CYCLONE-ANTICYCLONE ASYMMETRY IN THE MERGING PROCESS

Numerical experiments on the merging of baroclinic ageostrophic cyclon es and anticyclones are presented. The Miami, isopycnic-coordinate, sh allow-water model is used in a two-equal-layer version. The vortices a re defined in the upper layer as two circular patches of uniform relat ive vorticity with Rossby number Ro of order unity, and the bottom lay er is initially at rest. The initial interface deviation stems from an intermediate model accurate to the first order in Ro. Qualitatively, the same dependence of the merging on stratification as in previous qu asigeostrophic experiments is found. A repulsion (hetonic) effect oppo ses an attraction interface deviation effect in a competitive process that depends on the ratio between the vortices' lengthscale and the fi rst internal Rossby radius. However, noticeable differences appear bet ween cyclones and anticyclones. For strong and intermediate stratifica tion, the merging tendency for cyclones is greater than for anticyclon es. In the weakly stratified regime, it is observed that the repulsion hetonic effect is stronger for cyclones than for anticyclones. These differences are, in part, related to the initial interface deviation, which is always greater for cyclones than for anticyclones.