This paper presents an analysis of the dominant cloud microphysical processes of the extreme rainfall event on 7 May 2017, using a series of convective-permitting simulations. Special emphasis is placed on the microphysical processes of two extreme-rain-producing storms, yielding hourly rainfalls exceeding 120 mm. For the Huashan (HS) storm, a large amount of cloud water is produced through condensation (PRW_VCD) within the storm, and significant rainwater is generated by the collection of cloud water by raindrops (PRR_RCW). As for the Jiulong (JL) storm, warm rain microphysical processes are as same as the HS storm. Additionally, considerable rainwater is produced via the collection of graupel by raindrops (PRR_RCG), with contributions also coming from the melting of graupel (PRR_GML). It is noteworthy that there is slight evaporation of raindrops (PRV_REV) in both storms. To verify the dominant cloud microphysical processes of the extreme rainfalls, an experiment has been conducted using a simple ice microphysics scheme that covers the aforementioned dominant microphysical processes. The results indicate that extreme rainfalls are well replicated with the simple microphysics scheme, showing good agreement in spatial distribution and temporal evolution with observations and the control run. The experiment confirms largely the dominant cloud microphysical processes responsible for the extreme rainfall. Based on the results, we propose that placing special emphasis on the treatment of snow terminal velocity in the Thompson scheme would improve the performance of the scheme for heavy rainfall simulation. The findings gained here may help further understand cloud microphysical processes for localized extreme rainfall over southern China, and provide guidance for the improvement of cloud microphysics schemes.

中文翻译：

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2017 年 5 月 7 日，对华南地区极端降雨风暴中主导云微物理过程的调查


本文使用一系列允许对流的模拟，分析了 2017 年 5 月 7 日极端降雨事件的主要云微物理过程。特别强调两次产生极端降雨的风暴的微物理过程，每小时的降雨量超过 120 毫米。对于华山 （HS） 风暴，暴风雨内部通过凝结 （PRW_VCD） 产生大量云水，雨滴 （PRR_RCW） 收集云水产生大量雨水。至于九龙 （JL） 风暴，暖雨微物理过程与 HS 风暴相同。此外，雨滴 （PRR_RCG） 通过收集霰会产生大量雨水，霰的融化 （PRR_GML） 也做出了贡献。值得注意的是，在两次风暴中都有轻微的雨滴蒸发 （PRV_REV）。为了验证极端降雨的主要云微物理过程，使用简单的冰微物理方案进行了一项实验，该方案涵盖了上述主要的微物理过程。结果表明，使用简单的微物理方案可以很好地复制极端降雨，在空间分布和时间演变方面与观测和对照运行具有良好的一致性。该实验在很大程度上证实了导致极端降雨的主要云微物理过程。基于这些结果，我们建议在 Thompson 方案中特别强调对雪终端速度的处理将提高该方案在强降雨模拟中的性能。 本研究结果可能有助于进一步理解华南地区局部极端降水的云微物理过程，为改进云微物理方案提供指导。