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Microphysical Characteristics of Extreme-Rainfall Convection over the Pearl River Delta Region, South China from Polarimetric Radar Data during the Pre-summer Rainy Season

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Abstract

During the pre-summer rainy season, heavy rainfall occurs frequently in South China. Based on polarimetric radar observations, the microphysical characteristics and processes of convective features associated with extreme rainfall rates (ERCFs) are examined. In the regions with high ERCF occurrence frequency, sub-regional differences are found in the lightning flash rate (LFR) distributions. In the region with higher LFRs, the ERCFs have larger volumes of high reflectivity factor above the freezing level, corresponding to more active riming processes. In addition, these ERCFs are more organized and display larger spatial coverage, which may be related to the stronger low-level wind shear and higher terrain in the region. In the region with lower LFRs, the ERCFs have lower echo tops and lower-echo centroids. However, no clear differences of the most unstable convective available potential energy (MUCAPE) exist in the ERCFs in the regions with different LFR characteristics. Regardless of the LFRs, raindrop collisional coalescence is the main process for the growth of raindrops in the ERCFs. In the ERCFs within the region with lower LFRs, the main mechanism for the rapid increase of liquid water content with decreasing altitude below 4 km is through the warm-rain processes converting cloud drops to raindrops. However, in those with higher LFRs, the liquid water content generally decreases with decreasing altitude.

摘 要

华南前汛期强降雨频发. 基于双偏振雷达观测, 本文研究了具有极端降水率的对流系统 (ERCF) 的微观物理特征及过程. 在极端降水对流系统发生高频区, 闪电频率表现出明显的区域性分布差异特征. 在闪电频率较高的子区域, 极端降水对流系统在冻结层以上具有更大体积的强反射率因子, 对应更活跃的淞附过程. 此外, 该区域的极端降水对流系统表现出更强的对流组织性和更大的空间覆盖范围, 这与该地区更强的低层风切变和更高的地形有关. 在闪电频率较低的子区域, 极端降水对流系统的回波顶和回波质心的高度更低. 在上述两个不同闪电频率的子区域, 极端降水对流系统发生时对应的最不稳定的对流有效位能 (MUCAPE) 并没有显著差异. 无论闪电频率高低, 碰并过程是极端降水对流系统中雨滴生长的主要机制. 在闪电频率较低的子区域, 极端降水对流系统的液态水含量在4公里高度以下随着海拔高度降低而迅速增加, 其主要机制是通过暖雨过程将云滴转化为雨滴. 然而, 在闪电频率较高的子区域内, 极端降水对流系统的液态水含量通常随着海拔高度的降低而减少.

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Acknowledgements

The authors would like to thank the scientists and engineers working on Guangzhou S-POL, the south-China ENTLS, the ERA5 reanalysis, and the DMSP/OLS nighttime light dataset. The DMSP/OLS nighttime light dataset can be downloaded at https://www.ngdc.noaa.gov/eog/dmsp/downloadV4composites.html. The extreme-rainfall convective feature data-set used in this work is available at https://doi.org/10.5281/zenodo.6331267. This work is primarily supported by the National Natural Science Foundation of China (Grant Nos. 42025501, 41905019, and 61827901) and the National Key Research and Development Program of China (Grant 2018YFC1506404 and Grant 2017YFC1501703). The authors also thank Dr. Haonan CHEN (CSU) and Prof. Anning HUANG (NJU) for their suggestions on this work.

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Correspondence to Kun Zhao.

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Article Highlights

• Clear differences in microphysics of the extreme-rainfall convective features found in regions with different lighting flash rates.

• Stronger low-level wind shear and higher terrain may favor the organization and ice processes of the extreme-rainfall convection.

This paper is a contribution to the special issue on the 14th International Conference on Mesoscale Convective Systems and High-Impact Weather.

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Huang, H., Zhao, K., Chan, J.C.L. et al. Microphysical Characteristics of Extreme-Rainfall Convection over the Pearl River Delta Region, South China from Polarimetric Radar Data during the Pre-summer Rainy Season. Adv. Atmos. Sci. 40, 874–886 (2023). https://doi.org/10.1007/s00376-022-1319-8

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  • DOI: https://doi.org/10.1007/s00376-022-1319-8

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