研究已发现二级地形是中尺度对流的多发地，对下游强对流天气具有较大影响，然而二级地形对流的初生机制，以及二级地形在对流初生中的热、动力作用尚不清楚。申请人在已取得相关研究成果基础上，继续开展暖季长江中游地区二级地形对流的初生机制，以及二级地形动、热力作用对对流初生的影响机理研究。首先，依据已有中尺度对流系统的识别和统计结果，本项目拟进一步统计2000-2018年暖季二级地形上中尺度对流过程，使用多种观测资料，筛选出地面和高架对流的典型个例，深入对比分析两类对流的地面环境特征和低层大气环境条件，并揭示其差异。根据两类对流初生的环境特征，通过高分辨率数值模拟试验，深入研究二级地形地面和高架对流的具体触发过程及主要影响因子，以及二级地形的热、动力作用对对流初生的影响机制，并对比其在地面和高架对流初生机制的异同。通过本研究可以为二级地形对流初生机制的相关研究和对流初生的预报提供有益的参考。

Recent research found that mesoscale convective systems (MCSs) always occur over the second-step terrain and could have great impact on the heavy rainfall over the downstream regions. However, convection initiation (CI) of these convective systems are still unclear. Based on the relative results, this project plans to further study the CI over the second-step terrain along the middle reaches of Yangtze River during warm seasons and the dynamic and thermal effect of the second-step terrain on the CI. Firstly, according the current statistical results of MCSs, the MCSs over the second-step terrain during the warm seasons between 2000 and 2018 will be further recognized. Combing the analysis from multiple observation data, the surface-based and elevated convections will be selected. The differences of the surface features and low-level ambient conditions will be compared. According to observation analysis, the real and semi-ideal high resolution numerical simulations will be designed to further study the CI mechanisms and main factors of the two-type convections. Then, sensitive simulations will be implemented to investigate the dynamical and thermal effect of the second-step terrain on CI of the two-type convections. This study will provide positive references for the related research and severe weather forecasting over and east of the second-step terrain.