伊犁河谷一次区域性暴雨天气分析

Analysis of a Regional Rainstorm in the Ili River Valley

摘要: 本文利用常规观测资料、雷达资料，分析了伊犁河谷2024年8月18日白天至夜间的一场区域性暴雨天气过程。结果表明：暴雨发生时伊犁河谷500 hPa受西西伯利亚低涡的控制，地面受冷锋影响；河谷上游中亚地区存在700 hPa风向辐合、850 hPa风向切变，动力及水汽辐合机制配合较好，并配合有中尺度的对流系统；降水时段，河谷大部比湿在8~9 g·kg⁻¹，西部局地到达10 g·kg⁻¹，东部、南部山区在10~11 g·kg⁻¹，东部局地达到12 g·kg⁻¹；散度场、垂直速度场的配置，产生了此次暴雨过程所必须的辐合上升运动，同时有较强的不稳定条件，为对流行性降水提供了不稳定能量；雷达回波显示，大降水天气主要属于层状云降水过程，雷达回波成片状、回波强度偏弱；傍晚至夜间，山区局地出现对流云降水，回波成块状，回波强度大于45 dBz。

Abstract: This paper analyzes a regional rainstorm weather process in the Ili River Valley from the daytime to the night of August 18, 2024, using conventional observational data and radar data. The results show that when the rainstorm occurs, 500 hPa in the Ili River Valley is controlled by the West Siberian low vortex, and the ground is affected by the cold front. In the Central Asia region of the upper reaches of the river valley, there exists 700 hPa wind direction convergence and 850 hPa wind direction shear. The dynamic and water vapor convergence mechanisms are well coordinated, and there is also a mesoscale convective system. During the precipitation period, the specific humidity in most of the river valleys was 8~9 g·kg⁻¹, locally reaching 10 g·kg⁻¹ in the west. In the mountainous areas of the east and south, it was 10~11 g·kg⁻¹, and locally reaching 12 g·kg⁻¹ in the east. The configuration of the divergence field and the vertical velocity field generated the convergent upward movement necessary for this rainstorm process, and at the same time, there were strong unstable conditions, providing unstable energy for the epidemic precipitation. Radar echoes show that the heavy precipitation weather mainly belongs to the layered cloud precipitation process, and the radar echoes are sheet-like with relatively weak echo intensity. From the evening to the night, convective cloud precipitation occurred in some areas of the mountainous region. The echoes were blocky and the echo intensity was greater than 45 dBz.