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  • 1
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    A coastal current in winter : autonomous underwater vehicle observations of the coastal current east of Cape Cod (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C07030, doi:10.1029/2007JC004306.
    Description: Evolution of the coastal current structure on the shallow continental shelf east of Cape Cod was studied using autonomous underwater vehicle (AUV) surveys and moored observations during the winters of 2005 and 2006. A coastally bounded plume of relatively fresh water, characteristic of a coastal current, persisted throughout both winters despite strong mixing. Nondimensional parameter analysis classified the plume as a bottom-trapped gravity current over a moderately steep slope, placing it in the context of other buoyant coastal currents. The range of water properties within the coastal current, its spatial extent and temporal variability were characterized on the basis of the data from repeat hydrographic sections. Along-shore freshwater transport was dominated by highly variable barotropic flow driven by local wind and basin-wide pressure gradients. It eventually contributed substantially to the average southward along-shore freshwater transport, estimated at 1.1 ± 0.3 × 103 m3 s−1 in February and 1.8 ± 0.4 × 103 m3 s−1 in the first half of March 2006. The contribution of baroclinic buoyancy-driven freshwater transport was typically an order of magnitude lower during both winters. Despite the relative weakness of the baroclinic freshwater transport, the coastal current potentially had a major impact on water mass modification during the winter. Continual presence of the low-salinity plume prevented the formation of cold dense water near the coast and its export offshore. The coastal current effectively isolated the inner-shelf zone, reducing its potential role in ventilation of the intermediate layers of the Wilkinson Basin of the Gulf of Maine.
    Description: This work was supported by the Coastal Ocean Institute of the Woods Hole Oceanographic Institution and the WHOI SeaGrant Office under grant NA06OAR4170021. G.G. was supported by the Office of Naval Research as part of the AWACS program under grant N00014-05-1-0410. A.S. was supported, in part, by WHOI Post-Doctoral Scholarship.
    Keywords: Coastal current ; Cooling ; Autonomous underwater vehicle
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Offshore transport of shelf waters through interaction of vortices with a shelfbreak current (2013)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 905–919, doi:10.1175/JPO-D-12-0150.1.
    Description: Interactions between vortices and a shelfbreak current are investigated, with particular attention to the exchange of waters between the continental shelf and slope. The nonlinear, three-dimensional interaction between an anticyclonic vortex and the shelfbreak current is studied in the laboratory while varying the ratio ε of the maximum azimuthal velocity in the vortex to the maximum alongshelf velocity in the shelfbreak current. Strong interactions between the shelfbreak current and the vortex are observed when ε 〉 1; weak interactions are found when ε 〈 1. When the anticyclonic vortex comes in contact with the shelfbreak front during a strong interaction, a streamer of shelf water is drawn offshore and wraps anticyclonically around the vortex. Measurements of the offshore transport and identification of the particle trajectories in the shelfbreak current drawn offshore from the vortex allow quantification of the fraction of the shelfbreak current that is deflected onto the slope; this fraction increases for increasing values of ε. Experimental results in the laboratory are strikingly similar to results obtained from observations in the Middle Atlantic Bight (MAB); after proper scaling, measurements of offshore transport and offshore displacement of shelf water for vortices in the MAB that span a range of values of ε agree well with laboratory predictions.
    Description: Laboratory work was supported by the National Science Foundation through Grant OCE- 0081756. Glider observations in March–April 2006 were supported by the National Science Foundation through Grant OCE-0220769. Glider observations in July– October 2007 were supported by a grant from Raytheon. RET was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Cooperative Institute for the North Atlantic Region. The REMUS observations were funded by the Office of Naval Research. GGG was supported by the National Science Foundation through Grant OCE-1129125 for analysis and writing.
    Description: 2013-11-01
    Keywords: Continental shelf/slope ; Eddies ; Fronts ; Transport ; Laboratory/physical models
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Length scale of the finite-amplitude meanders of shelfbreak fronts (2015)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2598–2620, doi:10.1175/JPO-D-14-0249.1.
    Description: 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.
    Description: WGZ and GGG were supported by the National Science Foundation through Grant OCE-1129125.
    Description: 2016-04-01
    Keywords: Circulation/ Dynamics ; Instability ; Ocean circulation ; Topographic effects ; Atm/Ocean Structure/ Phenomena ; Fronts ; Models and modeling ; Numerical analysis/modeling
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    A coastal current in winter : 2. Wind forcing and cooling of a coastal current east of Cape Cod (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2008. 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 113 (2008): C10014, doi:10.1029/2008JC004750.
    Description: The combined effect of cooling and wind-driven buoyancy flux (WDBF) on a buoyant coastal current east of Cape Cod is investigated using observations and process-oriented numerical modeling. Theoretical considerations show that with the moderately strong surface density gradients observed in the Outer Cape Cod Coastal Current, WDBF can substantially exceed the buoyancy loss due to cooling, especially during intense winter storms. Evidence of deep convection associated with strong negative WDBF during downwelling-favorable winds is clearly seen in the moored observations. A simplified two-dimensional numerical model is used to illustrate the evolution of wind- and buoyancy-driven cross-shelf overturning circulation in response to surface cooling and episodic storm events. The simulation confirms that WDBF plays an important role in driving subduction of cold surface water at the offshore surface outcrop of the coastal current font. The presence of the coastal current is also shown to block onshore Ekman transport. As a result, the downwelling circulation in a cross-shore plane is predicted to have a complex multicell structure, in which exchange between the inner shelf and midshelf is restricted. The downwelling circulation has a major impact on the cross-shelf origin of cold, dense shelf waters contributing to intermediate layers of the Wilkinson Basin of the Gulf of Maine.
    Description: This work was supported by the Coastal Ocean Institute of the Woods Hole Oceanographic Institution and the WHOI SeaGrant Office under grant NA06OAR4170021. G.G. was supported by the Office of Naval Research as part of the AWACS program under grant N00014-05-1-0410. A.S. was supported, in part, by WHOI Post-Doctoral Scholarship.
    Keywords: Coastal current ; Wind-driven buoyancy flux (WDBF) ; Cooling
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Horizontal scales of variability over the Middle Atlantic Bight shelf break and continental rise from finescale observations (2013)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 222–230, doi:10.1175/JPO-D-12-099.1.
    Description: Observations with fine horizontal resolution are used to identify the horizontal scales of variability over the Middle Atlantic Bight (MAB) shelf break and continental rise. Spray gliders collected observations along two alongshelf transects over the continental rise in March–April 2006 and along 16 cross-shelf transects over the shelf break and continental rise during July–October 2007. Horizontal resolution varied from 1 km or finer over the shelf to 6 km in deep water. These observations allow horizontal thermohaline variability offshore of the MAB shelf break to be examined for the first time. Structure functions of temperature and salinity, the mean square difference between observations separated by specified distances, reveal the horizontal spatial scales in the region. Exponential (e-folding) scales of temperature and salinity increase from 8–13 km near the shelf break to about 30 km over the continental rise. Just offshore of the shelf break, alongshelf structure functions exhibit periodicity with a 40–50-km wavelength that matches the wavelength of shelfbreak frontal meanders. Farther offshore, alongshelf structure functions suggest a dominant wavelength of 175–250 km, but these scales are only marginally resolved by the available observations. Examination of structure functions of along-isopycnal salinity (i.e., spice) suggests that interleaving of shelf and slope water masses contributes most of the horizontal variability near the MAB shelf break, but heaving of isopycnals is the primary source of horizontal variability over the continental rise.
    Description: Glider observations in March–April 2006 were supported by the National Science Foundation through Grant OCE-0220769. Glider observations in July–October 2007 were supported by a grant from Raytheon. RET was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Cooperative Institute for the North Atlantic Region. GGG was supported by the National Science Foundation under Grant OCE-1129125.
    Description: 2013-07-01
    Keywords: Continental shelf/slope ; North Atlantic Ocean ; Fronts ; In situ oceanic observations ; Profilers, oceanic
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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