Convectively Coupled Linear Instability in TC-like Vortices

Asymmetric structures, such as spiral rainbands and polygonal eyewalls are critical to changes in the structure and intensity of a tropical cyclone (TC). Some studies suggest that inner rainbands and polygonal eyewalls are associated with vortex Rossby-waves, while others suggest that the asymmetries might be related to the instabilities of inertia-Gravity wave radiation from a Rossby-like wave in the vortex core. Although there are some evidences from simulations showing the convectively coupled features of vortex Rossby-waves, most of the theoretical frameworks are based on pure dry dynamics or dry dynamics forced by diabatic heating.

In our work, we first systematically investigated the characteristics of the asymmetries of simulated hurricanes, and their convectively coupled features and structures based on space-time power spectral analysis of an ensemble of WRF simulations. From there, we made the connection between the asymmetric structures in TCs and other well-studied convectively coupled waves, such as the equatorial waves. Furthermore, we will introduce our theoretical framework, where we incorporate a simple two-mode convective parameterization (Kuang, 2008) into the linearized primitive equations with a TC-like background vortex and heating profile. We will show that strong instabilities can arise from this model, and the structures of unstable normal modes resemble those from the simulations.