Stability of a cold core eddy in the presence of convection: Hydrostatic versus nonhydrostatic modeling

Geostrophic eddies in a stratified liquid are susceptible to baroclinic ins tabilities. In this paper, the authors consider these instabilities when su ch an eddy is simultaneously cooled homogeneously from above. As a linear s tability analysis shows, the developing convection modifies the background stratification, the stability boundaries, and the patterns of the dominant modes. The coupling between the effects of convection and the large-scale f low development of the eddy is studied through high-resolution numerical si mulations, using both nonhydrostatic and hydrostatic models. In the latter models, several forms of convective adjustment are used to model convection . Both types of models confirm the development of the dominant modes and in dicate that their nonlinear interaction leads to localized intense convecti on. By comparing nonhydrostatic and hydrostatic simulations of the flow dev elopment carefully, it is shown that convective adjustment may lead to erro neous small-scale variability. A simple alternative formulation of convecti ve adjustment is able to give a substantial improvement.