Abstract:

In order to explore the triggering mechanism of convective rainstorms in the northwest plateau of Yunnan, this paper used multi-source detection data to diagnose a typical convective rainstorm process in Lijiang on June 24, 2024. The results show that: (1) This process was primarily influenced by the convergence zone between the subtropical high pressure and the Yunnan-Burma high pressure at 500 hPa, in conjunction with a shear line at 700 hPa, and combined with cold air moving southward, it formed an unstable atmospheric structure, providing sufficient dynamic condition and a favorable circulation pattern for heavy precipitation. (2) This heavy rainfall was caused by the β- and γ-mesoscale convective cells generated locally, corresponding to a maximum radar reflectivity of 59.5 dBZ, and there was velocity blurring on the velocity map, along with features such as vortices and weak mesocyclones. (3) The moisture of the heavy rainfall originated from the Bay of Bengal and the South China Sea. Under the influence of topographic convergence and lifting, a zone of strong moisture convergence existed from the central to the southeastern part of Lijiang, which corresponded well with the position of the shear line. The southwesterly jet stream transported warm and moist air and intensified low-level convergence, and the upper-level northwesterly jet stream strengthened upward motion through a suction effect. The intrusion of cold air further promoted the maintenance of convection. The strong water vapor accumulation combined with the dynamic uplift conditions of lower-level convergence and upper-level divergence was the main cause of the local heavy rainstorm. (4) The combined effect of the north-south trending mountain in Lijiang and the surface convergence line triggered and intensified convection through topographic lifting and airflow convergence, becoming an important factor in continuous triggering and maintenance of convection during this heavy rainfall event. An easterly airflow served as a reliable indicator for the occurrence of severe convection. (5) In the precipitation echoes of cumulus clouds, the negative flash peak occurred approximately 40 minutes ahead of the heavy precipitation, while in the precipitation echoes of stratiform mixed clouds, there was a phenomenon of a precipitation peak occurring earlier.

Key words: the northwest plateau of Yunnan, convective heavy rainstorm, multi-source data

摘要：

为探究滇西北高原对流性暴雨的触发机制，利用多源探测资料对2024年6月24日云南丽江市一次典型对流性暴雨过程进行诊断。结果表明：（1）此次过程主要受500 hPa副热带高压和滇缅高压之间的辐合区与700 hPa切变线共同影响，配合冷空气南下形成不稳定层结，为强降水提供了充足的动力条件和有利的环流背景。（2）大暴雨天气过程由局地生成的β中尺度、γ中尺度对流单体产生，对应雷达反射率因子最大达59.5 dBZ，速度图上存在速度模糊、涡旋、弱中气旋等特征。（3）暴雨水汽来源于孟加拉湾和南海，在地形辐合抬升作用下，丽江中部至东南部存在强水汽辐合区，强水汽辐合区与切变线位置对应良好；西南急流输送暖湿气流并增强低层辐合，高层西北急流通过抽吸作用加强上升运动，冷空气入侵进一步促进对流维持，强水汽聚集配合低层辐合、高层辐散的动力抬升条件，是局地大暴雨发生的主要原因。（4）丽江市南北走向山脉与地面辐合线共同作用，通过地形抬升和气流辐合触发并加强对流，成为此次大暴雨过程中对流持续触发和维持的重要因素，偏东气流对强对流发生具有较好的指示意义。（5）积状云降水回波中负闪峰值超前强降水约40 min，而积层混合云降水回波中则出现降水峰值提前现象。

关键词: 滇西北高原, 对流性大暴雨, 多源资料