Data Assimilative Modeling Investigation of Gulf Stream Dynamics Along the U.S. East Coast Seaboard

Shun Mao, North Carolina State University, Department of Marine, Earth, and Atmospheric Sciences, Raleigh, United States, Ruoying He, North Carolina State University, Marine, Earth, and Atmospheric Sciences, Raleigh, United States, John Bane, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States, Glen Gawarkiewicz, Woods Hole Oceanographic Institution, Woods Hole, MA, United States and Robert E Todd, Woods Hole Oceanographic Institution, Physical Oceanography, Woods Hole, MA, United States
Abstract:
Boundaries between subtropical and subpolar oceanic gyres are characterized by confluent western boundary currents in the open ocean and convergence in the adjacent shelf and slope waters, which leads to large net export of shelf waters to the open ocean. However, complex, bidirectional shelf-open ocean exchange also occurs and is driven by variability in the adjacent western boundary currents, atmospheric forcing, and shelf water properties, and is influenced by local bathymetric characteristics. This study applies an advanced data assimilative ocean circulation model to hindcast the interaction between the Gulf Stream and the shelf and slope circulation along the U.S east coast seaboard. Using the strong constraint 4D Variational data assimilation algorithm, the model assimilates satellite sea surface height (SSH), sea surface temperature (SST), in situ temperature, and salinity profiles measured by expendable bathythermograph, Argo floats, shipboard CTD casts, and glider transects. Model validations against independent hydrographic data show significant error reductions in the data assimilative model prediction. It is found that the across-shelf transport receives a major influence from the Gulf Stream, the mean path of which is strongly influenced by the flow and topography Interaction. Associated time-averaged eddy fluxes are also essential to maintain and reshape paths of the Gulf Stream. Vorticity analysis further reveals that the nonlinear advection term, as well as the residual of joint effect of baroclinicity and bottom relief (JEBAR) and advection of potential vorticity (APV) play important roles in controlling the variability of the Gulf Stream vorticity.
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