摘要
利用FY-2卫星资料、NCEP再分析资料和常规观测资料,分析研究了2016年5月6日四川盆地暴雨对流云团的特征及其形成机制。结果表明:四川盆地对流云团易发生在青藏高原东侧边坡陡峭地形带,初生对流云团的云顶亮温低于-45℃,边缘最大温度梯度为15~20℃,水汽-红外通道亮温差值介于-5~0℃,分裂窗-红外亮温差值介于0~2℃。强降水出现在红外和水汽亮温快速下降到最低值、水汽-红外通道差值达0℃附近、分裂窗-红外亮温差为正值和温度梯度达0℃后的几小时内,最大雨强出现在强对流云团成熟后开始迅速减弱的初始阶段(即云顶亮温开始回升的阶段)。较大范围的强降水由发展成熟的云顶最低亮温约为-70℃的对流云团产生,主要出现在红外亮温低于-50℃的区域,集中在红外亮温-65℃^-60℃、水汽亮温为-65℃^-60℃的云顶较为平滑的次低值中心区域内,并不与云顶最低亮温中心相吻合。机制分析表明,对流云团生成区域均受偏东风影响,且形成于高的对流不稳定能量条件下,发展于高湿区,近地层冷空气扩散南下与气旋式流场中的辐合共同触发对流在辐合线以北生成,而中层垂直风切变的加强、中低层暖平流和高层冷平流的发展促使对流云团发展旺盛。
In this study, the characteristic and formation mechanism of convective cluster over Sichuan Basin on 6 May 2016 are analyzed with FY-2 satellite data, NCEP reanalysis data and conventional data. The results indicate that the convective clusters tend to form at the buffer zone of the western Sichuan Plateau, with their cloud top brightness temperature less than -45℃ and maximum temperature gradient greater than 15℃. Meanwhile, the difference between the cloud top brightness temperature measurements from IR3 and IR1 can range from -5 ℃ to 0 ℃ and the difference of those from IR2-IR1 is between 0 ℃ and 2 ℃. Heavy rain occurs in a few hours after the cloud top temperature quickly drops to the lowest temperature, the difference between the cloud top temperature measurements from IR3 and IR1 is near 0℃, and the difference of IR2-IR1 is positive and the temperature gradient of 0 ℃. Furthermore, the heavy rain starts at the time when the brightness temperature starts to rise again. Typically, wide range of heavy rain is mainly produced by the severe convective clusters whose cloud top brightness temperature is less than -70℃ and it tends to happen within the lower and smooth regions with the cloud top temperature between -65℃ and -60℃ and the IR3 brightness temperature from -65℃ to -60℃. Moreover, it is not in con- formity with the lowest temperature center of cloud top. Mechanism analysis shows that the clusters＇ ambient characteristics include high instable convective energy, sufficient moisture and east wind flow. The cold airflow in boundary layer and convergence line on surface are the main mechanism of the convective cluster trigger. The enhancement of the vertical wind shear, and the development of the middle level warm airflow and the high level cold airflow jointly prompt the intensification of the severe convective clusters.
出处
《气象》
CSCD
北大核心
2017年第12期1487-1495,共9页
Meteorological Monthly
基金
国家自然科学基金项目(41275052
41375091和41405071)
四川省气象局课题(川气课题2015-青年-11)共同资助
关键词
对流云团
发展条件
对流触发
地面辐合线
convective cluster, development condition, convection trigger, surface convergence line
