Ours is a theoretical/numerical study aimed at the question of whether local baroclinic instability can contribute to the generation of the mesoscale eddy fields of mid-ocean gyres. Our main tool is a two-layer, dissipative, quasi-geostrophic model forced by an imposed, horizontally homogeneous mean shear flow. In contrast to previous studies, we find that equilibrated flat-bottom eddy fields can contain roughly equal amounts of energy in the barotropic and baroclinic modes, in agreement with observations, as long as the layer depths are unequal. Thus, the nonuniform stratification of the ocean appears to play a major role in determining the baroclinicity of the ocean eddy field. We also find that nonzonal mean flows, which are ubiquitous in the ocean, can support eddy fields with rms velocities order ten times greater than the mean even when the vertical shear is as little as 1 cm per second, and planetary beta is present. Thus, our preliminary results indicate that a substantial amount of the eddy energy in the mid-ocean may be generated locally in the weak mean currents of the interior.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics