陕西4次台风远距离暴雨过程的水汽条件对比

利用NCEP再分析资料和常规观测资料,对比分析了陕西省4次台风远距离暴雨过程期间的水汽输送、水汽收支和水汽含量特征。结果表明：远距离台风用直接和间接2种方式影响热带低纬地区水汽向陕西方向的输送,中高纬度地区西风槽与高压系统直接参与暴雨区附近水汽的输送与再分配过程。远距离台风出现时,暴雨区南边界始终存在水汽的输入,占净输入的68%,西边界多为水汽的输出方,东边界上水汽收支变化趋势与台风移动路径密切相关。川东地区西南涡维持、发展并向东北向移动时,陕西水汽总收支成倍增大。台风远距离暴雨出现前12 h左右,暴雨中心低层比湿出现极大值,对应的风场辐合中心一般出现在比湿增加之后。

Moisture Comparative Analysis on Typhoon Remote Rainstorm Prosesses in the Eastern Region of Northwest China

Characteristics of moisture conditions during four typhoon remote rainstorm processes that occurred in Shaanxi Province were analyzed and compared based on NCEP reanalysis data and the conventional observation data.Results show that there were two ways by which typhoons influenced remote transportation of tropical moisture to Shaanxi Province,while trough and high pressure system in the westerlies were directly involved in moisture transport and redistribution nearby rainstorm areas.During remote typhoon activity,moisture input was always in the south boundary of Shaanxi,which accounted for 68% of a net input.Meanwhile,moisture output mainly occurred in the the western boundary,and vapor budget tendency in east boundary was closely related to typhoon path.The total water vapor budget over Shaanxi would be double when the southwest vortex developed over the east of Sichuan and moved to northeast.About12 hours before heavy rain,the maximum of the specific humidity would occurred in lower level over heavy rainstorm centers,while the wind convergence centers generally appeared after the specific humidity increase.