Jovian Polar Vortex Generation in a Shallow-Water Model with Quasi-Stochastic Convection

Abstract

The mechanisms governing the formation and maintenance of polar vortices on Saturn and Jupiter represent a significant challenge in current planetary atmospheric dynamics. In the presence of internal heat sources, the existence of condensable components leads to widespread moist convection in the polar regions of these gas giants. However, the role of moist convective organization in the formation and maintenance of such polar vortices remains poorly understood. To investigate the interaction between convection and polar vortices, this study develops a polar $γ$-plane shallow-water model coupled with a quasi-stochastic convective parameterization. In this quasi-stochastic scheme, convection is prescribed as localized impulsive mass sinks, with the inception probability depending on local vorticity, thereby assigning a higher convective likelihood to cyclonic regions. Numerical experiments successfully reproduce shielded cyclones and persistent vortex crystals reminiscent of Jupiter's polar configuration. Increasing mesoscale feedback promotes vortex growth, shield formation, and spectral organization, while the characteristic vortex scale depends on both the deformation radius and the convective parameterization. The resulting patterns exhibit both clockwise and counterclockwise structural drift, whose direction and rate are not adequately captured by a conventional Rossby wave phase-speed estimate. A Biot--Savart diagnostic reveals competing contributions to structural drift, with predominantly counterclockwise advection induced by the other vortices and clockwise advection induced by the background vorticity outside the identified vortices. These results provide a possible formation pathway for shielded vortex crystals and highlight the role of convective feedback in vortex formation.