副热带高压控制下湖南两次短时暴雨发生及系统维持机制对比分析

利用地面自动站资料、多普勒天气雷达资料、卫星逐小时TBB资料及NCEP再分析资料，对2018年副高控制下湖南两次短时暴雨发生及维持机制进行分析。结果表明：①在水汽丰沛且有足够的不稳定能量和抬升条件下，强盛副高脊区反气旋环流内也可以触发短时暴雨天气，其大尺度环流形势特征和湖南典型暴雨过程有着较大差异；②对流性降水发生前，不稳定能量明显增强，中低层增湿明显，为暴雨提供能量与水汽条件；③两次过程分别受副高南侧热带气旋外围云系扰动和弱冷空气侵入影响，925 hPa形成弱扰动或者弱切变，配合地面中尺度辐合线，近地面动力抬升触发对流性降水，白天受太阳辐射影响，能够自由触发热对流。地形抬升也是重要触发机制，发生在迎风坡热对流占比84%；④两次短时暴雨的雷达回波为非常明显的低质心高效率的降水回波，环境风及其垂直风切变小，尽管不利于对流风暴有组织的发展，但雷暴单体移动缓慢，有利于同一地区长时间的强降水。

Comparative Analysis on Occurrence and Maintenance Mechanism of Two Short-Term Rainstorms in Hunan Province under Control of Subtropical High

Based on the ground automatic station data, doppler weather radar data, satellite hourly TBB data and NCEP reanalysis data, we analyze the occurrence and maintenance mechanism of two short term rainstorms in Hunan under the control of subtropical high in 2018. The results show that: (1) Under the condition of abundant water vapour and sufficient unstable energy and uplift, the short term rainstorm weather can also be triggered in the anticyclone circulation in the strong subtropical high ridge. Its large scale circulation characteristics are quite different from the typical rainstorm process in Hunan. (2) Before the occurrence of convective precipitation, the unstable energy was significantly enhanced. The humidification in the middle and lower layers was obvious, providing energy and water vapour conditions for the rainstorm. (3) The two processes were respectively affected by the disturbance of the outer cloud system of the tropical cyclone on the south side of the subtropical high and the intrusion of weak cold air. There was weak disturbance or weak shear forming at 925 hPa, cooperating with the ground mesoscale convergence line. Near surface dynamic uplift triggered convective precipitation. Affected by solar radiation during the day, it could freely touch heat convection. Topographic uplift was also an important trigger mechanism. Thermal convection occurred on the windward slope, accounting for 84%. (4) The radar echoes of two short term rainstorms were obvious precipitation echoes with a low centroid and high efficiency. The environmental wind and its vertical wind shear were small, which was not conducive to the organized development of convective storms. However, the thunderstorm monomer moved slowly, which was conducive to long term heavy precipitation in the same area.