2008年江苏持续性降雪中的水汽和动力抬升机制分析

2008年1月下旬江苏省出现了历史罕见的持续性暴雪过程,研究发现,降雪量的大小与低空急流的日变化相对应,暴雪过程中700 hPa西南急流对水汽的输送起着重要的作用,作为大尺度天气系统,700 hPa急流的加速发生在降雪量增大之前,其值阈大小与6 h降雪量之间没有对应关系,急流减弱在暴雪结束以后;降雪的发生和发展与南北风的增大和冷暖平流有关,低层偏北风作为冷垫对暖湿气流的抬升和水汽的凝结起到了一定的作用;江苏降雪过程中水汽主要来源于700～500 hPa,低层东风气流对黄海南部的水汽输送非常有限;强降雪的发生与700 hPa水汽通量散度相对应,水汽通量散度辐合增大,降雪量增大;在降雪过程中垂直运动对降雪量的大小有很好的指示意义。

The Water Vapor and Dynamic Lifting Mechanism of Continuous Snowfall in 2008 in Jiangsu

In late January 2008,there were rare durative snowstorm in Jiangsu Province.The study shows that the size of snowfall corresponds to the diurnal variation of low-level jet.During the snow storm,the southwest jet at 700 hPa played an important role in the transport of water vapor.As large-scale weather systems,the acceleration of the jet at 700 hPa occurs before snowfall’s increase,its range did not correspond to the 6 hours accumulated snowfall,and it weakened after the end of snowstorm.The occurrence and development of snowstorm have a relationship with the increase of north-south wind and the temperature advection,the low-level north wind as cold pad had played a certain role for the advection of warm and humid air and the condensation of water vapor.The water vapor mainly comes from 700 hPa to 500 hPa,the low-level easterly flow had a limited role for the transportation of water vapor on the southern Yellow Sea.The occurrence of snowstorm corresponds to the divergence of water vapor flux at 700 hPa.Snowfall increased with the increase of moisture flux divergence.During the snowstorm,vertical movement has good indication to the snowfall.