How Do the Convective and Microphysical Characteristics of Extreme Precipitation Over the Pearl River Delta at Monsoon Coast Vary With Increasing Rainfall Extremity?

Abstract

Using 5‐year dual‐polarization radar observations, variations of convective and microphysical characteristics of extreme precipitation features (EPFs) with increasing rainfall extremity over a monsoon coastal region (Pearl River Delta; PRD) in South China are investigated through comparing three groups of EPFs (ER1, ER2, and ER3). The more extreme rainfall shows a notable increase and decrease in the fractions of “intense” convection and “weak” convection, respectively. The higher rainfall extremity is accompanied by statistically significant increases in ice and liquid water contents but a roughly equal fraction of coalescence in liquid‐phase processes. While the raindrop size distributions of ER1 to ER3 similarly feature a mean size larger than “maritime‐like” droplets and a concentration much higher than “continental‐like” raindrops, the mean size and concentration of raindrops tend to increase slightly with the increasing rainfall extremity. Two sensitivity experiments on EFP definition confirm the robustness and representative of the above results.

Macro‐ and Microphysical Characteristics of Extreme Hourly Precipitation Over the Pearl River Delta on the Monsoon Coast (South China)

“…The major‐to‐minor axis ratios of the 20 dBZ and 40 dBZ regions are mostly (>95%) less than 3 (Figures 6c and 6d), with only 1%–3% and 2%–3%, respectively, meeting the criterion for linear convection (>4; Geerts, 1998). The non‐linear shapes of the CCs and their parent precipitation regions found in the extreme hourly precipitation agree with those in extreme instantaneous precipitation over the PRD (Gao23; Yu22). These results are qualitatively consistent with the previous finding in case studies (e.g., Zhang et al., 2022) and statistical analysis (Ng et al., 2022) that extreme rainfall‐producing convective systems in this monsoon coastal region usually occur in a deep moist layer with weak‐to‐moderate vertical wind shear (VWS), moving very slowly with convectively generated weak cold outflows (< about 5 m s −1 ).…”

“…The wide distribution of convective intensity in EHPAs is qualitatively similar to that in extreme instantaneous precipitation (Gao23; Yu22). However, the distributions of individual CC's convective intensity vary much less with the extreme level of hourly precipitation considered in this study compared to those in extreme instantaneous precipitation (cf.…”

“… Normalized occurrence frequency (unit: %) of median ΔZ h versus median ΔZ dr from 3 to 1.5 km in individual Convective Cores for EHPA_G1 to EHPA_G3 (this study; a–c) and Extreme Precipitation Features for EPF_G1 to EPF_G3 (Gao23; d–f). Red numbers represent the proportion (%) in each quadrant.…”

“…A sensitivity experiment using a different threshold of the intersection area to track the EHPAs and CCs supports robustness of the analysis results. The macro‐ and microphysical features of CCs are compared with those of the EPFs producing extreme instantaneous precipitation (Gao23). The major findings include the following: The EHPAs are mostly smaller than 10 km 2 with the mean area of <2 km 2 and tend to be more localized with more extreme hourly precipitation.…”

“…Y. Y. Gao et al (2023;Gao23 hereafter) found a substantial increase in the overlap between extreme convection and extreme rainfall when the extreme instantaneous rain rates increase from the 95th-to-99th percentiles (84-126 mm hr 1 ) to greater than the 99.9th percentile (186 mm hr 1 ). Huang et al (2023) also analyzed microphysical characteristics of extreme-rainfall convection over the PRD with a focus on sub-regional differences in the lightning flash rate during the pre-summer rainy season.…”