重庆市綦江地区短时强降水天气分析

Analysis of short-term heavy rainfall weather in Qijiang of Chongqing

利用綦江近年的观测资料、Micaps、地闪资料,分析綦江短时强降水发生的时空分布规律及其发生前的物理量(K指数、SI指数、CAPE指数等)预报(预警)指标。结果表明,綦江各街镇每年均有不同频次的短时强降水发生,多年累计频次呈西北向东南逐渐增多的趋势,与綦江西南高、东北低的地貌特点较为一致。短时强降水都发生在春、夏、秋季,且多发生在14时-次日08时之间。綦江短时强降水主要有深厚湿层型、上干下湿型两种,且发生前往往会有K指数大值区、SI指数负值大值区、θse大值区、低层涡度大值区以及水汽通量散度负值大值区,只要SI指数呈负值、K指数>30、经过修正后的CAPE值>700这三项中有两项满足时,且中低层垂直风切变较小时,对短时强降水的发生具有较好的指示意义。当SI指数的负值绝对值越大、K指数越大、CAPE值越大,发生强对流天气的概率越大。

Based on the observation data,MICAPS and ground flash data in recent years,the temporal and spatial distribution of the short-term heavy precipitation in Qijiang River and the prediction(early warning)indexes of its physical quantities(K index,Si index,Cape index,etc.)before its occurrence were analyzed.The results show that the short-term heavy precipitation occurs in different frequency in each town of Qijiang River every year,and the accumulated frequency increases gradually from northwest to Southeast in many years,which is consistent with the geomorphological characteristics of the southwest and northeast of Qijiang River.Short-term heavy rainfall occurs in spring,summer and autumn,and mostly occurs between 14∶00 and 08∶00 the next day.There are two main types of short-term heavy precipitation in Qijiang River,i.e.deep wet layer type and upper dry and lower wet layer type.In the past,there will be large K-index area,large negative SI-index area,large se-value area,large low-level vorticity area and large negative water vapor flux divergence area.As long as the SI index is negative,K-index is greater than 30,and the revised CAPE value is greater than 700,two of them will meet,and the middle and lower layers will be satisfied.When the vertical wind shear is small,it has a good indication for the occurrence of short-term heavy precipitation.The greater the negative absolute value of SI index,K index and CAPE value,the greater the probability of severe convective weather.