Breakdown of ITCZ-like PV Patterns

This study uses a shallow-water, normal-mode spectral model to examine the non-linear potential vorticity (PV) dynamics of the break¬down of both infinite an finite-length initial vorticity strips, simulating the inter-tropical convergence zone (ITCZ) found near the tropical eastern Pacific region. Irregularities in convection and diabatic heating are simulated using uniformly and randomly spaced pockets of enhanced vorticity as well as mass sinks embedded in otherwise uniform vorticity strips. Since the absolute vorticity divided by the fluid depth is materially conserved in the shallow water framework, analogies are drawn to the evolution of Ertel’s PV in a stratified fluid. Results indicate the spacing of vorticity pockets had a greater influence on the evolution of PV than did broadband perturbations of the vorticity strip boundaries; however, all results were consistent with linear stability theory. Finite length initial vorticity strips of uniform width had a greater tendency to break down into two PV pools while finite strips of non-uniform width did not. This may suggest the breakdown of elongated areas of PV into two circulation centers is more likely when ITCZ convection patterns are more uniform in width.