Mesoscale and Microphysical Characteristics of a Double Rain Belt Event in South China on May 10-13, 2022.

A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China, leading to heavy precipitation. We examined the differences in the mesoscale characteristics and microphysics of the frontal and warm sector rain belts that occurred in South China on May 10-13, 2022. The southern rain belt occurred in an environment with favorable mesoscale conditions but weak large-scale forcing. In contrast, the northern rain belt was related to low-level horizontal shear and the surface-level front. The interaction between the enhanced southeasterly winds and the rainfall-induced cold pool promoted the persistent growth of convection along the southern rain belt. The convective cell propagated east over the coastal area, where there was a large temperature gradient. The bow-shaped echo in this region may be closely related to the rear-inflow jet. By contrast, the initial convection of the northern rain belt was triggered along the front and the region of low-level horizontal shear, with mesoscale interactions between the enhanced warm-moist southeasterly airflow and the cold dome associated with the earlier rain. The terrain blocked the movement of the cold pool, resulting in the stagnation of the frontal convective cell at an early stage. Subsequently, a meso-γ-scale vortex formed during the rapid movement of the convective cell, corresponding to an enhancement of precipitation. The representative raindrop spectra for the southern rain belt were characterized by a greater number and higher density of raindrops than the northern rain belt, even though both resulted in comparable hourly rainfalls. These results help us better understand the characteristics of double rain belts over South China. [ABSTRACT FROM AUTHOR]