects of wind stress forcing are also examined. The overall positive curl of the wind forces cyclonic gyres in both layers, enhancing the East Greenland Current. The wind stress forcing weakens but does not eliminate the NIJ. It also modifies the sign of the deep circulation in various subbasins and alters the path by which overflow water is brought to the Faroe Bank Channel, all in ways that bring the idealized model more in line with observations. The sequence of numerical experiments separates the effects of wind and buoyancy forcing and shows how each is important.
    Beschreibung: This study has been supported by National Science Foundation (OCE0927017 and ARC1107412).
    Beschreibung: 2015-06-01
    Schlagwort(e): Circulation/ Dynamics ; Boundary currents ; Channel flows ; Meridional overturning circulation ; Ocean circulation ; Topographic effects
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  • 63
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    Radiocarbon profiles of the NW Pacific from the LGM and deglaciation : evaluating ventilation metrics and the effect of uncertain surface reservoir ages (2015)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 30 (2015): 174–195, doi:10.1002/2014PA002649.
    Beschreibung: During the last deglaciation, the ventilation of the subarctic Pacific is hypothesized to have changed dramatically, including the rejuvenation of a poorly ventilated abyssal water mass that filled the deep ocean, and fluctuations in the strength of North Pacific intermediate and deep water formation at millennial timescales. Foraminiferal radiocarbon reconstructions of past ventilation changes in the Pacific are valuable but are hampered by poor carbonate preservation, low sediment accumulation rates, bias from bioturbation, and poorly constrained past surface reservoir age. In this study, we present paired benthic-planktonic radiocarbon measurements from the Okhotsk Sea and Emperor Seamounts. We take advantage of large contemporaneous peaks in benthic abundances from the last glacial maximum, Bolling-Allerod (BA), and early Holocene to produce time slices of radiocarbon from 1 to 4 km water depth. We explore the impact of uncertain surface reservoir age and evaluate several approaches to quantifying past ocean radiocarbon distribution using our NW Pacific data and a compilation of published data from the North Pacific. Both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age. But for a time slice from a small geographical area with radiocarbon-independent stratigraphic correlation between cores, the shape of a water column profile is independent of surface reservoir age. The NW Pacific profiles are similar in shape to the compilation profiles for the entire North Pacific, which suggests that deglacial surface reservoir age changes across the N Pacific did not diverge dramatically across the areas sampled. The Last Glacial Maximum (LGM) profile 〉2 km spans a wide range of values, ranging from values similar to today to lower than today. However, by the BA the profile has a similar shape to today. Ultimately, local surface reservoir ages, end-member water mass composition, and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes.
    Beschreibung: Support for this project was from NSF grants 0526764, 8312240, and 9912122, and the Williams College Divisional Research Funding Committee. M.S.C. participated in the GAIN writing retreat, which was support by NSF grants 0620101 and 0620087.
    Beschreibung: 2015-09-12
    Schlagwort(e): Deglaciation ; Radiocarbon ; Pacific Ocean ; Ocean circulation
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    Inferring surface water equilibrium calcite δ18O during the last deglacial period from benthic foraminiferal records : implications for ocean circulation (2016)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 30 (2015): 1470-1489, doi:10.1002/2014PA002743.
    Beschreibung: The ocean circulation modifies mixed layer (ML) tracer signals as they are communicated to the deep ocean by advection and mixing. We develop and apply a procedure for using tracer signals observed “upstream” (by planktonic foraminifera) and “downstream” (by benthic foraminifera) to constrain how tracer signals are modified by the intervening circulation and, by extension, to constrain properties of that circulation. A history of ML equilibrium calcite δ18O (δ18Oc) spanning the last deglaciation is inferred from a least-squares fit of eight benthic foraminiferal δ18Oc records to Green's function estimated for the modern ocean circulation. Disagreements between this history and the ML history implied by planktonic records would indicate deviations from the modern circulation. No deviations are diagnosed because the two estimates of ML δ18Oc agree within their uncertainties, but we suggest data collection and modeling procedures useful for inferring circulation changes in future studies. Uncertainties of benthic-derived ML δ18Oc are lowest in the high-latitude regions chiefly responsible for ventilating the deep ocean; additional high-resolution planktonic records constraining these regions are of particular utility. Benthic records from the Southern Ocean, where data are sparse, appear to have the most power to reduce uncertainties in benthic-derived ML δ18Oc. Understanding the spatiotemporal covariance of deglacial ML δ18Oc will also improve abilities of δ18Oc records to constrain deglacial circulation.
    Beschreibung: 2016-05-12
    Schlagwort(e): Oxygen isotopes ; Inverse modeling ; Deglaciation ; Tracers ; Ocean circulation ; Green's function
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    A theory of the wind-driven Beaufort Gyre variability (2016)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 3263-3278, doi:10.1175/JPO-D-16-0091.1.
    Beschreibung: The halocline of the Beaufort Gyre varies significantly on interannual to decadal time scales, affecting the freshwater content (FWC) of the Arctic Ocean. This study explores the role of eddies in the Ekman-driven gyre variability. Following the transformed Eulerian-mean paradigm, the authors develop a theory that links the FWC variability to the stability of the large-scale gyre, defined as the inverse of its equilibration time. The theory, verified with eddy-resolving numerical simulations, demonstrates that the gyre stability is explicitly controlled by the mesoscale eddy diffusivity. An accurate representation of the halocline dynamics requires the eddy diffusivity of 300 ± 200 m2 s−1, which is lower than what is used in most low-resolution climate models. In particular, on interannual and longer time scales the eddy fluxes and the Ekman pumping provide equally important contributions to the FWC variability. However, only large-scale Ekman pumping patterns can significantly alter the FWC, with spatially localized perturbations being an order of magnitude less efficient. Lastly, the authors introduce a novel FWC tendency diagnostic—the Gyre Index—that can be conveniently calculated using observations located only along the gyre boundaries. Its strong predictive capabilities, assessed in the eddy-resolving model forced by stochastic winds, suggest that the Gyre Index would be of use in interpreting FWC evolution in observations as well as in numerical models.
    Beschreibung: GEMacknowledges the support from theHowland Postdoctoral Program Fund at WHOI and the Stanback Fellowship Fund at Caltech.MAS was supported by NSF Grants PLR-1415489 and OCE-1232389. AFT acknowledges support from NASA Award NNN12AA01C.
    Beschreibung: 2017-04-20
    Schlagwort(e): Arctic ; Eddies ; Ekman pumping/transport ; Large-scale motions ; Ocean circulation ; Stability
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    A global glacial ocean state estimate constrained by upper-ocean temperature proxies (2018)
    American Meteorological Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 8059-8079, doi:10.1175/JCLI-D-17-0769.1.
    Beschreibung: We use the method of least squares with Lagrange multipliers to fit an ocean general circulation model to the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) estimate of near sea surface temperature (NSST) at the Last Glacial Maximum (LGM; circa 23–19 thousand years ago). Compared to a modern simulation, the resulting global, last-glacial ocean state estimate, which fits the MARGO data within uncertainties in a free-running coupled ocean–sea ice simulation, has global-mean NSSTs that are 2°C lower and greater sea ice extent in all seasons in both the Northern and Southern Hemispheres. Increased brine rejection by sea ice formation in the Southern Ocean contributes to a stronger abyssal stratification set principally by salinity, qualitatively consistent with pore fluid measurements. The upper cell of the glacial Atlantic overturning circulation is deeper and stronger. Dye release experiments show similar distributions of Southern Ocean source waters in the glacial and modern western Atlantic, suggesting that LGM NSST data do not require a major reorganization of abyssal water masses. Outstanding challenges in reconstructing LGM ocean conditions include reducing effects from model biases and finding computationally efficient ways to incorporate abyssal tracers in global circulation inversions. Progress will be aided by the development of coupled ocean–atmosphere–ice inverse models, by improving high-latitude model processes that connect the upper and abyssal oceans, and by the collection of additional paleoclimate observations.
    Beschreibung: DEA was supported by a NSF Graduate Research Fellowship and NSF Grant OCE-1060735. OM acknowledges support from the NSF. GF was supported by NASA Award 1553749 and Simons Foundation Award 549931.
    Schlagwort(e): Ocean ; Abyssal circulation ; Sea surface temperature ; Paleoclimate ; Inverse methods ; Ocean models
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    Structure and forcing of observed exchanges across the Greenland–Scotland Ridge (2018)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 31 (2018): 9881-9901, doi:10.1175/JCLI-D-17-0889.1.
    Beschreibung: The Atlantic meridional overturning circulation and associated poleward heat transport are balanced by northern heat loss to the atmosphere and corresponding water-mass transformation. The circulation of northward-flowing Atlantic Water at the surface and returning overflow water at depth is particularly manifested—and observed—at the Greenland–Scotland Ridge where the water masses are guided through narrow straits. There is, however, a rich variability in the exchange of water masses across the ridge on all time scales. Focusing on seasonal and interannual time scales, and particularly the gateways of the Denmark Strait and between the Faroe Islands and Shetland, we specifically assess to what extent the exchanges of water masses across the Greenland–Scotland Ridge relate to wind forcing. On seasonal time scales, the variance explained of the observed exchanges can largely be related to large-scale wind patterns, and a conceptual model shows how this wind forcing can manifest via a barotropic, cyclonic circulation. On interannual time scales, the wind stress impact is less direct as baroclinic mechanisms gain importance and observations indicate a shift in the overflows from being more barotropically to more baroclinically forced during the observation period. Overall, the observed Greenland–Scotland Ridge exchanges reflect a horizontal (cyclonic) circulation on seasonal time scales, while the interannual variability more represents an overturning circulation.
    Beschreibung: This research was supported by the Research Council of Norway project NORTH (Grant 229763). Additional support for M. A. Spall was provided by National Science Foundation Grant OCE- 1558742, for T. Eldevik and S. Østerhus by the European Union’s Horizon 2020 research and innovation program project Blue-Action (Grant 727852), and for S. Østerhus by the European Framework Programs under Grant Agreement 308299 (NACLIM).
    Schlagwort(e): Ocean circulation ; Thermocline circulation ; Atmosphere-ocean interaction ; North Atlantic Oscillation ; Statistical techniques ; Time series
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  • 68
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    2008 program of studies : perspectives and challenges in GFD (2009)
    Woods Hole Oceanographic Institution
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: The GFD Program in 2008 ran with a special theme, in view of the 50th anniversary of the beginning of the program. The first two weeks of Principal Lectures dealt with "Perspectives and Challenges" of the subject, and we commemorated by having ten different lecturers with a diversity of viewpoints and opinions. Though the lectures thereby took less of a pedagogical flavour, each afternoon we saw the fellows grill the lecturers in informal afternoon tutorials. Also by way of celebration, the Oceanographic Institution threw a 50th anniversary party in honour of the Program and the "Founding Fathers." This was held on one of the lawns in front of Walsh Cottage on Friday, June 27th. We saw a variety of familiar faces, some from the very first years of the Program, others from more recent summers. George Veronis and Jack Whitehead read short pieces about the past fifty years, including the unveiling of the "2008 AGU Award for Excellence in Geophysical Education" awarded to the Program by the American Geophysical Union. The party was skillfully organized by Janet Fields and uniformly enjoyed by all. In 2008 the Sears Public Lecture was delivered by Andy Ingersoll (CalTech) and entitled "Weather and Climates of Other Worlds: Lessons for Earth." Andy, a participant of the program for many years, described the insights that could be drawn regarding our own climate from observing those of the other planets in the solar system, observations made particularly clear and compelling by recent space missions. Over a hundred people gathered at Redfield for the lecture, many of whom paused afterwards to enjoy conversation and refreshments at the reception that followed. Other novelties at the 2008 program included Bill Dewar's delivery of a seminar at Walsh in full Scottish regalia, kilt and all. Last, and of course most importantly, we had an industrious group of fellows who rose to the challenge of the Program and contributed tremendously to the anniversary. As always, the WHOI Academic Programs Office and the Physical Oceanography Department provided the administrative backbone to the summer, and Walsh Cottage was perfectly unchanged in its intimacy and rustic atmosphere. Jeanne Fleming, Penny Foster and Janet Fields contributed importantly to the smooth running of the program.
    Beschreibung: Funding was provided by the National Science Foundation under grant OCE-0325296 and by the Office of Naval Research, Processes and Prediction Division, Physical Oceanography Program under grant N00014-07-10776
    Schlagwort(e): Boundary layer ; Ocean circulation
    Repository-Name: Woods Hole Open Access Server
    Materialart: Technical Report
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    2009 program of studies : nonlinear waves (2010)
    Woods Hole Oceanographic Institution
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: The fiftieth year of the program was dedicated to Nonlinear Waves, a topic with many applications in geophysical fluid dynamics. The principal lectures were given jointly by Roger Grimshaw and Harvey Segur and between them they covered material drawn from fundamental theory, fluid experiments, asymptotics, and reaching all the way to detailed applications. These lectures set the scene for the rest of the summer, with subsequent daily lectures by staff and visitors on a wide range of topics in GFD. It was a challenge for the fellows and lecturers to provide a consistent set of lecture notes for such a wide-ranging lecture course, but not least due to the valiant efforts of Pascale Garaud, who coordinated the write-up and proof-read all the notes, we are very pleased with the final outcome contained in these pages. This year’s group of eleven international GFD fellows was as diverse as one could get in terms of gender, origin, and race, but all were unified in their desire to apply their fundamental knowledge of fluid dynamics to challenging problems in the real world. Their projects covered a huge range of physical topics and at the end of the summer each student presented his or her work in a one-hour lecture. As always, these projects are the heart of the research and education aspects of our summer study.
    Beschreibung: Funding was provided by the National Science Foundation through Grant No. OCE-0824636 and the Office of Naval Research under Contract No. N00014-09-10844.
    Schlagwort(e): Ocean waves ; Ocean circulation
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  • 70
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    An enhancement of low-frequency variability in the Kuroshio–Oyashio Extension in CCSM3 owing to ocean model biases (2011)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: 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 Climate 23 (2010): 6221–6233, doi:10.1175/2010JCLI3402.1.
    Beschreibung: Enhanced decadal variability in sea surface temperature (SST) centered on the Kuroshio Extension (KE) has been found in the Community Climate System Model version 3 (CCSM3) as well as in other coupled climate models. This decadal peak has higher energy than is found in nature, almost twice as large in some cases. While previous analyses have concentrated on the mechanisms for such decadal variability in coupled models, an analysis of the causes of excessive SST response to changes in wind stress has been missing. Here, a detailed comparison of the relationships between interannual changes in SST and sea surface height (SSH) as a proxy for geostrophic surface currents in the region in both CCSM3 and observations, and how these relationships depend on the mean ocean circulation, temperature, and salinity, is made. We use observationally based climatological temperature and salinity fields as well as satellite-based SSH and SST fields for comparison. The primary cause for the excessive SST variability is the coincidence of the mean KE with the region of largest SST gradients in the model. In observations, these two regions are separated by almost 500 km. In addition, the too shallow surface oceanic mixed layer in March north of the KE in the subarctic Pacific contributes to the biases. These biases are not unique to CCSM3 and suggest that mean biases in current, temperature, and salinity structures in separated western boundary current regions can exert a large influence on the size of modeled decadal SST variability.
    Beschreibung: Support for L.T. was provided by the NASA sponsored Ocean Surface Topography Science Team, under Contract 1267196 with the University of Washington, administered by the Jet Propulsion Laboratory. Support for Y.-O. K. comes from the NOAA Office of Global Programs (grant to C. Deser and Y.-O. Kwon) and the WHOI Heyman fellowship.
    Schlagwort(e): Bias ; Coupled models ; Decadal variability ; Ocean models ; Sea surface temperature ; Wind stress
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    The mean age of ocean waters inferred from radiocarbon observations : sensitivity to surface sources and accounting for mixing histories (2012)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: 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): 291–305, doi:10.1175/JPO-D-11-043.1.
    Beschreibung: A number of previous observational studies have found that the waters of the deep Pacific Ocean have an age, or elapsed time since contact with the surface, of 700–1000 yr. Numerical models suggest ages twice as old. Here, the authors present an inverse framework to determine the mean age and its upper and lower bounds given Global Ocean Data Analysis Project (GLODAP) radiocarbon observations, and they show that the potential range of ages increases with the number of constituents or sources that are included in the analysis. The inversion requires decomposing the World Ocean into source waters, which is obtained here using the total matrix intercomparison (TMI) method at up to 2° × 2° horizontal resolution with 11 113 surface sources. The authors find that the North Pacific at 2500-m depth can be no younger than 1100 yr old, which is older than some previous observational estimates. Accounting for the broadness of surface regions where waters originate leads to a reservoir-age correction of almost 100 yr smaller than would be estimated with a two or three water-mass decomposition and explains some of the discrepancy with previous observational studies. A best estimate of mean age is also presented using the mixing history along circulation pathways. Subject to the caveats that inference of the mixing history would benefit from further observations and that radiocarbon cannot rule out the presence of extremely old waters from exotic sources, the deep North Pacific waters are 1200–1500 yr old, which is more in line with existing numerical model results.
    Beschreibung: GG is supported by the J. Lamar Worzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists. PJH is supported by NSF Award 0960787.
    Beschreibung: 2012-08-01
    Schlagwort(e): North Pacific Ocean ; Mass fluxes/transport ; Ocean circulation ; Tracers ; Optimization ; Variational analysis
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  • 72
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    Modeling and analysis of internal-tide generation and beamlike onshore propagation in the vicinity of shelfbreak canyons (2014)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 834-849, doi:10.1175/JPO-D-13-0179.1.
    Beschreibung: A hydrostatic numerical model with alongshore-uniform barotropic M2 tidal boundary forcing and idealized shelfbreak canyon bathymetries is used to study internal-tide generation and onshore propagation. A control simulation with Mid-Atlantic Bight representative bathymetry is supported by other simulations that serve to identify specific processes. The canyons and adjacent slopes are transcritical in steepness with respect to M2 internal wave characteristics. Although the various canyons are symmetrical in structure, barotropic-to-baroclinic energy conversion rates Cυ are typically asymmetrical within them. The resulting onshore-propagating internal waves are the strongest along beams in the horizontal plane, with the stronger beam in the control simulation lying on the side with higher Cυ. Analysis of the simulation results suggests that the cross-canyon asymmetrical Cυ distributions are caused by multiple-scattering effects on one canyon side slope, because the phase variation in the spatially distributed internal-tide sources, governed by variations in the orientation of the bathymetry gradient vector, allows resonant internal-tide generation. A less complex, semianalytical, modal internal wave propagation model with sources placed along the critical-slope locus (where the M2 internal wave characteristic is tangent to the seabed) and variable source phasing is used to diagnose the physics of the horizontal beams of onshore internal wave radiation. Model analysis explains how the cross-canyon phase and amplitude variations in the locally generated internal tides affect parameters of the internal-tide beams. Under the assumption that strong internal tides on continental shelves evolve to include nonlinear wave trains, the asymmetrical internal-tide generation and beam radiation effects may lead to nonlinear internal waves and enhanced mixing occurring preferentially on one side of shelfbreak canyons, in the absence of other influencing factors.
    Beschreibung: All three authors were supported by Office of Naval Research (ONR) Grant N00014-11-1-0701. WGZ was additionally supported by the National Science Foundation (NSF) Grant OCE-1154575, and TFD was additionally supported by NSF Grant OCE-1060430.
    Beschreibung: 2014-09-01
    Schlagwort(e): Circulation/ Dynamics ; Baroclinic flows ; Internal waves ; Ocean circulation ; Topographic effects ; Waves, oceanic ; Models and modeling ; Numerical analysis/modeling
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  • 73
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    Direct estimate of lateral eddy diffusivity upstream of Drake Passage (2014)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 2593–2616, doi:10.1175/JPO-D-13-0120.1.
    Beschreibung: The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The meridional eddy diffusivity, a measure of the rate at which the area of the tracer spreads along an isopycnal across the Antarctic Circumpolar Current, is 710 ± 260 m2 s−1 at 1500-m depth. The estimate is based on an extrapolation of the tracer-based diffusivity using output from numerical tracers released in a one-twentieth of a degree model simulation of the circulation and turbulence in the Drake Passage region. The model is shown to reproduce the observed spreading rate of the DIMES tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s−1 and peaks at the steering level, near 2 km, where the eddy phase speed is equal to the mean flow speed. These vertical variations are not captured by ocean models presently used for climate studies, but they significantly affect the ventilation of different water masses.
    Beschreibung: NSF support through Awards OCE-1233832, OCE-1232962, and OCE-1048926 is gratefully acknowledged.
    Beschreibung: 2015-04-01
    Schlagwort(e): Geographic location/entity ; Southern Ocean ; Circulation/ Dynamics ; Diffusion ; Eddies ; Ocean circulation ; Turbulence ; Physical Meteorology and Climatology ; Isopycnal mixing
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  • 74
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    Eddy–wind interaction in the California Current System : dynamics and impacts (2016)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 439-459, doi:10.1175/JPO-D-15-0086.1.
    Beschreibung: The summertime California Current System (CCS) is characterized by energetic mesoscale eddies, whose sea surface temperature (SST) and surface current can significantly modify the wind stress and Ekman pumping. Relative importance of the eddy–wind interactions via SST and surface current in the CCS is examined using a high-resolution (7 km) regional coupled model with a novel coupling approach to isolate the small-scale air–sea coupling by SST and surface current. Results show that when the eddy-induced surface current is allowed to modify the wind stress, the spatially averaged surface eddy kinetic energy (EKE) is reduced by 42%, and this is primarily due to enhanced surface eddy drag and reduced wind energy transfer. In contrast, the eddy-induced SST–wind coupling has no significant impact on the EKE. Furthermore, eddy-induced SST and surface current modify the Ekman pumping via their crosswind SST gradient and surface vorticity gradient, respectively. The resultant magnitudes of the Ekman pumping velocity are comparable, but the implied feedback effects on the eddy statistics are different. The surface current-induced Ekman pumping mainly attenuates the amplitude of cyclonic and anticyclonic eddies, acting to reduce the eddy activity, while the SST-induced Ekman pumping primarily affects the propagation. Time mean–rectified change in SST is determined by the altered offshore temperature advection by the mean and eddy currents, but the magnitude of the mean SST change is greater with the eddy-induced current effect. The demonstrated remarkably strong dynamical response in the CCS system to the eddy-induced current–wind coupling indicates that eddy-induced current should play an important role in the regional coupled ocean–atmosphere system.
    Beschreibung: We thank NSF for support under GrantsOCE-0960770,OCE-1419235, andOCE-1419306. HS is grateful for the WHOI internal support from the Andrew W. Mellon Foundation Awards for Innovative Research and the additional support from the ONR We thank NSF for support under GrantsOCE-0960770,OCE-1419235, andOCE-1419306. HS is grateful for the WHOI internal support from the Andrew W. Mellon Foundation Awards for Innovative Research and the additional support from the ONR
    Beschreibung: 2016-05-30
    Schlagwort(e): Atm/Ocean Structure/ Phenomena ; Atmosphere-ocean interaction ; Ekman pumping ; Models and modeling ; Ocean models ; Regional models
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    The Deep Water Dispersion Experiment: RAFOS float data report June 2016 - January 2019 (2020)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-12-01
    Beschreibung: This is the final data report for all acoustically-tracked subsurface RAFOS floats deployed for the “Deep Water Dispersion Experiment: RAFOS Float Study in Support of Analysis of Possible Consequences of Large Scale Oil-Spills under Various Scenarios” (DWDE). This study is part of the larger program “Deep and Shallow Particle Dispersion and Biological Connectivity over the Continental Slope in the Western Gulf of Mexico”, of the Gulf of Mexico Research Consortium (CIGoM). The objective of the DWDE project was to measure and evaluate the ocean circulation at various depths in order to estimate the rates and pathways by which a passive tracer (e.g. pollutant, nutrients, etc.) would spread. The experiment consisted of the deployment 93 RAFOS floats and five sound source moorings (needed for tracking the floats underwater) over the course of five cruises, between June 2016 and January 2019, in the Perdido region of the Gulf of Mexico. The floats were deployed nearly simultaneously at stacked depths of 300 and 1500 dbar, in sets of 2-4 instruments per station, for calculating dispersion statistics. Mission lengths for the floats were set to ~12 to 18 months. Included in this report are cruise summaries, statistics and notes on sound source and float performance, sound source drift calculations, description of the RAFOS float data processing steps, and figures.
    Beschreibung: Funding was provided by the Mexican National Council for Science and Technology - Mexican Ministry of Energy - Hydrocarbon Fund, project 201441. This work was completed through a contract by the Center for Scientific Research and Higher Education at Ensenada (CICESE) under Grant No. 188355 to the Woods Hole Oceanographic Institution.
    Schlagwort(e): RAFOS ; Trajectory ; Gulf of Mexico ; Deep Water Dispersion Experiment ; Ocean circulation
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    Materialart: Technical Report
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    A time-dependent Sverdrup relation and its application to the Indian Ocean (2022)
    American Meteorological Society
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    Publikationsdatum: 2022-11-27
    Beschreibung: Author Posting. © American Meteorological Society, 2022. 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 52(6), (2022): 1233-1244, https://doi.org/10.1175/jpo-d-21-0223.1.
    Beschreibung: The Sverdrup relation is the backbone of wind-driven circulation theory; it is a simple relation between the meridional transport of the wind-driven circulation in the upper ocean and the wind stress curl. However, the relation is valid for steady circulation only. In this study, a time-dependent Sverdrup relation is postulated, in which the meridional transport in a time-dependent circulation is the sum of the local wind stress curl term and a time-delayed term representing the effect of the eastern boundary condition. As an example, this time-dependent Sverdrup relation is evaluated through its application to the equatorial circulation in the Indian Ocean, using reanalysis data and a reduced gravity model. Close examination reveals that the southward Somali Current occurring during boreal winter is due to the combination of the local wind stress curl in the Arabian Sea and delayed signals representing the time change of layer thickness at the eastern boundary.
    Beschreibung: This work is supported by NSFC (41822602, 41976016, 42005035, 42076021), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB42000000, XDA 20060502), Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0306), Guangdong Basic and Applied Basic Research Foundation (2021A1515011534), Youth Innovation Promotion Association CAS, ISEE2021ZD01, and LTOZZ2002. The numerical simulation is supported by the High-Performance Computing Division in the South China Sea Institute of Oceanology.
    Beschreibung: 2022-11-27
    Schlagwort(e): Ocean circulation ; Ocean dynamics ; Rossby waves ; Wind stress curl
    Repository-Name: Woods Hole Open Access Server
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  • 77
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    Deep-current intraseasonal variability interpreted as topographic Rossby waves and deep eddies in the Xisha Islands of the South China Sea (2022)
    American Meteorological Society
    Details
    Publikationsdatum: 2022-12-16
    Beschreibung: Author Posting. © American Meteorological Society, 2022. 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 52(7), (2022): 1415–1430. https://doi.org/10.1175/JPO-D-21-0147.1.
    Beschreibung: Strong subinertial variability near a seamount at the Xisha Islands in the South China Sea was revealed by mooring observations from January 2017 to January 2018. The intraseasonal deep flows presented two significant frequency bands, with periods of 9–20 and 30–120 days, corresponding to topographic Rossby waves (TRWs) and deep eddies, respectively. The TRW and deep eddy signals explained approximately 60% of the kinetic energy of the deep subinertial currents. The TRWs at the Ma, Mb, and Mc moorings had 297, 262, and 274 m vertical trapping lengths, and ∼43, 38, and 55 km wavelengths, respectively. Deep eddies were independent from the upper layer, with the largest temperature anomaly being 〉0.4°C. The generation of the TRWs was induced by mesoscale perturbations in the upper layer. The interaction between the cyclonic–anticyclonic eddy pair and the seamount topography contributed to the generation of deep eddies. Owing to the potential vorticity conservation, the westward-propagating tilted interface across the eddy pair squeezed the deep-water column, thereby giving rise to negative vorticity west of the seamount. The strong front between the eddy pair induced a northward deep flow, thereby generating a strong horizontal velocity shear because of lateral friction and enhanced negative vorticity. Approximately 4 years of observations further confirmed the high occurrence of TRWs and deep eddies. TRWs and deep eddies might be crucial for deep mixing near rough topographies by transferring mesoscale energy to small scales.
    Beschreibung: This work was supported by the National Natural Science Foundation of China (92158204, 91958202, 42076019, 41776036, 91858203), the Open Project Program of State Key Laboratory of Tropical Oceanography (project LTOZZ2001), and Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0304).
    Beschreibung: 2022-12-16
    Schlagwort(e): Abyssal circulation ; Ocean circulation ; Ocean dynamics ; Intraseasonal variability
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    Using the Helmholtz decomposition to define the Indian Ocean meridional overturning streamfunction (2020)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2020. 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 50(3), (2020): 679-694, doi:10.1175/JPO-D-19-0218.1.
    Beschreibung: The zonally integrated flow in a basin can be separated into the divergent/nondivergent parts, and a uniquely defined meridional overturning circulation (MOC) can be calculated. For a basin with significant volume exchange at zonal open boundaries, this method is competent in removing the components associated with the nonzero source terms due to zonal transports at open boundaries. This method was applied to the zonally integrated flow in the Indian Ocean basin extended all the way to the Antarctic by virtue of the ECCO dataset. The contributions due to two major zonal flow systems at open boundaries, the Indonesian Throughflow (ITF) and the Antarctic Circumpolar Current (ACC), were well separated from the rotational flow component, and a nondivergent overturning circulation pattern was identified. Comparisons with previous studies on the MOC of the Indian Ocean in different seasons showed overall consistency but with refinements in details to the south of the entry of the ITF, reflecting the influence of ITF on the MOC pattern in the domain. Other options of decomposition are also examined.
    Beschreibung: LH was supported by the National Basic Research Program of China through Grant 2019YFA0606703 and “The Fundamental Research Funds of Shandong University” (2019GN051). The authors thank the anonymous reviewers and the editor for their constructive comments. Code availability: The Matlab code that performs the decomposition and produces some figures in this paper is available at https://github.com/lei-han-SDU/IMOC/.
    Beschreibung: 2020-09-02
    Schlagwort(e): Meridional overturning circulation ; Ocean circulation ; Streamfunction
    Repository-Name: Woods Hole Open Access Server
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  • 79
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    Potential vorticity dynamics of the arctic halocline (2021)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2020. 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 50(9), (2020): 2491-2506, doi:10.1175/JPO-D-20-0056.1.
    Beschreibung: An idealized two-layer shallow water model is applied to the study of the dynamics of the Arctic Ocean halocline. The model is forced by a surface stress distribution reflective of the observed wind stress pattern and ice motion and by an inflow representing the flow of Pacific Water through Bering Strait. The model reproduces the main elements of the halocline circulation: an anticyclonic Beaufort Gyre in the western basin (representing the Canada Basin), a cyclonic circulation in the eastern basin (representing the Eurasian Basin), and a Transpolar Drift between the two gyres directed from the upwind side of the basin to the downwind side of the basin. Analysis of the potential vorticity budget shows a basin-averaged balance primarily between potential vorticity input at the surface and dissipation at the lateral boundaries. However, advection is a leading-order term not only within the anticyclonic and cyclonic gyres but also between the gyres. This means that the eastern and western basins are dynamically connected through the advection of potential vorticity. Both eddy and mean fluxes play a role in connecting the regions of potential vorticity input at the surface with the opposite gyre and with the viscous boundary layers. These conclusions are based on a series of model runs in which forcing, topography, straits, and the Coriolis parameter were varied.
    Beschreibung: This study was supported by National Science Foundation Grant OPP-1822334. Comments and suggestions from two anonymous referees greatly helped to improve the paper.
    Beschreibung: 2021-02-17
    Schlagwort(e): Eddies ; Ekman pumping/transport ; Ocean circulation ; Ocean dynamics ; Potential vorticity ; Shallow-water equations
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    Assessment of numerical simulations of deep circulation and variability in the Gulf of Mexico using recent observations (2020)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2020. 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 50(4), (2020): 1045-1064, doi:10.1175/JPO-D-19-0137.1.
    Beschreibung: Three simulations of the circulation in the Gulf of Mexico (the “Gulf”) using different numerical general circulation models are compared with results of recent large-scale observational campaigns conducted throughout the deep (〉1500 m) Gulf. Analyses of these observations have provided new understanding of large-scale mean circulation features and variability throughout the deep Gulf. Important features include cyclonic flow along the continental slope, deep cyclonic circulation in the western Gulf, a counterrotating pair of cells under the Loop Current region, and a cyclonic cell to the south of this pair. These dominant circulation features are represented in each of the ocean model simulations, although with some obvious differences. A striking difference between all the models and the observations is that the simulated deep eddy kinetic energy under the Loop Current region is generally less than one-half of that computed from observations. A multidecadal integration of one of these numerical simulations is used to evaluate the uncertainty of estimates of velocity statistics in the deep Gulf computed from limited-length (4 years) observational or model records. This analysis shows that the main deep circulation features identified from the observational studies appear to be robust and are not substantially impacted by variability on time scales longer than the observational records. Differences in strengths and structures of the circulation features are identified, however, and quantified through standard error analysis of the statistical estimates using the model solutions.
    Beschreibung: This work was supported by the Gulf Research Program of the National Academy of Sciences under Awards 2000006422 and 2000009966. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program or the National Academy of Sciences. The authors acknowledge the GLORYS project for providing the ocean reanalysis data used in the ROMS simulation. GLORYS is jointly conducted by MERCATOR OCEAN, CORIOLIS, and CNRS/INSU. Installation, recovery, data acquisition, and processing of the CANEK group current-meter moorings were possible because of CICESE-PetróleosMexicanos Grant PEP-CICESE 428229851 and the dedicated work of the crew of the B/O Justo Sierra and scientists of the CANEK group. The authors thank Dr. Aljaz Maslo, CICESE, for assistance with analysis of model data. The Bureau of Ocean Energy Management (BOEM), U.S. Dept. of the Interior, provided funding for the Lagrangian Study of the Deep Circulation in the Gulf of Mexico and the Observations and Dynamics of the Loop Current study. HYCOM simulation data are available from the HYCOM data server (https://www.hycom.org/data/goml0pt04/expt-02pt2), MITgcm data are available from the ECCO data server (http://ecco.ucsd.edu/gom_results2.html), and the ROMS simulation data are available from GRIIDC (NA.x837.000:0001).
    Schlagwort(e): Ocean circulation ; Abyssal circulation ; Bottom currents/bottom water ; Eddies ; Ocean models
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  • 81
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    Kinematic structure and dynamics of the Denmark Strait Overflow from ship-based observations (2021)
    American Meteorological Society
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    Publikationsdatum: 2022-05-27
    Beschreibung: Author Posting. © American Meteorological Society, 2020. 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 50(11), (2020): 3235–3251, https://doi.org/10.1175/JPO-D-20-0095.1.
    Beschreibung: The dense outflow through Denmark Strait is the largest contributor to the lower limb of the Atlantic meridional overturning circulation, yet a description of the full velocity field across the strait remains incomplete. Here we analyze a set of 22 shipboard hydrographic–velocity sections occupied along the Látrabjarg transect at the Denmark Strait sill, obtained over the time period 1993–2018. The sections provide the first complete view of the kinematic components at the sill: the shelfbreak East Greenland Current (EGC), the combined flow of the separated EGC, and the North Icelandic Jet (NIJ), and the northward-flowing North Icelandic Irminger Current (NIIC). The total mean transport of overflow water is 3.54 ± 0.29 Sv (1 Sv ≡ 106 m3 s−1), comparable to previous estimates. The dense overflow is partitioned in terms of water mass constituents and flow components. The mean transports of the two types of overflow water—Atlantic-origin Overflow Water and Arctic-origin Overflow Water—are comparable in Denmark Strait, while the merged NIJ–separated EGC transports 55% more water than the shelfbreak EGC. A significant degree of water mass exchange takes place between the branches as they converge in Denmark Strait. There are two dominant time-varying configurations of the flow that are characterized as a cyclonic state and a noncyclonic state. These appear to be wind-driven. A potential vorticity analysis indicates that the flow through Denmark Strait is subject to symmetric instability. This occurs at the top of the overflow layer, implying that the mixing/entrainment process that modifies the overflow water begins at the sill.
    Beschreibung: Funding for the study was provided by National Science Foundation (NSF) Grants OCE-1259618, OCE-1756361, and OCE-1558742. The German research cruises were financially supported through various EU Projects (e.g. THOR, NACLIM) and national projects (most recently TRR 181 “Energy Transfer in Atmosphere and Ocean” funded by the German Research Foundation and RACE II “Regional Atlantic Circulation and Global Change” funded by the German Federal Ministry for Education and Research). GWKM acknowledges the support of the Natural Sciences and Engineering Research Council of Canada. LP was supported by NSF Grant OCE-1657870.
    Schlagwort(e): Currents ; Instability ; Ocean circulation ; Ocean dynamics ; Potential vorticity
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  • 82
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    How much Arctic fresh water participates in the subpolar overturning circulation? (2021)
    American Meteorological Society
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    Publikationsdatum: 2022-05-27
    Beschreibung: Author Posting. © American Meteorological Society, 2021. 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 51(3), (2021): 955–973, https://doi.org/10.1175/JPO-D-20-0240.1.
    Beschreibung: Fresh Arctic waters flowing into the Atlantic are thought to have two primary fates. They may be mixed into the deep ocean as part of the overturning circulation, or flow alongside regions of deep water formation without impacting overturning. Climate models suggest that as increasing amounts of freshwater enter the Atlantic, the overturning circulation will be disrupted, yet we lack an understanding of how much freshwater is mixed into the overturning circulation’s deep limb in the present day. To constrain these freshwater pathways, we build steady-state volume, salt, and heat budgets east of Greenland that are initialized with observations and closed using inverse methods. Freshwater sources are split into oceanic Polar Waters from the Arctic and surface freshwater fluxes, which include net precipitation, runoff, and ice melt, to examine how they imprint the circulation differently. We find that 65 mSv (1 Sv ≡ 106 m3 s−1) of the total 110 mSv of surface freshwater fluxes that enter our domain participate in the overturning circulation, as do 0.6 Sv of the total 1.2 Sv of Polar Waters that flow through Fram Strait. Based on these results, we hypothesize that the overturning circulation is more sensitive to future changes in Arctic freshwater outflow and precipitation, while Greenland runoff and iceberg melt are more likely to stay along the coast of Greenland.
    Beschreibung: We gratefully acknowledge the U.S. National Science Foundation: this work was supported by Grants OCE-1258823, OCE-1756272, OCE-1948335, and OCE-2038481. L.H.S. thanks the U.S. Norway Fulbright Foundation for the Norwegian Arctic Chair Grant 2019-20 that made the visit to Scripps Institution of Oceanography possible. N.P.H. acknowledges support by the U.K. Natural Environment Research Council (NERC) National Capability program CLASS (NE/R015953/1), and Grants U.K.-OSNAP (NE/K010875/1, NE/K010875/2) and U.K.-OSNAP Decade (NE/T00858X/1). We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modelling, coordinated and promoted CMIP6.
    Schlagwort(e): Arctic ; North Atlantic Ocean ; Conservation equations ; Meridional overturning circulation ; Ocean circulation ; Inverse methods
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  • 83
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    Kinetic energy transfers between mesoscale and submesoscale motions in the open ocean’s upper layers (2022)
    American Meteorological Society
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    Publikationsdatum: 2022-09-15
    Beschreibung: Author Posting. © American Meteorological Society, 2022. 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 52(1),(2022): 75–97, https://doi.org/10.1175/JPO-D-21-0099.1.
    Beschreibung: Mesoscale eddies contain the bulk of the ocean’s kinetic energy (KE), but fundamental questions remain on the cross-scale KE transfers linking eddy generation and dissipation. The role of submesoscale flows represents the key point of discussion, with contrasting views of submesoscales as either a source or a sink of mesoscale KE. Here, the first observational assessment of the annual cycle of the KE transfer between mesoscale and submesoscale motions is performed in the upper layers of a typical open-ocean region. Although these diagnostics have marginal statistical significance and should be regarded cautiously, they are physically plausible and can provide a valuable benchmark for model evaluation. The cross-scale KE transfer exhibits two distinct stages, whereby submesoscales energize mesoscales in winter and drain mesoscales in spring. Despite this seasonal reversal, an inverse KE cascade operates throughout the year across much of the mesoscale range. Our results are not incompatible with recent modeling investigations that place the headwaters of the inverse KE cascade at the submesoscale, and that rationalize the seasonality of mesoscale KE as an inverse cascade-mediated response to the generation of submesoscales in winter. However, our findings may challenge those investigations by suggesting that, in spring, a downscale KE transfer could dampen the inverse KE cascade. An exploratory appraisal of the dynamics governing mesoscale–submesoscale KE exchanges suggests that the upscale KE transfer in winter is underpinned by mixed layer baroclinic instabilities, and that the downscale KE transfer in spring is associated with frontogenesis. Current submesoscale-permitting ocean models may substantially understate this downscale KE transfer, due to the models’ muted representation of frontogenesis.
    Beschreibung: The OSMOSIS experiment was funded by the U.K. Natural Environment Research Council (NERC) through Grants NE/1019999/1 and NE/101993X/1. ACNG acknowledges the support of the Royal Society and the Wolfson Foundation, and XY that of a China Scholarship Council PhD studentship.
    Schlagwort(e): Ageostrophic circulations ; Dynamics ; Eddies ; Energy transport ; Frontogenesis/frontolysis ; Instability ; Mesoscale processes ; Nonlinear dynamics ; Ocean circulation ; Ocean dynamics ; Small scale processes ; Turbulence
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  • 84
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    2007 program of studies : boundary layers (2008)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: The topic of the Principal Lectures for the forty-ninth year of the program was “Boundary Layers”. The subject centers around those problems in which the boundary conditions lead to a large gradient near the boundary. Nine of this year’s principal lectures were given by Joe Pedlosky and the tenth was given by Steve Lentz. The fluid mechanics of boundary layers was reviewed, first starting from its classical roots and then extending the concepts to the sides, bottoms, and tops of the oceans. During week four, a mini-symposium on “Ocean Bottom and Surface Boundary Layers” gathered a number of oceanographers and meteorologists together to report recent advances. And, finally, Kerry Emanuel of MIT delivered the Sears Public Lecture to a packed hall in Clark 507. The title was “Divine Wind: The History and Sciences of Hurricanes.”
    Beschreibung: Funding was provided by the National Science Foundation under grant OCE-0325296 and by the Office of Naval Research, Processes and Prediction Division, Physical Oceanography Program under grant N00014-07-10776
    Schlagwort(e): Boundary layer ; Ocean circulation
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    Materialart: Technical Report
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  • 85
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    1989 summer study program in Geophysical Fluid Dynamics : general circulation of the oceans (2009)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: The success of this summer's Geophysical Fluid Dynamics Program owes much to Myrl Hendershott's excellent and engaging survey of the Oceans General Circulation, including recent developments In the Theory of Recirculation Gyres and Thermocline Ventilation.
    Beschreibung: Funding was provided by the National Science Foundation through Grant Number OCE-89-01012
    Schlagwort(e): Ocean circulation
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  • 86
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    The influence of convection on large-scale circulations : 1988 Summer Study Program in Geophysical Fluid Dynamics (2009)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: The topic for the 30th Geophysical Fluid Dynamics Summer Program was "The Influence of Convection on Large- Scale Motions." The principal lecturer, Kerry Emanual, presented the essential elements of dry convection, the thermodynamics of moist air, and moist convection (both precipitating and not). Building upon this excellent summary of the fundamentals of atmospheric convection, he then discussed its role in the dynamics of squall lines, tropical cyclones, and the 40-day tropical wave. Moist convection has not been discussed in recent GFD seminars, and Kerry's lectures provided a superb introduction to the topic for both Fellows and Staff. Other meteorologists discussed recent theoretical and observational research on atmospheric convecting systems. Convectively-driven flows in the ocean were described by Peter Killworth; Ed Spiegel and Christian Elphick reviewed the theory of nonlinear convection. These views of convection in other systems lent valuable perspectives on the atmospheric problem.
    Beschreibung: Funding was provided by the Office of Naval Research under contract Number N00014-82-G-0079, and the National Science Foundation through grant Number DMS-85-04166.
    Schlagwort(e): Ocean circulation ; Mathematical models
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  • 87
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    Notes on the 1968 Summer Study Program in Geophysical Fluid Dynamics at the Woods Hole Oceanographic Institution (2009)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: Originally issued as Reference No. 68-72, series later renamed WHOI-.
    Beschreibung: The general circulation of the oceans was the topic of concentration for the 1968 WHOI Summer Program in Geophysical Fluid Dynamics
    Beschreibung: National Science Foundation
    Schlagwort(e): Ocean circulation ; Geophysics ; Fluid models
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  • 88
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    Notes on the 1969 Summer Study Program in Geophysical Fluid Dynamics at the Woods Hole Oceanographic Institution (2009)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: Originally issued as Reference No. 69-41, series later renamed WHOI-.
    Beschreibung: The principal theme of this eleventh Summer Program has been Astrophysical Fluid Dynamics. As in the past, we have explored the region of overlap in technique and theory of our summer theme and other aspects of Fluid Dynamics. An interesting example of this overlap is the application of the physics of salt-finger instability, a significant oceanographic process, to instabilities due to differential rotation in the sun, a critical problem in stellar evolution.
    Beschreibung: National Science Foundation
    Schlagwort(e): Geophysics ; Ocean circulation
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  • 89
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    Diapycnal mixing in the Antarctic Circumpolar Current (2011)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: 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): 241-246, doi:10.1175/2010JPO4557.1.
    Beschreibung: The vertical dispersion of a tracer released on a density surface near 1500-m depth in the Antarctic Circumpolar Current west of Drake Passage indicates that the diapycnal diffusivity, averaged over 1 yr and over tens of thousands of square kilometers, is (1.3 ± 0.2) × 10−5 m2 s−1. Diapycnal diffusivity estimated from turbulent kinetic energy dissipation measurements about the area occupied by the tracer in austral summer 2010 was somewhat less, but still within a factor of 2, at (0.75 ± 0.07) × 10−5 m2 s−1. Turbulent diapycnal mixing of this intensity is characteristic of the midlatitude ocean interior, where the energy for mixing is believed to derive from internal wave breaking. Indeed, despite the frequent and intense atmospheric forcing experienced by the Southern Ocean, the amplitude of finescale velocity shear sampled about the tracer was similar to background amplitudes in the midlatitude ocean, with levels elevated to only 20%–50% above the Garrett–Munk reference spectrum. These results add to a long line of evidence that diapycnal mixing in the interior middepth ocean is weak and is likely too small to dictate the middepth meridional overturning circulation of the ocean.
    Beschreibung: This material is based upon work supported by the National Science Foundation Grants OCE-0622825,OCE-0622670, OCE-0622630, and OCE-0623177.
    Schlagwort(e): Diapycnal mixing ; Currents ; Antarctica ; Ocean circulation ; Meridional overturning circulation
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  • 90
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    2010 program of study : swirling and swimming in turbulence (2012)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: Swirling and Swimming in Turbulence was the theme at the 2010 GFD Program. Professors Glenn Flierl (M.I.T.), Antonello Provenzale (ISAC-CNR, Turin) and Jean-Luc Thiffeault (University of Wisconsin) were the principal lecturers. Together they navigated an elegant path through topics ranging from mixing protocols and efficiencies to ecological strategies, schooling and genetic development. The first ten chapters of this volume document these lectures, each prepared by pairs of this summer’s GFD fellows. Following on are the written reports of the fellows’ own research projects.
    Beschreibung: Funding was provided by the Office of Naval Research under Contract No. N000-14-09-10844 and the National Science Foundation through Grant No. OCE 0824636
    Schlagwort(e): Ocean waves ; Ocean circulation
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  • 91
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    The freshwater system west of the Antarctic Peninsula : spatial and temporal changes (2013)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: 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): 1669–1684, doi:10.1175/JCLI-D-12-00246.1.
    Beschreibung: Climate change west of the Antarctic Peninsula is the most rapid of anywhere in the Southern Hemisphere, with associated changes in the rates and distributions of freshwater inputs to the ocean. Here, results from the first comprehensive survey of oxygen isotopes in seawater in this region are used to quantify spatial patterns of meteoric water (glacial discharge and precipitation) separately from sea ice melt. High levels of meteoric water are found close to the coast, due to orographic effects on precipitation and strong glacial discharge. Concentrations decrease offshore, driving significant southward geostrophic flows (up to ~30 cm s−1). These produce high meteoric water concentrations at the southern end of the sampling grid, where collapse of the Wilkins Ice Shelf may also have contributed. Sea ice melt concentrations are lower than meteoric water and patchier because of the mobile nature of the sea ice itself. Nonetheless, net sea ice production in the northern part of the sampling grid is inferred; combined with net sea ice melt in the south, this indicates an overall southward ice motion. The survey is contextualized temporally using a decade-long series of isotope data from a coastal Antarctic Peninsula site. This shows a temporal decline in meteoric water in the upper ocean, contrary to expectations based on increasing precipitation and accelerating deglaciation. This is driven by the increasing occurrence of deeper winter mixed layers and has potential implications for concentrations of trace metals supplied to the euphotic zone by glacial discharge. As the regional freshwater system evolves, the continuing isotope monitoring described here will elucidate the ongoing impacts on climate and the ecosystem.
    Beschreibung: The Palmer LTER participants acknowledge Award 0823101 from the Organisms and Ecosystems program in NSF OPP
    Beschreibung: 2013-09-01
    Schlagwort(e): Southern Ocean ; Ocean circulation ; Freshwater ; Precipitation ; Snowmelt/icemelt ; Isotopic analysis
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  • 92
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    Sensitivity of the ocean state to the vertical distribution of internal-tide-driven mixing (2013)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: 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): 602–615, doi:10.1175/JPO-D-12-055.1.
    Beschreibung: The ocean interior stratification and meridional overturning circulation are largely sustained by diapycnal mixing. The breaking of internal tides is a major source of diapycnal mixing. Many recent climate models parameterize internal-tide breaking using the scheme of St. Laurent et al. While this parameterization dynamically accounts for internal-tide generation, the vertical distribution of the resultant mixing is ad hoc, prescribing energy dissipation to decay exponentially above the ocean bottom with a fixed-length scale. Recently, Polzin formulated a dynamically based parameterization, in which the vertical profile of dissipation decays algebraically with a varying decay scale, accounting for variable stratification using Wentzel–Kramers–Brillouin (WKB) stretching. This study compares two simulations using the St. Laurent and Polzin formulations in the Climate Model, version 2G (CM2G), ocean–ice–atmosphere coupled model, with the same formulation for internal-tide energy input. Focusing mainly on the Pacific Ocean, where the deep low-frequency variability is relatively small, the authors show that the ocean state shows modest but robust and significant sensitivity to the vertical profile of internal-tide-driven mixing. Therefore, not only the energy input to the internal tides matters, but also where in the vertical it is dissipated.
    Beschreibung: This work is a component of the Internal- Wave Driven Mixing Climate Process Team funded by the National Science Foundation Grant OCE-0968721 and the National Oceanic and Atmospheric Administration, U.S. Department of Commerce, Award NA08OAR4320752.
    Beschreibung: 2013-09-01
    Schlagwort(e): Diapycnal mixing ; Internal waves ; Subgrid-scale processes ; Ocean models ; Parameterization
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  • 93
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    2011 program of study : shear turbulence : onset and structure (2013)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: The theme for the Program in Geophysical Fluid Dynamics for the summer of 2011 was Shear Turbulence: onset and structure. Ten days of principal lectures by FabianWale e and Rich Kerswell began the summer, and a large number of seminars on this and a variety of other topics then continued through the eighth week. These lectures are presented in these Proceedings and form (we believe) the most complete, connected account of this subject) Eleven fellows from around the globe helped to record the principal lectures, and each carried out a project of his/her own, presented in seminar during the tenth and nal week. All these lectures and projects are also presented in this Proceedings volume. The further seminars presented throughout the summer by visitors and (in some cases) by GFD faculty are also listed here. The popular Sears Lecture was given by L. Mahadevan. The title was On growth and form: geometry, physics and biology. It was indeed popular, drawing a large and enthusiastic audience.
    Beschreibung: Funding was provided by the National Science Foundation under Grant No. OCE-0824636 and the Office of Naval Research under Contract No. N00014-09-10844
    Schlagwort(e): Ocean waves ; Ocean circulation ; Fluid dynamics
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  • 94
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    Warm core rings : an interdisciplinary study of warm core ring physics, chemistry, and biology; R/V Endeavor, R/V Knorr, R/V Oceanus June 1982 cruise reports (2014)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Schlagwort(e): Endeavor (Ship: 1976-) Cruise EN86 ; Knorr (Ship : 1970-) Cruise KN95 ; Oceanus (Ship : 1975-) Cruise OC121 ; Albatross IV (Ship) Cruise ; Water masses ; Ocean circulation ; Marine biology ; Chemical oceanography ; Warm Core Rings
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    Materialart: Working Paper
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  • 95
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    Warm core rings workshop report : 18-22 Jan. 1982, Wellington, New Zealand (2014)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: A workshop on the physics, chemistry and biology of warm core rings was held at the New Zealand Oceanographic Institute in Wellington during 18-22 January 1982, under the auspices of the U.S./Australia and U.S./New Zealand Cooperative Science Programs. The purpose of the workshop was to elicit joint discussions and exchange of ideas between groups of scientists actively working on warm core rings or eddies. The workshop consisted of 34 scientific papers summarizing accomplishments resulting from work in warm core rings; working group discussions on particular disciplinary and multi-disciplinary problems associated with ring structure and dynamics; and a final session summarizing the current state of knowledge about rings, and indicating directions for future research.
    Beschreibung: U.S.-Australia Cooperative Science Program; U.S.-New Zealand Cooperative Science Program; DSIR (New Zealand); CSIRO (Australia)
    Schlagwort(e): Ocean currents ; Ocean circulation ; Warm Core Rings
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    Materialart: Working Paper
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    The surface-forced overturning of the North Atlantic : estimates from modern era atmospheric reanalysis datasets (2014)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 27 (2014): 3596–3618, doi:10.1175/JCLI-D-13-00070.1.
    Beschreibung: Estimates of the recent mean and time varying water mass transformation rates associated with North Atlantic surface-forced overturning are presented. The estimates are derived from heat and freshwater surface fluxes and sea surface temperature fields from six atmospheric reanalyses—the Japanese 25-yr Reanalysis (JRA), the NCEP–NCAR reanalysis (NCEP1), the NCEP–U.S. Department of Energy (DOE) reanalysis (NCEP2), the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-I), the Climate Forecast System Reanalysis (CFSR), and the Modern-Era Reanalysis for Research and Applications (MERRA)—together with sea surface salinity fields from two globally gridded datasets (World Ocean Atlas and Met Office EN3 datasets). The resulting 12 estimates of the 1979–2007 mean surface-forced streamfunction all depict a subpolar cell, with maxima north of 45°N, near σ = 27.5 kg m−3, and a subtropical cell between 20° and 40°N, near σ = 26.1 kg m−3. The mean magnitude of the subpolar cell varies between 12 and 18 Sv (1 Sv ≡ 106 m3 s−1), consistent with estimates of the overturning circulation from subsurface observations. Analysis of the thermal and haline components of the surface density fluxes indicates that large differences in the inferred low-latitude circulation are largely a result of the biases in reanalysis net heat flux fields, which range in the global mean from −13 to 19 W m−2. The different estimates of temporal variability in the subpolar cell are well correlated with each other. This suggests that the uncertainty associated with the choice of reanalysis product does not critically limit the ability of the method to infer the variability in the subpolar overturning. In contrast, the different estimates of subtropical variability are poorly correlated with each other, and only a subset of them captures a significant fraction of the variability in independently estimated North Atlantic Subtropical Mode Water volume.
    Beschreibung: JPG is funded by UK Natural Environment Research Council New Investigator Grant NE/I001654/1. Y-OK was supported by the U.S. National Science Foundation under Grant OCE-0424492. RJB is supported by a fellowship from the UK National Centre for Earth Observation.
    Beschreibung: 2014-11-15
    Schlagwort(e): Atmosphere-ocean interaction ; Meridional overturning circulation ; Ocean circulation
    Repository-Name: Woods Hole Open Access Server
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    Properties and origins of the anisotropic eddy-induced transport in the North Atlantic (2015)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 778–791, doi:10.1175/JPO-D-14-0164.1.
    Beschreibung: This study examines anisotropic transport properties of the eddying North Atlantic flow, using an idealized model of the double-gyre oceanic circulation and altimetry-derived velocities. The material transport by the time-dependent flow (quantified by the eddy diffusivity tensor) varies geographically and is anisotropic, that is, it has a well-defined direction of the maximum transport. One component of the time-dependent flow, zonally elongated large-scale transients, is particularly important for the anisotropy, as it corresponds to primarily zonal material transport and long correlation time scales. The importance of these large-scale zonal transients in the material distribution is further confirmed with simulations of idealized color dye tracers, which has implications for parameterizations of the eddy transport in non-eddy-resolving models.
    Beschreibung: IK would like to acknowledge support through the NSF Grant OCE-1154923. IR was supported by the NSF OCE-1154641 and NASA Grant NNX14AH29G.
    Beschreibung: 2015-09-01
    Schlagwort(e): Circulation/ Dynamics ; Eddies ; Lagrangian circulation/transport ; Mesoscale processes ; Ocean circulation ; Models and modeling ; Tracers
    Repository-Name: Woods Hole Open Access Server
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    A bibliography of physical, chemical, and biological studies of rings in the world's oceans (2014)
    Woods Hole Oceanographic Institution
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    Publikationsdatum: 2022-05-26
    Beschreibung: This bibliography marks the end of several years of sporadic attempts to put together a set of references on rings. The scope of the effort encompasses the chemistry, biology, and physics of the long-lived, coherent features which are commonly referred to as rings after Fuglister (1972). There is a vast literature on the mesoscale eddy field in different parts of the world. The present set of references includes a subset of this body of work. The basic criterion used in the compilation of this bibliography is fairly narrow compared to the range of eddies found in the world's oceans. The emphasis here is on the highly nonlinear features formed due to the instability processes in boundary currents and in the planetary scale jet which surrounds the Antarctic. The nomenclature "ring", refers to the strong encircling current which forms a kinematic trap in which the core of the ring is embedded.
    Schlagwort(e): Water masses ; Ocean circulation ; Marine biology ; Chemical oceanography
    Repository-Name: Woods Hole Open Access Server
    Materialart: Working Paper
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    On the observability of oceanic gyres (2014)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 2498–2523, doi:10.1175/JPO-D-13-0183.1.
    Beschreibung: This study examines the observability of a stratified ocean in a square flat basin on a midlatitude beta plane. Here, “observability” means the ability to establish, in a finite interval of time, the time-dependent ocean state given density observations over the same interval and with no regard for errors. The dynamics is linearized and hydrostatic, so that the motion can be decomposed into normal modes and the observability analysis is simplified. An observability Gramian (a symmetric matrix) is determined for the flows in an inviscid interior, in frictional boundary layers, and in a closed basin. Its properties are used to establish the condition for complete observability and to identify optimal data locations for each of these flows. It is found that complete observability of an oceanic interior in time-dependent Sverdrup balance requires that the observations originate from the westernmost location at each considered latitude. The degree of observability increases westward due to westward propagation of long baroclinic Rossby waves: data collected in the west are more informative than data collected in the east. Likewise, the best locations for observing variability in the western (eastern) boundary layer are near (far from) the boundary. The observability of a closed basin is influenced by the westward propagation and the boundaries. Optimal data locations that are identified for different resolutions (0.01 to 1 yr) and lengths of data records (0.2 to 20 yr) show a variable influence of the planetary vorticity gradient. Data collected near the meridional boundaries appear always less informative, from the viewpoint of basin observability, than data collected away from these boundaries.
    Beschreibung: This work was supported by the U.S. National Science Foundation.
    Beschreibung: 2015-03-01
    Schlagwort(e): Circulation/ Dynamics ; Ocean circulation ; Rossby waves ; Mathematical and statistical techniques ; Inverse methods ; Variability ; Oceanic variability
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    Observed deep cyclonic eddies around Southern Greenland (2022)
    American Meteorological Society
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    Publikationsdatum: 2022-06-06
    Beschreibung: Author Posting. © American Meteorological Society, 2021. 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 51(10), (2021): 3235–3252, https://doi.org/10.1175/JPO-D-20-0288.1.
    Beschreibung: Recent mooring measurements from the Overturning in the Subpolar North Atlantic Program have revealed abundant cyclonic eddies at both sides of Cape Farewell, the southern tip of Greenland. In this study, we present further observational evidence, from both Eulerian and Lagrangian perspectives, of deep cyclonic eddies with intense rotation (ζ/f 〉 1) around southern Greenland and into the Labrador Sea. Most of the observed cyclones exhibit strongest rotation below the surface at 700–1000 dbar, where maximum azimuthal velocities are ~30 cm s−1 at radii of ~10 km, with rotational periods of 2–3 days. The cyclonic rotation can extend to the deep overflow water layer (below 1800 dbar), albeit with weaker azimuthal velocities (~10 cm s−1) and longer rotational periods of about one week. Within the middepth rotation cores, the cyclones are in near solid-body rotation and have the potential to trap and transport water. The first high-resolution hydrographic transect across such a cyclone indicates that it is characterized by a local (both vertically and horizontally) potential vorticity maximum in its middepth core and cold, fresh anomalies in the deep overflow water layer, suggesting its source as the Denmark Strait outflow. Additionally, the propagation and evolution of the cyclonic eddies are illustrated with deep Lagrangian floats, including their detachments from the boundary currents to the basin interior. Taken together, the combined Eulerian and Lagrangian observations have provided new insights on the boundary current variability and boundary–interior exchange over a geographically large scale near southern Greenland, calling for further investigations on the (sub)mesoscale dynamics in the region.
    Beschreibung: OOI mooring data are based upon work supported by the National Science Foundation under Cooperative Agreement 1743430. S. Zou, A. Bower, and H. Furey gratefully acknowledge the support from the Physical Oceanography Program of the U.S. National Science Foundation Grant OCE-1756361. R.S. Pickart acknowledges support from National Science Foundation Grants OCE-1259618 and OCE-1756361. N. P. Holliday and L. Houpert were supported by NERC programs U.K. OSNAP (NE/K010875) and U.K. OSNAP-Decade (NE/T00858X/1).
    Schlagwort(e): North Atlantic Ocean ; Cyclogenesis/cyclolysis ; Lagrangian circulation/transport ; Mesoscale processes ; Ocean circulation
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