华南前汛期一类暖区暴雨系统组织机理及山地对其作用研究

The heavy rainstorms and extraordinary rainstorms occurring during the pre-summer flood period in South China are primarily warm sector rainstorms as shown in the field experiments of South China rainstorms. The severe rainfall produced by organized warm sector rainstorms can more easily cause various serious disasters such as floods and debris flows. Thus, the organized warm sector rainstorm with poor predictability is one of the major concerns in China. So far, the organized warm sector rainstorms occurring over the region around Guangxi and near the border area between Guangdong and Guangxi, which show significantly different characteristics from those occurring at the coastal regions of Guangdong, have been seldom investigated and not well understood. Therefore, the organized warm sector rainstorms occurring around Guangxi and near the border area between Guangdong and Guangxi during the pre-summer flood period, as well as the main weather systems influencing them, will be investigated in this project by using the statistical analysis of the multi-year high-resolution observations. The high-resolution numerical simulation of a typical case therein is then carried out with a meso-scale numerical model to diagnose its mechanisms involved, including the organization form of the convective system, and the rebirth and development of the convective cells. Finally, we intend to obtain the key environmental factors that significantly favor the role of mountains in promoting the organization process of warm sector rainstorm systems, and uncover the involved mechanism, based on the observational analyses and the comparative analyses of numerical experiments. This project aims to improve the understanding of the formation and development of the organized warm sector rainstorms around Guangxi and near the border between Guangdong and Guangxi during the pre-summer flood period and provide some scientific bases for its prediction.

华南暴雨外场试验表明华南前汛期大暴雨和特大暴雨主要是暖区暴雨，其中组织性暖区暴雨更容易造成洪涝和泥石流等重大灾害，是我国暴雨研究热点和预报难点之一。相比于广东沿海，广西和两广交界的前汛期暖区暴雨组织过程呈现出明显不同的特征，过去却很少对其进行研究，认识存在明显不足。鉴于此，本项目首先利用多年高分辨率观测资料，分析广西和两广交界的前汛期暖区暴雨系统的组织特征及其影响系统特征。在此基础上，结合高分辨率数值模拟，诊断分析主要影响系统作用下广西和两广交界地区暖区暴雨系统的组织机制，包括对流系统组织形态形成的原因，以及对流单体在组织过程中的再生和发展机制。最后，通过观测分析和数值试验揭示有利于广西和两广交界山地促进暖区暴雨系统组织过程的关键环境特征以及其中的促进机制。通过上述研究，提高人们对华南前汛期广西和两广交界的组织性暖区暴雨发生发展演变规律的科学认识，并为其预报提供一些科学思路。

华南前汛期大暴雨和特大暴雨主要是暖区暴雨，其中组织性暖区暴雨更容易造成洪涝和泥石流等重大灾害。相比于广东沿海，广西和两广交界的前汛期暖区暴雨组织过程呈现出明显不同的特征，过去却很少对其进行研究，认识存在明显不足。鉴于此，本项目通过多年（2011-2017）华南前汛期的高分辨率观测资料和再分析资料分析和典型个例数值模拟，研究了广西和两广交界的前汛期组织性暖区暴雨过程。结果显示广西和两广交界组织性暴雨事件主要发生在双低空急流和低空反气旋形势下。在双低空急流形势下，暖区暴雨系统往往与急流轴重叠，对流单体的触发地点分布沿向和其移动方向一致，暖区暴雨系统呈现为长距离的前向组织特征。在低空反气旋形势下，内陆北风和沿岸东南风在两广交界山地辐合并稳定维持，暖区暴雨系统整体上呈现为准静止的组织发展特征。对比分析结果显示两广交界山地对暖区暴雨系统的组织过程有明显的作用。一方面，两广交界山地的热力效应促使沿岸东风转向东南风，山地继而阻挡东南风，使得东南风与内陆北风在山地辐合，有利于暖区暴雨系统沿山地触发和维持。另一方面，两广交界山地可以促使暖区暴雨系统产生的下沉运动沿着山地重新分布，从而激发沿山地分布的暖区暴雨系统。此外，研究过程中揭示了一种有利于华南暖区暴雨系统转向移动的天气形势，并阐明了其作用机理和成因。通过上述研究，提高了对华南前汛期广西和两广交界的组织性暖区暴雨发生发展演变规律的科学认识，并为其预报提供一些科学思路。