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On the Mean Dynamical Balances of the Gulf Stream Recirculation Zone,
NATIONAL CENTER FOR ATMOSPHERIC RESEARCH BOULDER CO
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The time mean circulation is analyzed at a site on the southern edge of the Gulf Stream Recirculation Zone 31 N, 70 W from data taken in the POLYMODE Local Dynamics Experiment. Additional mean quantities are described from a combination of dynamical assertions and inferences. The mean vorticity balance is examined to infer the mean vertical velocity and eddy relative vorticity flux divergence. The vertical velocity is found to be mostly upward and an order of magnitude larger than the downward surface Ekman pumping. In the mean heat, salt, density, and potential vorticity budgets, the mean advections of these quantities are non-zero, and substantial eddy flux divergences are again required for balance. These are inferred to be primarily associated wtih mesoscale eddies. The corresponding horizontal eddy diffusivities for these quantities are large approx. 10 billion sq cms over an extensive depth range, from the surface to at least 4000 m. As assessment is also made of the likelihood of a homogeneous potential vorticity layer in the Recirculation Zone. From our estimates of the local potential vorticity gradients, there is no clearly indicated zero gradient layer, and the qualitative features of our local estimates are consistent with the larger-scale analysis of McDowell et al. 1983.
APPROVED FOR PUBLIC RELEASE