The Sensitivity of Eyewall Instability to Microphysical Processes

Tropical cyclone eyewalls that develop a peak in the radial profile of potential vorticity (PV) may experience an instability that produces mixing between the eye and eyewall. This instability may also generate eyewall mesovortices and have longer-term consequences on the low-level wind field. Numerical modeling studies that have explored the impact of eyewall convection on the development of this instability have taken one of two approaches. The first is to consider only dry dynamics and approximate convection via an artificial heat source that mimics diabatic effects. The second has been to include moist processes, but to date only relatively simple microphysics parameterizations have been utilized. Since the inner-core PV structure of tropical cyclones is strongly influenced by latent heating within the eyewall, the representation of cloud microphysical processes will likely impact the radial PV profile and the growth of eyewall instability.

This study will use a cloud-resolving model to examine the sensitivity of eyewall instability and breakdown to microphysical processes. Numerical experiments will investigate the impact of mixed-phase vs. liquid-only microphysics as well as the impact of single vs. double-moment parameterizations. Not only will the initial growth rate of the instability be analyzed, but also the long-term consequences to tropical cyclone structure—including changes to the wind and precipitation fields.