一次短时强降水过程中的干侵入作用

Analysis of Dry Intrusion Impacts on a Short-time Heavy Rainfall Process

以2012年7月15日凌晨榆林地区一次短时强降水过程为研究对象,利用NCEP 1°×1°再分析资料、FY-2E卫星资料及常规气象观测资料,通过卫星水汽图像和大气动力场相结合的方法揭示冷涡影响下降水过程中干侵入的特征及其对短时强降水发生、发展的作用机制。结果表明:此次短时强降水过程中干侵入特征明显,卫星水汽图像上的黑体亮温高值区与干冷区相对应,干冷区的伸入使得对流云团边缘亮温梯度增大,同时对流云团发展;干侵入与对流层高层的下沉运动、高值位涡以及干冷区相对应,因干冷空气叠加在暖湿气流之上,在强降水区上空出现了对流不稳定层结,为短时强降水的发生创造了有利的环境条件。另外,此次降水过程水汽条件主要集中在对流层低层,风场辐合带来的短时间水汽辐合为短时强降水集聚了一定的水汽条件。在地面中尺度辐合线的触发作用下,将不稳定层结中包含水汽的气块抬升,从而形成降水。

The NCEP 1°× 1°reanalysis data,FY-2E satellite images,conventional meteorological data,and the method of combining satellite cloud images with atmospheric dynamic field were used to analyze the dry intrusion characteristics under the influence of cold eddy and the role of the dry intrusion during the short-time strong rainfall which occurred in Yulin of Shaanxi Province on July 15, 2012. The results show that the characteristics of the dry intrusion was significant during the short-time strong rainfall process,the high value area of TBB on satellite water vapor images corresponded to the dry cold area of upper troposphere,while the stretching of the cold dry area made the TBB gradient on convective cloud edge increase,at the same time convective cloud developed. The dry in-trusion corresponded to the sinking motion,high value area of potential vorticity and dry cold areas in the upper troposphere,the insta-bility stratification appeared over the heavy rainfall region due to the dry cold air overlaying the warm wet air,which created favorable environmental conditions for the occurrence of the short-term heavy rainfall. In addition,water vapor of the rainfall process mainly concentrated in the lower troposphere,short-term moisture convergence caused by wind convergence created a favorable moisture con-dition for the short-term heavy rainfall. The lifting of air mass that contained water vapor caused by the trigger mechanism of mesoscale convergence line on the ground led to precipitation.