Cyclonic vortices on the tropopause are characterized by compact structure and larger pressure, wind and temperature perturbations when compared to broader and weaker anticyclones. Neither the origin of these vortices nor the reasons for the preferred asymmetries are completely understood; quasigeostrophic dynamics, in particular, have cyclone--anticyclone symmetry.
In order to explore these and related problems, we introduce a novel small Rossby-number approximation to the primitive equations applied to a simple model of the tropopause in continuously stratified fluid. This model resolves dynamics that give rise to vortical asymmetries, while retaining both the conceptual simplicity of quasigeostrophic dynamics and the computational economy of two-dimensional flows. The model contains no depth-independent (barotropic) flow, and thus may provide a useful comparison to 2D flows dominated by this flow component.
Vortex organizations as shown by snapshots in potential temperature for the sQG+1 (left, rossby number = 0.1) and sQG models (right) which begin from symmetric, random initial conditions. For sQG+1, the compact red ovals with white rings are intense cyclones, while the broader blue patches are relatively weaker anticyclones. The light blue background is indicative of sQG+1 surface cooling (warming for the tropopause case). For sQG, the vortex populations are statistically symmetric.
A New Surface Model for Cyclone-Anticyclone Asymmetry, with GJ Hakim & C Snyder