On Roles of ICE-Phase Microphysics in Tropical Cyclone Evolution with Vertical Wind Shear

Previous observational and numerical studies have shown ice-phase microphysics processes play a key role in precipitation distribution in Tropical Cyclones (TCs) by modulating sizes and fall speeds of hydrometeors. In addition, several cloud resolving numerical studies found that ice-phase microphysics can feed back on TC dynamics by releasing latent heating/cooling and changing water loading. Among these studies, simulations of a real TC with strong environmental vertical wind shear (EVWS) showed that ice-phase processes significantly facilitated TC intensification and precipitation, while idealized simulations without EVWS showed the contrary. It seems the EVWS may be the key to explain the contradiction in these findings . Therefore, possible impacts of the EVWS on roles of ice-phase in TC evolution need to be examined.

This study conducts idealized warm-rain and mixed-phase simulations of TCs with and without EVWS of 10m/s on an f-plane using the WRF3.2 (with finest horizontal resolution of 2km). Preliminary results show that TCs in warm-rain simulations reach significantly higher intensities than those in mixed-phase ones. In the mixed-phase simulations, the EVWS appears to have little destructive effect on TC intensity. In contrast, the EVWS in the warm-rain simulations significantly inhibits TC intensification. These results imply that the presence of EVWS may enhance (or weaken) the positive (or negative) impacts of ice-phase on TC intensification, but this effect may be not enough to explain the contradiction mentioned above. Future work will be focused on investigation of the mechanism of this effect. In addition, further numerical simulations will be conducted to test the sensitivity of these results to the magnitude of EVWS, specifications (size and tangential wind profile) of the initial TC vortex , lateral boundary conditions and microphysics schemes.