[A-AS03] Advances in Tropical Cyclone Research: Past, Present, and Future

[AAS03-08] Precipitation Enhancement by Northward Ageostrophic Winds Associated with a Tropical Cyclone. --Cloud Resolving Simulation--

*Kazuo Saito^1,2,3, Takumi Matsunobu⁴, Tsutao Oizumi^2,3 (1.Atmosphere and Ocean Research Institute, the University of Tokyo, 2.Japan Meteorological Business Support Center, 3.Meteorological Research Institute , 4.Meteorologisches Institut, Ludwig-Maximilians-Universität)

Keywords:tropical cyclone, ageostrophic wind, pre-typhoon rainfall (PRE), cloud resolving model

In Japan, heavy rainfalls often occur when a typhoon exists off the south coast of Japan. These pre-typhoon rainfalls are also known in other countries and called as ‘PRE’. Saito (2019) examined the origin of observed northward winds for the case of T0918 (Melor) and showed that the ageostrophic winds are dynamically induced by the acceleration vectors of horizontal winds. Saito and Matsunobu (2020) conducted a numerical experiment with a horizontal resolution of 10 km and analyzed the northward moisture fluxes by the ageostrophic winds. They showed that PRE rainfalls over western Japan decreased substantially when the contributions in moisture fluxes by ageostrophic winds were removed. In this study, we perform simulations by a cloud resolving model with a horizontal resolution of 2 km to see the cloud microphysical aspects of precipitation enhancement by the upper-level moistening. Effect of the large-scale updraft induced by a secondary circulation of the ageostrophic winds on PRE is also investigated.



References:

Saito, K., 2019: On the northward ageostrophic winds associated with a tropical cyclone. SOLA, 15, 222-227.
Saito, K. and T. Matsunobu, 2020: Northward ageostrophic winds associated with a tropical cyclone. Part 2: Moisture transport and its impact on PRE. SOLA, 16, 198-205.