2024年台风“格美”造成邵阳暴雨的成因分析

Analysis of the Causes of the Heavy Rainfall in Shaoyang Caused by Typhoon “Gaemi” in 2024

摘要: 台风“格美”残余环流在湖南省北部缓慢西移的过程中，给邵阳地区带来了大范围持续暴雨天气。使用常规观测资料及ERA5再分析资料，对台风“格美”残余环流导致邵阳地区暴雨的过程进行了分析。结果表明：(1) 邵阳暴雨区呈现“高层强上升(<−2 Pa/s)、中层下沉、低层弱上升”的分层特征。东北部暴雨依赖高层强上升运动与低层高湿(比湿q > 15 g/kg)、高热力不稳定(假相当位温${\theta }_{se}>356K$ )形成动力–湿度协同机制，降水持续时间长；西北部暴雨中心依赖“下暖湿–上干冷”不稳定层结，降水突发性强但持续时间较短。(2) 850 hPa水汽输送通道在暴雨区稳定维持，中心处水汽通量强度大于16 g/(cm·hPa·s)，东北侧暴雨发生前两至三个小时有显著的水汽辐合。(3) 东北侧暴雨中心上空存在明显的湿对称不稳定(MPV < 0且$\frac{\partial {\theta }_{se}}{\partial p}\le 0$ )与高层强上升运动协同增强对流的有序组织，形成持续性强降水；西北部暴雨中心仅表现为对流不稳定($\frac{\partial {\theta }_{se}}{\partial p}\le 0$ )，缺乏湿对称不稳定的协同作用，导致降水以短时强降水为主。

Abstract: As the remnants of Typhoon Gaemi slowly moved westward across northern Hunan Province, they brought widespread and persistent heavy rainfall to the Shaoyang region. Using conventional observational data and ERA5 reanalysis data, we analysed the process by which the remnants of Typhoon Gemi caused heavy rainfall in the Shaoyang region. The results indicate: (1) The Shaoyang heavy rainfall area exhibits a layered characteristic of “strong upward motion in the upper layers (<−2 Pa/s), sinking in the middle layers, and weak upward motion in the lower layers”. The heavy rainfall in the northeastern region relies on a dynamic-humidity synergy mechanism formed by strong upward motion in the upper layers, high humidity in the lower layers (specific humidity q > 15 g/kg), and high thermal instability (pseudo-equivalent potential temperature > 356 K), resulting in prolonged rainfall duration; The northwestern heavy rainfall centre relied on an unstable layer structure of “warm and humid below, dry and cold above”, resulting in sudden but short-lived precipitation. (2) The 850 hPa water vapour transport channel remained stable in the heavy rainfall area, with a water vapour flux intensity greater than 16 g/(cm·hPa·s) at the centre. Significant water vapour convergence occurred two to three hours before the onset of heavy rainfall in the northeastern region. (3) Above the northeastern heavy rainfall centre, there is a clear wet symmetric instability (MPV < 0 and $\frac{\partial {\theta }_{se}}{\partial p}\le 0$ ) that synergistically enhances convection with strong upper-level upward motion, forming sustained heavy rainfall; the northwestern heavy rainfall centre only exhibits convective instability ($\frac{\partial {\theta }_{se}}{\partial p}\le 0$ ) and lacks the synergistic effect of wet symmetric instability, resulting in precipitation primarily consisting of short-duration heavy rainfall.