HR: 16:35h
AN: OS12C-03    [PDF]
TI: Nonlinear Gulf Stream interplay With the Deep Western Boundary Current: Observations and Model Results
AU: * Dietrich, D E
EM: dietrich@nmia.com
AF: AcuSea, Inc., 1421 Monte Largo Dr. NE, Albuquerque, NM 87112 United States
AU: Mehra, A
EM: mehra@erc.msstate.edu
AF: Geo Resources Institute, Mississippi State University Building 1103, Room 233, Stennis Space Center, MS 39529-6000 United States
AU: Haney, R L
EM: rlhaney@nps.navy.mil
AF: Department of Meteorology, Naval Postgraduate School, Monterey, CA 93943 United States
AU: Bowman, M J
EM: mbowman@notes.cc.synysb.edu
AF: School of Marine Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794-5000 United States
AU: Lai, C A
EM: cal@vega.lanl.gov
AF: Geoanalysis Group, EES_5, MS-D401 Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AB: Results from a two-way-coupled duo grid adaptation of the DieCAST ocean model to the North Atlantic/Gulf of Mexico/Caribbean Sea system are discussed, including animations. The model Deep Western Boundary Current (DWBC) strongly affects the Gulf Stream (GS) separation and path. Labrador-Sea-modified dense DWBC water arrives in the Grand Banks shelfbreak area after ~10 model years. Its arrival results in: GS separation near its observed Cape Hatteras separation location; GS path much closer to observations; offshore thermocline outcropping along an intense GS front; and relatively flat time mean isopycnals between strongly sloping GS and DWBC isopycnals. Such flattening is clearly seen in Yashayaev's non-diffused climatology, and indicates eddy dynamics characteristic of baroclinic instability rather than diffusive lateral mixing between the GS and DWBC. The wedge shaped region between the separated Gulf Stream and continental shelf slope is filled with eddies, including intense warm core eddies that pinch off the northern tips of Gulf Stream meanders. The flattened isopycnals in this region's interior, in both climatology and model results, suggests that the nonlinear eddy system is fueled at least partly by regional potential energy release because, by their very nature (in contrast to diffusive mixing), such potential energy releasing eddies act to REDUCE isopycnal slopes in the region's interior; the larger slopes at the region's boundaries are maintained by open boundary transports from outside the wedge shaped region. This is analagous to the nonlinear wave regime of the rotating annulus experiments, whose interior isotherms have significantly less slope than in more dissipative wave and axisymmetric regimes, while the larger slopes at the boundaries are maintained by conduction at the annular walls. The strikingly flat nature of the time mean interior isopycnals and strength of the eddies suggests that dissipation is small and that little potential energy release is needed to maintain the eddy energy. Based on these observations and model results, we suggest that climatologically important, eddy-available-potential-energy generating, cross-mean-isopycnal potential density transports are small, but concentrated near the edges of the wedge as a result of frontal eddies. The resulting potential energy release fuels the eddy field, which disperses the energy away from its frontal source regions. To simulate such climatologically important behavior, models must have realistically low dissipation. arrives in the Grand Banks shelfbreak area after ~10 model years. Its arrival results in: GS separation near its observed Cape Hatteras separation location; GS path much closer to observations; offshore thermocline outcropping along an intense GS front; and relatively flat time mean isopycnals between strongly sloping GS and DWBC isopycnals. Such flattening is clearly seen in Yashayaev's non-diffused climatology, and indicates eddy dynamics characteristic of baroclinic instability rather than diffusive lateral mixing between the GS and DWBC.
DE: 4520 Eddies and mesoscale processes
DE: 4528 Fronts and jets
DE: 4532 General circulation
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4576 Western boundary currents
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting