Formation of tropical cyclone spiral rainbands in idealized numerical simulations

Spiral rainbands are curved patterns of clouds and precipitation outside of the inner-core region of tropical cyclones (TCs). These features are often the source of various TC-related threats, such as flash flooding, landslides, and tornadoes. Their appearance in satellite imagery is often used to estimate TC intensity. Moreover, previous studies suggest that examining spiral rainbands can help understand changes in TC intensity.

Numerous ideas have been proposed to explain the formation of TC rainbands. Some of these hypotheses characterize rainbands as inertia-gravity waves or vortex-Rossby waves that emanate from the TC inner core. Other studies suggest that rainbands form through mechanical lifting mechanisms, similar to tropical squall lines. Despite these and many other efforts, there is still no widespread agreement in the literature about how TC spiral rainbands form. This study approaches the problem by conducting a series of numerical experiments in the context of radiative-convective equilibrium. High-resolution TC simulations are performed using the three-dimensional, cloud-permitting System for Atmospheric Modeling. The simulations are run at fixed sea-surface temperature with interactive radiation and surface fluxes. Preliminary insights into the role of inertia-gravity waves, vortex-Rossby waves, and mechanical lifting in TC rainband formation in this idealized setup are discussed.