东天山哈密地区典型暴雨事件对流触发机制对比分析

本文选取2018年7月31日（简称“7.31”暴雨）和2016年8月8日（简称“8.8”暴雨）两次东天山哈密地区强降水天气过程，利用NCEP/NCAR的FNL资料（0.25°×0.25°）、中国地面卫星雷达三源融合逐小时降水产品、新疆地区常规观测资料、FY-2G卫星产品，通过对暴雨期间锋生函数计算诊断，证实了两次强降水过程中尺度对流系统触发因子差异，取得如下主要结果:（1）“7.31”暴雨期间，500 hPa西太平洋副热带高压位置异常偏北，700 hPa暖舌沿副高南侧偏东急流向西北伸展，低层增暖增湿，暴雨区上空形成不稳定大气层结，多个中尺度对流系统在700 hPa低空急流前生成，向东北方向移动和发展。“8.8”暴雨期间，500 hPa西太平洋副热带高压位置异常偏西，对流云团在对流层低层西南急流前生成向东北方向移动。（2）对流层低层暴雨区暖锋锋生是“7.31”暴雨中尺度对流云团的触发因子，云团初生阶段对流触发主要是锋生水平散度项和由垂直运动发展引起的倾斜项决定，成熟阶段暖锋锋生主要由锋生形变项和倾斜项所致。低空东南急流的维持加强利于锋面次级环流发展，是造成中尺度对流系统长时间维持的主要原因。（3）“8.8”暴雨对流云团由对流层低层弱冷锋触发。对流云团发展初始阶段，对流层低层冷锋锋生主要由水平辐散项决定；对流云团成熟阶段，对流层低层冷锋锋生主要由倾斜项决定。低层切变线长时间维持和加强利于低层冷锋进一步锋生，是造成中尺度对流系统长时间维持的主要原因。

Comparison of Convective Triggering Mechanisms of Typical Rainstorm Events in the Hami Area of East Tianshan Mountains

In this study, multiple data sources were used to conduct an in-depth analysis of two extreme rainfall events that occurred in the south-eastern Hami area on 31 July 2018 (hereinafter referred to as the “7.31” heavy rainstorm) and in the northern Hami area (Xinjiang, China) on 8 August 2016 (hereinafter referred to as the “8.8” heavy rainstorm). Based on the calculation of the frontogenesis function using the NCEP/NCAR FNL reanalysis (0.25°×0.25°) , the differences among the mesoscale convection trigger factors were compared and analyzed between the two heavy rainfall events. The following results were observed: (1) During the “7.31” heavy rainstorm, the 500-hPa western Pacific subtropical high was anomalously northerly and was westerly during the “8.8” heavy rainstorm; several mesoscale cloud clusters generated in front of the 700-hPa Hexi corridor jet stream during the “7.31” heavy rainstorm, and generated in front of the 700-hPa southwesterly jet stream during the “8.8” heavy rainstorm. (2) In “7.31” heavy rainstorm, the atmosphere was conditionally unstable over the region and had unstable convective energy triggered by warm frontogenesis at the low troposphere. Warm frontal frontogenesis was determined by the horizontal divergence and tilt term during convective initiation and by deformation and tilt terms while convection was mature. (3) During the “8.8” heavy rainstorm, the convective cloud clusters were triggered by cold frontogenesis at the low troposphere and then merged and developed along the 500-hPa steering flow. The atmosphere was conditionally unstable over the region and had unstable convective energy. Additionally, the maintenance and intensification of the 700-hPa shear line were in favor of the cold frontal frontogenesis. It was also the main responsibility for the long period of the mesoscale convective system. Cold frontal frontogenesis was determined by the horizontal divergence term during convective initiation and by tilt terms while convection was mature.