The MODE/POLYMODE experiments conclusively established that the ocean has an energetic mescoscale, which is a major contributor to the northward transport of heat and the mixing of salinity and other conserved properties. The early process models for the mesoscale emphasized long-lived isolated vortices. Flierl (1987) and Olsen (1991) present comprehensive reviews of these models. The ultimate examples of long-lived vortices are modons (Larichev and Reznik, 1976). Modons are exact solutions to the nonlinear Euler equations with both wave-like and vortex-like properties. All isolated vortex models share a common characteristic: a substantial amount of core fluid trapped by bounding surfaces of potential vorticity. Climatologically forced general circulation models also are consistent with the notion of long-lived mesoscale vortices containing a core of trapped fluid (e.g., Kantha et al., 2005). In contrast, we have studied mesoscale eddies in a variety of data assimilating models and have found that all exhibit considerable exchange between the eddy cores and the ambient fluid outside the eddies. A detailed blob calculation for one ring, Fourchon, from the Gulf of Mexico illustrates the leaky property. This calculation illustrates the fundamental dilemma: does data assimilation corrupt mesoscale processes, or does it delineate new physics? Both possibilites are assessed.

A.D. Kirwan, Jr. received an A.B. from Princeton University and a Ph.D. from Texas A&M University. He has held numerous research appointments with the federal government, the private sector and in academia. He was the Samuel L. and Fay M. Slover Chair of Physical Oceanography at Old Dominion University from 1987 to 1999 and is a plank owner for the Center for Coastal Physical Oceanography. Currently, he is the Mary A.S. Lighthipe Chair of Marine Studies at the University of Delaware. He has published approximately 100 refereed papers and is the author of Mother Nature's Two Laws: Ringmasters for Circus Earth and a co-editor of Rapid Environmental Assessment and Lagrangian Analysis and Prediction of Coastal and Ocean Dynamics.

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