HR: 0830h
AN: OS21C-1141    [PDF]
TI: Progress in Modeling the Gulf Stream in a Duo Grid North Atlantic Ocean/Caribbean Sea/Gulf of Mexico model
AU: Mehra, A
EM: mehra@gri.msstate.edu
AF: Geo Resources Institute Mississippi State University, Bldg. 1103, Rm. 233, Stennis Space Center, MS 39529 United States
AU: * Dietrich, D E
EM: dietrich@nmia.com
AF: AcuSea Inc., 1421 Monte Largo Dr., N.E., Albuquerque, NM 87112 United States
AU: Haney, R L
EM: rlhaney@nps.navy.mil
AF: Department of Meteorology Naval Postgraduate School, 589 Dyer Road, Room 254, Monterey, CA 93943 United States
AU: Bowman, M J
AF: Marine Sciences Research Center Stony Brook University, Endeavour Hall, Room 215, Stony Brook, NY 11794 United States
AU: Lai, C A
AF: Geoanalysis Group Los Alamos National Laboratory, EES-5, Mail Stop D401, Los Alamos, NM 87545 United States
AB: The DieCAST ocean model is applied to the combined North Atlantic Ocean, Caribbean Sea and Gulf of Mexico, using two two-way coupled grids between 10 deg N and 75 deg N. Open boundary conditions derived from a one degree resolution global adaptation of DieCAST are applied at 10 deg N. Climatology based open conditions are applied at 75 deg N and combined with a northern sponge layer. The two grid resolutions are: 1/2 deg east of 60 deg W; and 1/6 deg west of 60 deg W. Vertical resolution is 30 levels. Annual cycle wind stress climatology and surface heat and freshwater fluxes are applied at the surface. The fluxes are derived from surface temperature and salinity climatology, using no unphysical transient damping (restoring toward climatology). The derived fluxes are such that the model multi-year {\it ensemble mean annual cycle} matches the observed surface annual cycle climatology. An idealized shelfbreak near the open northern lateral boundaries avoids unphysical vortex stretching effects caused by conventional vertical walls. Using annual cycle Hellerman wind stress climatology, the model results give: correct Gulf Stream (GS) separation and path; vigorous transients including cold- and warm-core GS rings; and a steep front in the Denmark Strait between a northward flowing fragment of North Atlantic Gyre water near Iceland and southward flowing East Greenland Current that feeds into the Deep Western Boundary Current (DWBC). The model DWBC strongly affects the GS separation and path. Labrador-Sea-modified dense DWBC water arrives in the Grand Banks shelfbreak area after $\sim$ 10 model years, leading to: GS separation and path much closer to observations; offshore thermocline outcropping along an intense GS front; and relatively flat time mean isopycnals between the 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: 3220 Nonlinear dynamics
DE: 4520 Eddies and mesoscale processes
DE: 4532 General circulation
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4576 Western boundary currents
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting