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2002 LAPCOD Meeting
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Dynamical/Thermodynamical Analysis of Upper-Limb Pathways of the Atlantic Meridional Overturning Circulation Using Synthetic Floats
George R. Halliwell, Jr., Robert H. Weisberg
MPO/RSMAS, University of Miami
ghalliwell@rsmas.miami.edu(Abstract received 09/27/2002 for session B)
ABSTRACT
Synthetic floats are released in an ocean model (HYCOM) to study three-dimensional fluid pathways followed by the upper limb of the meridional overturning circulation in the tropical/subtropical Atlantic. An analysis of 7200 floats released in the Southern Hemisphere is performed to demonstrate the importance of, and to quantify dynamical and thermodynamical processes that control, fluid paths extending into the interior subtropical North Atlantic. Vorticity constraints force upper limb water to approach the equator from the south within a predominantly inertial western boundary layer, and then require equatorial processes (inertial boundary layer dynamics, upwelling, heating) to reset water properties and permit the fluid to cross the equator. This typically requires eastward retroflection into the Equatorial Undercurrent. After upwelling at the equator, fluid either advects northward into the interior or westward along the equator to the western boundary. The latter fluid turns northward in a predominantly frictional western boundary (Munk) layer. The generation of negative relative vorticity then breaks the boundary layer constraints and permits retroflection of a substantial fraction of this fluid into the eastward NECC near 5°N from late spring through fall. Much of this fluid advects northward in the Ekman wind drift during the subsequent winter to the southern subtropical gyre, being governed by surface boundary layer dynamics en-route. There the fluid subducts and advects southwestward, governed by layered thermocline dynamics with superimposed time dependent planetary wave variability, eventually entering the westward NEC into the Caribbean Sea. It is necessary to use Lagrangian floats advected by all three velocity components to properly track upper-limb pathways.
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2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000