双流机场“7.21”暴雨微物理特征及触发维持机制分析

利用天气雷达、地面自动站和微波辐射仪等多种气象探测资料,对2017年7月发生在成都双流机场的一次暴雨过程进行了分析。结果表明:此次暴雨发生在弱天气系统强迫条件下,大气层结呈现弱对流抑制、低抬升凝结高度、中等对流有效位能,湿层深厚,低层较暖且低层无急流影响。短时强降水由中尺度系统直接产生,午夜前的初始对流由高压西北部偏南暖湿气流与山体下滑冷气流相互作用,结合山前强水平温度梯度产生,之后在冷池和边界层暖湿气流作用下生成新的对流。产生强降水的回波结构密实,暖云特征突出,属于热带低质心降水系统。对抬升凝结高度、自由对流高度、湿层厚度等的分析表明,水汽条件较为极端,但由于系统整体属于前向传播,无明显的"列车效应",限制了实际降水效率。

Microphysical characteristics,initiation and maintenance of heavy rainfall at Chengdu Shuangliu Airport on 21 July 2017

A heavy rainfall occurred at Chengdu Shuangliu Airport on 21 July 2017 was studied based on dataset from ground-based Doppler radar, automatic weather stations and microwave radiometer, et al. The results show that the ambient conditions and dynamic forcing prior to the event were weak and characterized by small value of Convective Inhibition(CIN), moderate Convective Available Potential Energy(CAPE),low Lifting Condensation Level(LCL),deep warm layer and moist southerly flow. The initial convection storms were triggered mainly by a convergence line formed by the warm flow from the cities and cold down-lope wind in front of mountains, which combined with the intense temperature gradient. And then the outflow of the cold pools located southerly impacting with the warm,moist boundary layer introduced the other convective storms. The micro-physical analysis indicates that the heavy rainfall was mainly composed of high-precipitation-efficiency warm rain process supported with low-centroid cumulonimbus structures. It also suggested that the forward-propagation storms have played a big role in the local heavy rainfall with intensifying southerly flow and dramatic water vapor supply.