Subseasonal Variations of Convective and Microphysical Characteristics of Extreme Precipitation Over the Pearl River Delta at Monsoon Coast

Abstract

AbstractThe large‐scale flows and rainfall pattern change markedly with the progression of the summer monsoon, but how the convective and microphysical characteristics of monsoon extreme precipitation vary subseasonally remains elusive. This study compares 16,844 extreme precipitation features (EPFs) among the pre‐monsoon, active‐monsoon, post‐monsoon periods, and tropical cyclone (TC) days using multisource data including dual‐polarimetric radar observations over the Pearl River Delta in South China. Results indicate that the environmental dynamics and thermodynamics significantly influence the EPFs' convective and microphysical properties. Despite the similar environmental conditions such as abundant moisture and moderate to large convective available potential energy (CAPE) under which the EPFs occur, differences among the four periods are noticed. During the pre‐monsoon period, precipitation systems are the largest in area but their EPFs are the least frequent and have the lowest raindrop concentration, likely due to the colder and drier environment with large vertical wind shear (VWS). The onset of the summer monsoon increases both the frequency and the convective intensity of EPFs, leading to an increase in raindrop size, which is consistent with the substantial increases of CAPE and moisture during the active‐monsoon period. The EPFs share similar convective intensity and raindrop size distribution (RSD) between the post‐monsoon and the active‐monsoon periods, although the post‐monsoon EPFs are slightly less frequent and have a smaller horizontal scale related to the reduced 0–6‐km VWS. Interestingly, EPFs associated with TCs have the weakest convective intensity but the most active warm‐rain processes with the RSD being closer to the maritime regime.