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  • Artikel  (18)
  • In situ observations  (10)
  • Coastal flows  (9)
  • American Meteorological Society  (18)
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  • American Meteorological Society  (18)
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  • 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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    Response to a steady poleward outflow. Part I : the linear, quasigeostrophic problem (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): 1541-1550, doi:10.1175/2008JPO3999.1.
    Beschreibung: The response of a zonal channel to a uniform, switched-on but subsequently steady poleward outflow is presented. An eastward coastal current with a Kelvin wave’s cross-shore structure is found to be generated instantly upon initiation of the outflow. The current is essentially in geostrophic balance everywhere except for the vicinity of the outflow channel mouth, where the streamlines must cross planetary vorticity contours to feed the current. The adjustment of this region generates a plume that propagates westward at Rossby wave speeds. The cross-shore structure of the plume varies with longitude, and at any given longitude it evolves with time. The authors show that the plume evolution can be understood both conceptually and quantitatively as the westward propagation of the Kelvin current’s meridional spectrum, with each spectral element propagating at its own Rossby wave group velocity.
    Beschreibung: This work was completed at Woods Hole Oceanographic Institution while T.S. Durland was supported by the Ocean and Climate Change Institute. M.A. Spall was supported by NSF Grant OCE-0423975, and J. Pedlosky by NSF Grant OCE-0451086. T.S. Durland acknowledges additional report preparation support from NASA Grant NNG05GN98G.
    Schlagwort(e): Coastal flows ; Estuaries ; Currents ; Vorticity ; Plumes
    Repository-Name: Woods Hole Open Access Server
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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
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  • 4
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    Winter mixed layer development in the central Irminger Sea : the effect of strong, intermittent wind events (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): 541-565, doi:10.1175/2007JPO3678.1.
    Beschreibung: The impact of the Greenland tip jet on the wintertime mixed layer of the southwest Irminger Sea is investigated using in situ moored profiler data and a variety of atmospheric datasets. The mixed layer was observed to reach 400 m in the spring of 2003 and 300 m in the spring of 2004. Both of these winters were mild and characterized by a low North Atlantic Oscillation (NAO) index. A typical tip jet event is associated with a low pressure system that is advected by upper-level steering currents into the region east of Cape Farewell and interacts with the high topography of southern Greenland. Heat flux time series for the mooring site were constructed that include the enhancing influence of the tip jet events. This was used to force a one-dimensional mixed layer model, which was able to reproduce the observed envelope of mixed layer deepening in both winters. The deeper mixed layer of the first winter was largely due to a higher number of robust tip jet events, which in turn was caused by the steering currents focusing more storms adjacent to southern Greenland. Application of the mixed layer model to the winter of 1994–95, a period characterized by a high-NAO index, resulted in convection exceeding 1700 m. This prediction is consistent with hydrographic data collected in summer 1995, supporting the notion that deep convection can occur in the Irminger Sea during strong winters.
    Beschreibung: KV and RP were supported by National Science Foundation Grant OCE-0450658. GWKM was supported by the Canadian Foundation for Climate and Atmospheric Sciences. MHR was supported by the Nordic Council of Ministers (West-Nordic Ocean Climate).
    Schlagwort(e): Mixed layer ; Europe ; Wind effects ; In situ observations ; North Atlantic Oscillation
    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
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  • 6
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    Improving HF radar estimates of surface currents using signal quality metrics, with application to the MVCO high-resolution radar system (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 Atmospheric and Oceanic Technology 29 (2012): 1377–1390, doi:10.1175/JTECH-D-11-00160.1.
    Beschreibung: Estimates of surface currents over the continental shelf are now regularly made using high-frequency radar (HFR) systems along much of the U.S. coastline. The recently deployed HFR system at the Martha’s Vineyard Coastal Observatory (MVCO) is a unique addition to these systems, focusing on high spatial resolution over a relatively small coastal ocean domain with high accuracy. However, initial results from the system showed sizable errors and biased estimates of M2 tidal currents, prompting an examination of new methods to improve the quality of radar-based velocity data. The analysis described here utilizes the radial metric output of CODAR Ocean Systems’ version 7 release of the SeaSonde Radial Site Software Suite to examine both the characteristics of the received signal and the output of the direction-finding algorithm to provide data quality controls on the estimated radial currents that are independent of the estimated velocity. Additionally, the effect of weighting spatial averages of radials falling within the same range and azimuthal bin is examined to account for differences in signal quality. Applied to two month-long datasets from the MVCO high-resolution system, these new methods are found to improve the rms difference comparisons with in situ current measurements by up to 2 cm s−1, as well as reduce or eliminate observed biases of tidal ellipses estimated using standard methods.
    Beschreibung: 2013-03-01
    Schlagwort(e): Coastal flows ; Currents ; Data processing ; Data quality control ; In situ atmospheric observations ; Remote sensing
    Repository-Name: Woods Hole Open Access Server
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  • 7
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    Laboratory experiments on the interaction of a buoyant coastal current with a canyon : application to the East Greenland Current (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): 1258-1271, doi:10.1175/2008JPO4028.1.
    Beschreibung: This paper presents a set of laboratory experiments focused on how a buoyant coastal current flowing over a sloping bottom interacts with a canyon and what controls the separation, if any, of the current from the upstream canyon bend. The results show that the separation of a buoyant coastal current depends on the current width W relative to the radius of curvature of the bathymetry ρc. The flow moved across the mouth of the canyon (i.e., separated) for W/ρc 〉 1, in agreement with previous results. The present study extends previous work by examining both slope-controlled and surface-trapped currents, and using a geometry specific to investigating buoyant current–canyon interaction. The authors find that, although bottom friction is important in setting the position of the buoyant front, the separation process driven by the inertia of the flow could overcome even the strongest bathymetric influence. Application of the laboratory results to the East Greenland Current (EGC), an Arctic-origin buoyant current that is observed to flow in two branches south of Denmark Strait, suggests that the path of the EGC is influenced by the large canyons cutting across the shelf, as the range of W/ρc in the ocean spans those observed in the laboratory. What causes the formation of a two-branched EGC structure downstream of the Kangerdlugssuaq Canyon (68°N, 32°W) is still unclear, but potential mechanisms are discussed.
    Beschreibung: This work was partially funded by NSF Grant OCE-0450658. DS also received support from the Academic Programs Office of the Woods Hole Oceanographic Institution, while CC had partial support from NSF OCE-0350891.
    Schlagwort(e): Coastal flows ; Buoyancy ; Currents ; Experimental design ; Topographic effects
    Repository-Name: Woods Hole Open Access Server
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  • 8
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    Observations and a model of undertow over the inner 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): 2341-2357, doi:10.1175/2008JPO3986.1.
    Beschreibung: Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth. During weak winds, wave-driven cross-shelf velocity profiles over the inner shelf have maximum offshore flow (1–6 cm s−1) and vertical shear near the surface and weak flow and shear in the lower half of the water column. The observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the surf zone. Instead, the vertical structure is similar to the Stokes drift velocity profile but with the opposite direction. This vertical structure is consistent with a dynamical balance between the Coriolis force associated with the offshore flow and an along-shelf “Hasselmann wave stress” due to the influence of the earth’s rotation on surface gravity waves. The close agreement between the observed and modeled profiles provides compelling evidence for the importance of the Hasselmann wave stress in forcing oceanic flows. Summer profiles are more vertically sheared than either winter profiles or model profiles, for reasons that remain unclear.
    Beschreibung: This research was funded by the Ocean Sciences Division of the National Science Foundation under Grants OCE-0241292 and OCE-0548961.
    Schlagwort(e): Continental shelf ; Transport ; Shear structure/flows ; Coastal flows ; Gravity waves
    Repository-Name: Woods Hole Open Access Server
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  • 9
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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
    Repository-Name: Woods Hole Open Access Server
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  • 10
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    The coastal bottom boundary layer : a note on the model of Chapman and Lentz (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): 2776-2784, doi:10.1175/2007JPO3710.1.
    Beschreibung: The bottom boundary layer of a stratified flow on a coastal continental shelf is examined using the model of Chapman and Lentz. The flow is driven by a surface stress, uniform in the alongshore coordinate, in a downwelling-favorable direction. The stress diminishes in the offshore direction and produces an Ekman pumping, as well as an onshore Ekman flux. The model yields an interior flow, sandwiched between an upper Ekman layer and a bottom boundary layer. The interior has a horizontal density gradient produced by a balance between horizontal diffusion of density and vertical advection of a background vertical density gradient. The interior flow is vertically sheared and in thermal wind balance. Whereas the original model of Chapman and Lentz considered an alongshore flow that is freely evolving, the present note focuses on the equilibrium structure of a flow driven by stress and discusses the vertical and lateral structure of the flow and, in particular, the boundary layer thickness. The vertical diffusivity of density in the bottom boundary layer is considered so strong, locally, as to render the bottom boundary layer’s density a function of only offshore position. Boundary layer budgets of mass, momentum, and buoyancy determine the barotropic component of the interior flow as well as the boundary layer thickness, which is a function of the offshore coordinate. The alongshore flow has enhanced vertical shear in the boundary layer that reduces the alongshore flow in the boundary layer; however, the velocity at the bottom is generally not zero but produces a stress that locally balances the applied surface stress. The offshore transport in the bottom boundary layer therefore balances the onshore surface Ekman flux. The model predicts the thickness of the bottom boundary layer, which is a complicated function of several parameters, including the strength of the forcing stress, the vertical and horizontal diffusion coefficients in the interior, and the horizontal diffusion in the boundary layer. The model yields a boundary layer over only a finite portion of the bottom slope if the interior diffusion coefficients are too large; otherwise, the layer extends over the full lateral extent of the domain.
    Beschreibung: This research was supported in part by NSF Grant OCE-851086.00.
    Schlagwort(e): Boundary layer ; Continental shelf ; Coastal flows ; Ekman pumping ; Forcing
    Repository-Name: Woods Hole Open Access Server
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  • 11
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    Three-dimensional mapping of fluorescent dye using a scanning, depth-resolving airborne lidar (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 Atmospheric and Oceanic Technology 24 (2007): 1050-1065, doi:10.1175/JTECH2027.1.
    Beschreibung: Results are presented from a pilot study using a fluorescent dye tracer imaged by airborne lidar in the ocean surface layer on spatial scales of meters to kilometers and temporal scales of minutes to hours. The lidar used here employs a scanning, frequency-doubled Nd:YAG laser to emit an infrared (1064 nm) and green (532 nm) pulse 6 ns in duration at a rate of 1 kHz. The received signal is split to infrared, green, and fluorescent (nominally 580–600 nm) channels, the latter two of which are used to compute absolute dye concentration as a function of depth and horizontal position. Comparison of dye concentrations inferred from the lidar with in situ fluorometry measurements made by ship shows good agreement both qualitatively and quantitatively for absolute dye concentrations ranging from 1 to 〉10 ppb. Uncertainties associated with horizontal variations in the natural seawater attenuation are approximately 1 ppb. The results demonstrate the ability of airborne lidar to capture high-resolution three-dimensional “snapshots” of the distribution of the tracer as it evolves over very short time and space scales. Such measurements offer a powerful observational tool for studies of transport and mixing on these scales.
    Beschreibung: Support was provided by the Cecil H. and Ida M. Green Technology Innovation Fund under Grant 27001545, the Office of Naval Research Grant N00014-01-1-0984, and the Woods Hole Oceanographic Institution Coastal Ocean Institute.
    Schlagwort(e): Lidars ; In situ observations ; Aircraft observations
    Repository-Name: Woods Hole Open Access Server
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  • 12
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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
    Repository-Name: Woods Hole Open Access Server
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  • 13
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    Acoustic detection of oceanic double-diffusive convection : a feasibility study (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 Atmospheric and Oceanic Technology 27 (2010): 580-593, doi:10.1175/2009JTECHO696.1.
    Beschreibung: The feasibility of using high-frequency acoustic scattering techniques to map the extent and evolution of the diffusive regime of double-diffusive convection in the ocean is explored. A scattering model developed to describe acoustic scattering from double-diffusive interfaces in the laboratory, which accounted for much of the measured scattering in the frequency range from 200 to 600 kHz, is used in conjunction with published in situ observations of diffusive-convection interfaces to make predictions of acoustic scattering from oceanic double-diffusive interfaces. Detectable levels of acoustic scattering are predicted for a range of different locations in the world’s oceans. To corroborate these results, thin acoustic layers detected near the western Antarctic Peninsula using a multifrequency acoustic backscattering system are shown to be consistent with scattering from diffusive-convection interfaces.
    Beschreibung: TR is grateful to the Natural Sciences and Engineering Research Council of Canada Discovery Grant and University Faculty Award Programs, which support her work at Dalhousie University.
    Schlagwort(e): Acoustic measurements/effects ; Convection ; Antarctica ; In situ observations
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  • 14
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    Seasonal kinetic energy variability of near-inertial motions (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): 1035-1049, doi:10.1175/2008JPO3920.1.
    Beschreibung: Seasonal variability of near-inertial horizontal kinetic energy is examined using observations from a series of McLane Moored Profiler moorings located at 39°N, 69°W in the western North Atlantic Ocean in combination with a one-dimensional, depth-integrated kinetic energy model. The time-mean kinetic energy and shear vertical wavenumber spectra of the high-frequency motions at the mooring site are in reasonable agreement with the Garrett–Munk internal wave description. Time series of depth-dependent and depth-integrated near-inertial kinetic energy are calculated from available mooring data after filtering to isolate near-inertial-frequency motions. These data document a pronounced seasonal cycle featuring a wintertime maximum in the depth-integrated near-inertial kinetic energy deriving chiefly from the variability in the upper 500 m of the water column. The seasonal signal in the near-inertial kinetic energy is most prominent for motions with vertical wavelengths greater than 100 m but observable wintertime enhancement is seen down to wavelengths of the order of 10 m. Rotary vertical wavenumber spectra exhibit a dominance of clockwise-with-depth energy, indicative of downward energy propagation and implying a surface energy source. A simple depth-integrated near-inertial kinetic energy model consisting of a wind forcing term and a dissipation term captures the order of magnitude of the observed near-inertial kinetic energy as well as its seasonal cycle.
    Beschreibung: Funding to initiate the McLane Moored Profiler observations at Line W were provided by grants from the G. Unger Vetlesen Foundation and the Comer Charitable Fund to the Woods Hole Oceanographic Institution’s Ocean and Climate Change Institute. Ongoing moored observations at Line W are supported by the National Science Foundation (NSF Grant OCE-0241354).
    Schlagwort(e): Kinetic energy ; Internal waves ; Intraseasonal variability ; North Atlantic Ocean ; In situ observations
    Repository-Name: Woods Hole Open Access Server
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  • 15
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    Long-term performance of Aanderaa optodes and Sea-Bird SBE-43 dissolved-oxygen sensors bottom mounted at 32 m in Massachusetts Bay (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 Atmospheric and Oceanic Technology 24 (2007): 1924-1935, doi:10.1175/JTECH2078.1.
    Beschreibung: A field evaluation of two new dissolved-oxygen sensing technologies, the Aanderaa Instruments AS optode model 3830 and the Sea-Bird Electronics, Inc., model SBE43, was carried out at about 32-m water depth in western Massachusetts Bay. The optode is an optical sensor that measures fluorescence quenching by oxygen molecules, while the SBE43 is a Clark polarographic membrane sensor. Optodes were continuously deployed on bottom tripod frames by exchanging sensors every 4 months over a 19-month period. A Sea-Bird SBE43 was added during one 4-month deployment. These moored observations compared well with oxygen measurements from profiles collected during monthly shipboard surveys conducted by the Massachusetts Water Resources Authority. The mean correlation coefficient between the moored measurements and shipboard survey data was 〉0.9, the mean difference was 0.06 mL L−1, and the standard deviation of the difference was 0.15 mL L−1. The correlation coefficient between the optode and the SBE43 was 〉0.9 and the mean difference was 0.07 mL L−1. Optode measurements degraded when fouling was severe enough to block oxygen molecules from entering the sensing foil over a significant portion of the sensing window. Drift observed in two optodes beginning at about 225 and 390 days of deployment is attributed to degradation of the sensing foil. Flushing is necessary to equilibrate the Sea-Bird sensor. Power consumption by the SBE43 and required pump was 19.2 mWh per sample, and the optode consumed 0.9 mWh per sample, both within expected values based on manufacturers’ specifications.
    Beschreibung: This work was funded by the MWRA and USGS.
    Schlagwort(e): Instrumentation ; Sensors ; Ocean dynamics ; Ship observations ; In situ observations
    Repository-Name: Woods Hole Open Access Server
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  • 16
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    Estuarine exchange flow quantified with isohaline coordinates : contrasting long and short estuaries (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): 748–763, doi:10.1175/JPO-D-11-086.1.
    Beschreibung: Isohaline coordinate analysis is used to compare the exchange flow in two contrasting estuaries, the long (with respect to tidal excursion) Hudson River and the short Merrimack River, using validated numerical models. The isohaline analysis averages fluxes in salinity space rather than in physical space, yielding the isohaline exchange flow that incorporates both subtidal and tidal fluxes and precisely satisfies the Knudsen relation. The isohaline analysis can be consistently applied to both subtidally and tidally dominated estuaries. In the Hudson, the isohaline exchange flow is similar to results from the Eulerian analysis, and the conventional estuarine theory can be used to quantify the salt transport based on scaling with the baroclinic pressure gradient. In the Merrimack, the isohaline exchange flow is much larger than the Eulerian quantity, indicating the dominance of tidal salt flux. The exchange flow does not scale with the baroclinic pressure gradient but rather with tidal volume flux. This tidal exchange is driven by tidal pumping due to the jet–sink flow at the mouth constriction, leading to a linear dependence of exchange flow on tidal volume flux. Finally, a tidal conversion parameter Qin/Qprism, measuring the fraction of tidal inflow Qprism that is converted into net exchange Qin, is proposed to characterize the exchange processes among different systems. It is found that the length scale ratio between tidal excursion and salinity intrusion provides a characteristic to distinguish estuarine regimes.
    Beschreibung: SNC is supported by a WHOI postdoctoral scholarship, a NSF Grant OCE-0926427, and a Taiwan National Science Council Grant NSC 100- 2199-M-002-028.WRGis supported byNSFGrantOCE- 0926427. JAL is supported by NSF Grant OCE-0452054.
    Beschreibung: 2012-11-01
    Schlagwort(e): Coastal flows
    Repository-Name: Woods Hole Open Access Server
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  • 17
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    On the nature and variability of the east Greenland Spill Jet : a case study in Summer 2003 (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 Physical Oceanography 41 (2011): 2307–2327, doi:10.1175/JPO-D-10-05004.1.
    Beschreibung: Results from a high-resolution (~2 km) numerical simulation of the Irminger Basin during summer 2003 are presented. The focus is on the East Greenland Spill Jet, a recently discovered component of the circulation in the basin. The simulation compares well with observations of surface fields, the Denmark Strait overflow (DSO), and the hydrographic structure of typical sections in the basin. The model reveals new aspects of the circulation on scales of O(0.1–10) days and O(1–100) km. The model Spill Jet results from the cascade of dense waters over the East Greenland shelf. Spilling can occur in various locations southwest of the strait, and it is present throughout the simulation but exhibits large variations on periods of O(0.1–10) days. The Spill Jet sometimes cannot be distinguished in the velocity field from surface eddies or from the DSO. The vorticity structure of the jet confirms its unstable nature with peak relative and tilting vorticity terms reaching twice the planetary vorticity term. The average model Spill Jet transport is 4.9 ±1.7 Sv (1 Sv ≡ 106 m3 s−1) equatorward, about 2½ times larger than has been previously reported from a single ship transect in August 2001. Kinematic analysis of the model results suggests two different types of spilling events. In the first case (type I), a local perturbation results in dense waters descending over the shelf break into the Irminger Basin. In the second case (type II), surface cyclones associated with DSO deep domes initiate the spilling process. During summer 2003, more than half of the largest Spill Jet transport values are of type II.
    Beschreibung: The research is supported by the National Science Foundation Grants OCE-0726393 and OCI-0904640 (MGM and TWNH) and OCE-0726640 (RSP).
    Beschreibung: 2012-06-01
    Schlagwort(e): North Atlantic Ocean ; In situ observations ; Regional models
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 18
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    Buoyancy arrest and shelf–ocean exchange (2012)
    American Meteorological Society
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    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): 644–658, doi:10.1175/JPO-D-11-0143.1.
    Beschreibung: When steady flow in a stratified ocean passes between the continental slope and open ocean, its ability to cross isobaths is potentially limited by buoyancy arrest. If the bottom Ekman transport vanishes and there are no interior stresses, then steady linear flow on an f plane must be geostrophic and follow isobaths exactly. The influence of arrest on cross-shelf transport is investigated here to establish 1) whether there are substantial penetration asymmetries between cases with upwelling and downwelling in the bottom boundary layer; 2) over what spatial scales, hence in what parameter regime, buoyancy arrest is important; and 3) the effects of depth-dependent interior flow. The problem is approached using scalings and idealized numerical models. The results show that there is little or no asymmetry introduced by bottom boundary layer behavior. Further, if the stratification is weak or moderate, as measured by a slope Burger number s = αN/f (where α is the bottom slope, N is buoyancy frequency, and f is the Coriolis parameter), buoyancy arrest does not exert a strong constraint on cross-isobath exchange.
    Beschreibung: This research was supported by the National Science Foundation Physical Oceanography program through Grant OCE-0849498.
    Beschreibung: 2012-10-01
    Schlagwort(e): Coastal flows ; Ekman pumping/transport
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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