Abstract
Spiral bands are characteristic meso-beta-scale structures of typhoons in their mature stages. Observational study shows that spiral bands cause strong rainfall. The spiral bands are classified into two types: inner and outer rainbands. The inner rainband is formed near the typhoon center. In this study, we focus on the precipitation process in the inner rainband within the typhoon. Two neighboring spiral bands are often observed near the typhoon center. Previous studies have shown the mechanism of intensifying rainfall in the inner-side spiral band of two neighboring inner rainbands that frequently form in this region. However, the intensification of the outer-side spiral band of two neighboring inner rainbands has not been widely reported. Therefore, to clarify the mechanism of intensifying rainfall in the spiral bands, we focus on cloud microphysical processes and perform a numerical experiment using a cloud-resolving model. We show that cold rain processes are important for the intensification of precipitation in the spiral band. In particular, production and growth of graupel are the most effective processes for the intensification of precipitation in the spiral band.
