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  • 1
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    Water column structure and statistics of Denmark Strait Overflow Water cyclones (2014)
    Elsevier
    In:  EPIC3Deep Sea Research Part I: Oceanographic Research Papers, Elsevier, 84, pp. 110-126, ISSN: 0967-0637
    Details
    Publication Date: 2014-04-04
    Description: Data from seven moorings deployed across the East Greenland shelfbreak and slope 280 km downstream of Denmark Strait are used to investigate the characteristics and dynamics of Denmark Strait Overflow Water (DSOW) cyclones. On average, a cyclone passes the mooring array every other day near the 900 m isobath, dominating the variability of the boundary current system. There is considerable variation in both the frequency and location of the cyclones on the slope, but no apparent seasonality. Using the year-long data set from September 2007 to October 2008, we construct a composite DSOW cyclone that reveals the average scales of the features. The composite cyclone consists of a lens of dense overflow water on the bottom, up to 300 m thick, with cyclonic flow above the lens. The azimuthal flow is intensified in the middle and upper part of the water column and has the shape of a Gaussian eddy with a peak depth-mean speed of 0.22 m/s at a radius of 7.8 km. The lens is advected by the mean flow of 0.27 m/s and self propagates at 0.45 m/s, consistent with the topographic Rossby wave speed and the Nof speed. The total translation velocity along the East Greenland slope is 0.72 m/s. The self-propagation speed exceeds the cyclonic swirl speed, indicating that the azimuthal flow cannot kinematically trap fluid in the water column above the lens. This implies that the dense water anomaly and the cyclonic swirl velocity are dynamically linked, in line with previous theory. Satellite sea surface temperature (SST) data are investigated to study the surface expression of the cyclones. Disturbances to the SST field are found to propagate less quickly than the in-situ DSOW cyclones, raising the possibility that the propagation of the SST signatures is not directly associated with the cyclones.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Bottom boundary layer flow and salt injection from the continental shelf to slope (2006)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2006. 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 33 (2006): L13608, doi:10.1029/2006GL026311.
    Description: Austral winter oceanographic measurements from the northwest Australian continental shelf reveal salty water forming evaporatively inshore, moving across the wide shelf near the bottom and into the adjacent open ocean when the shelf edge alongshore flow is equatorward. The salt tongue is absent during more normal conditions, when the poleward Leeuwin Current is present. We hypothesize that the flow reversal enables shelf-wide bottom boundary layer (Ekman) transport and thus creates the shelf-edge convergence that accounts for the observed salt tongue. This flow is absent under sustained normal conditions because of buoyancy arrest in the bottom boundary layer.
    Description: This research was supported by the Processes and Prediction Division (Code 322 PO) of the U.S. Office of Naval Research through grant N00014-02-1-0767.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    What determines the spatial pattern in summer upwelling trends on the U.S. West Coast? (2012)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2012. 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 117 (2012): C08012, doi:10.1029/2012JC008016.
    Description: Analysis of sea surface temperature (SST) from coastal buoys suggests that the summertime over-shelf water temperature off the U.S. West Coast has been declining during the past 30 years at an average rate of −0.19°C decade−1. This cooling trend manifests itself more strongly off south-central California than off Oregon and northern California. The variability and trend in the upwelling north of off San Francisco are positively correlated with those of the equatorward wind, indicating a role of offshore Ekman transport in the north. In contrast, Ekman pumping associated with wind stress curls better explains the stronger and statistically more significant cooling trend in the south. While the coast-wide variability and trend in SST are strongly correlated with those of large-scale modes of climate variability, they in general fail to explain the southward intensification of the trend in SST and wind stress curl. This result suggests that the local wind stress curl, often topographically forced, may have played a role in the upwelling trend pattern.
    Description: H.S. acknowledges the WHOI supports from the Coastal Research Fund in Support of Scientific Staff, the Penzance Endowed Fund in Support of Assistant Scientists, and the Andrew W. Mellon Foundation Endowed Fund for Innovative Research. K.B. and C.E. acknowledge support by the National Science Foundation through grants OCE-1059632 and OCE 1061434.
    Description: 2013-03-09
    Keywords: Coastal upwelling ; Multidecadal trend ; Wind stress curl
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Coastal-trapped waves with finite bottom friction (2007)
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    Publication Date: 2022-05-25
    Description: Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Dynamics of Atmospheres and Oceans 41 (2006): 172-190, doi:10.1016/j.dynatmoce.2006.05.001.
    Description: Coastal-trapped waves with finite-amplitude bottom friction are explored. “Finite-amplitude” in this context means that the bottom stresses are large enough to change the wave modal structure. The importance of bottom friction is measured by the nondimensional number r/(ωh), where r is a bottom resistance coefficient, ω is the wave frequency and h is the water depth. Increasing bottom drag causes free wave modes to adjust by having their amplitude maxima for alongshore current translate offshore to the point that, with relatively large bottom stress, the alongshore current variance is trapped entirely on the slope, even though pressure variations remain substantial right up to the coast. In conjunction with these adjustments, wave frequency, hence propagation speed, varies and the wave damping is usually less than would be expected based on a weak-friction perturbation calculation. Stronger density stratification increases wave damping, all else being the same. A mean alongshore flow can strongly affect modal structure and wave damping, although general trends are difficult to discern. Results suggest that bottom friction may cause an observed tendency for lower frequency alongshore current fluctuations to become relatively more important with distance offshore.
    Description: This work was supported by National Science Foundation grant number OCE02-27679.
    Keywords: Coastal-trapped waves ; Bottom friction
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 5
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    Cross-shelf exchange (2016)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Annual Reviews for personal use, not for redistribution. The definitive version was published in Annual Review of Marine Science 8 (2016): 59-78, doi:10.1146/annurev-marine-010814-015717.
    Description: Cross-shelf exchange dominates the pathways and rates by which nutrients, biota and materials on the continental shelf are delivered and removed. These transports are limited by Earth’s rotation, which inhibits flow from crossing isobaths. Thus, cross-shelf transports are generally weak compared to alongshore flows, and this leads to interesting observational issues. Cross-shelf flows are enabled by turbulent mixing processes, by nonlinear processes (such as momentum advection), and by time-dependence. Thus, there is a wide range of possible effects that can allow these critical transports, and different natural settings are often governed by differing mixes of processes. Examples of representative transport mechanisms are discussed, and possible observational and theoretical paths to future progress are explored.
    Description: Support from the National Science Foundation Physical Oceanography program, through grant OCE-1433953, and the Biological Oceanography program through grant OCE-1258667
    Keywords: Coastal physical oceanography ; Turbulent boundary layers ; Coastal instabilities ; Nutrient supplies ; Wind forcing
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 6
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    Coastal Ocean Processes : a science prospectus (2006)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: CoOP (Coastal Ocean Processes) is an organization meant to study major interdisciplinary scientific problems in the coastal ocean. Its goal is "to obtain a new level of quantitative understanding of the processes that dominate the transformations, transport and fates of biologically, chemically and geologically important matter on the continental margin". Central to obtaining this understanding will be advances in observing and modeling the cross-shelf component of transport. More specific objectives are to understand 1) cross-margin exchanges, 2) air sea exchanges, 3) benthic-pelagic exchanges, 4) terrestrial inputs and 5) biological and chemical transformations within the water column. CoOP research will be carried out primarly through a series of process-oriented field studies, each involving about two years of measurements. Each of these field studies is to be initiated and defined through a community workshop. In addition to the process studies, CoOP will also involve modeling, long time series, exploratory studies, remote sensing, technological innovation, data archiving and communications. A CoOP pilot study has been approved for funding by the National Science Foundation, and funding will begin in 1992. The CoOP science effort is thus already underway.
    Description: Funding was provided by the National Science Foundation under Grant No. OCE-9108993.
    Keywords: Coastal oceanography ; Coastal meteorology ; Continental shelf
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 9125740 bytes
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  • 7
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    Coastal Ocean Processes program : advancing interdisciplinary research and technology development (2009)
    Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Oceanography Society, 2008. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 21, 4 (2008): 18-21.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    A large-amplitude meander of the shelfbreak front during summer south of New England : observations from the Shelfbreak PRIMER experiment (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2004. 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 109 (2004): C03006, doi:10.1029/2002JC001468.
    Description: In order to examine spatial and temporal variability of the shelfbreak front during peak stratification, repeated surveys using a towed undulating vehicle (SeaSoar) are used to describe the evolution of shelfbreak frontal structure during 26 July to 1 August 1996 south of New England. Spatial correlation (e-folding) scales for the upper 60 m of the water column were generally between 8 and 15 km for temperature, salinity, and velocity. Temporal correlation scales were about 1 day. The frontal variability was dominated by the passage of a westward propagating meander that had a wavelength of 40 km, a propagation speed of 0.11 m s−1, and an amplitude of 15 km (30 km from crest to trough). Along-front geostrophic velocities (referenced to a shipboard acoustic Doppler current profilers) were as large as 0.45 m s−1, although subject to significant along-front variations. The relative vorticity within the jet was large, with a maximum 0.6 of the local value of the Coriolis parameter. Seaward of the front, a small detached eddy consisting of shelf water was present with a diameter of approximately 15 km. Ageostrophic contributions to the velocity field are estimated to be as large as 0.3 m s−1 in regions of sharp curvature within the meander. These observations strongly suggest that during at least some time periods, shelfbreak exchange is nonlinear (large Rossby number) and dominated by features on a horizontal scale of order 10 km.
    Description: This work was performed under grants N-00014-95-1-0575 and N-00014-98-1-0059. as part of the ONR Shelfbreak PRIMER Initiative. Some additional analysis and writing was done under ONR grants N-00014-00-1-0931 and N-00014-01-1-0247.
    Keywords: Shelfbreak front ; Cross-shelf exchange ; Frontal dynamics
    Repository Name: Woods Hole Open Access Server
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  • 9
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    Buoyancy arrest and bottom Ekman transport. Part II : oscillating flow (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 40 (2010): 636-655, doi:10.1175/2009JPO4267.1.
    Description: The effects of a sloping bottom and stratification on a turbulent bottom boundary layer are investigated for cases where the interior flow oscillates monochromatically with frequency ω. At higher frequencies, or small slope Burger numbers s = αN/f (where α is the bottom slope, N is the interior buoyancy frequency, and f is the Coriolis parameter), the bottom boundary layer is well mixed and the bottom stress is nearly what it would be over a flat bottom. For lower frequencies, or larger slope Burger number, the bottom boundary layer consists of a thick, weakly stratified outer layer and a thinner, more strongly stratified inner layer. Approximate expressions are derived for the different boundary layer thicknesses as functions of s and σ = ω/f. Further, buoyancy arrest causes the amplitude of the fluctuating bottom stress to decrease with decreasing σ (the s dependence, although important, is more complicated). For typical oceanic parameters, arrest is unimportant for fluctuation periods shorter than a few days. Substantial positive (toward the right when looking toward deeper water in the Northern Hemisphere) time-mean flows develop within the well-mixed boundary layer, and negative mean flows exist in the weakly stratified outer boundary layer for lower frequencies and larger s. If the interior flow is realistically broad band in frequency, the numerical model predicts stress reduction over all frequencies because of the nonlinearity associated with a quadratic bottom stress. It appears that the present one-dimensional model is reliable only for time scales less than the advective time scale that governs interior stratification.
    Description: This research was sponsored by the National Science Foundation, Physical Oceanography Program through Grant OCE 0647050.
    Keywords: Ekman pumping/transport ; Buoyancy
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 10
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    Topographic rectification in a forced, dissipative, barotropic ocean (2011)
    Sears Foundation for Marine Research
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    Publication Date: 2022-05-25
    Description: Author Posting. © Sears Foundation for Marine Research, 2010. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 68 (2010): 337-368, doi:10.1357/002224010794657209.
    Description: Barotropic current rectification by topographic irregularities is treated for a case with bottom friction and fluctuating forcing. Geometries both with underlying shelf-slope topography and with no mean topographic slope are considered. In common with many previous studies of this sort, the resulting time-mean flow roughly follows isobaths in the direction that long topographic Rossby waves travel, but the mean flow often deviates locally from this rule. Further, as might be expected, there is an area-averaged correlation of pressure and bottom slope in the sense that would propel the mean flow. If the topographic irregularities have a length scale shorter than roughly a particle fluctuation excursion, then the typical along-isobath mean flow is proportional to the bottom slope, the irregularity length scale, the amplitude of the cross-isobath velocity fluctuations, and the inverse of the water depth. If the spatial scale of the irregularities is greater than roughly a particle excursion, then the resulting mean flow does not depend on irregularity length scale, but does depend on the Coriolis parameter, the bottom slope, cross-isobath velocity squared, the inverse depth and the inverse frequency squared. For large amplitude fluctuations, eddy momentum transport leads to a further inverse proportionality of mean flow to the strength of bottom friction. The overall mean flow parameterization holds only in a statistical sense (as opposed to point-by-point) because of the spatial complexity of typical flows. In a forced, dissipative system, the mean flow generation is often just tidal rectification (e.g., Loder, 1980) if the particle excursion is short relative to topographic scales. However, as the irregularity scale decreases, mean flow becomes weaker.
    Description: This work was sponsored by the Physical Oceanography Program at the National Science Foundation through grant OCE-0751731.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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