2018年8月深圳一次连续暴雨过程初步分析

利用NCEP FNL 1°×1°再分析资料、自动气象站数据和风廓线雷达等资料,对2018年8月28日至31日由季风低压造成的深圳连续暴雨过程进行了初步分析。结果表明:连续暴雨期间,南亚高压稳定少动,西北太平洋副热带高压呈双脊型并缓慢西伸,北脊阻挡西南季风北上,使得季风低压在双脊之间缓慢西移并发展加强,为持续暴雨发生提供了必要的大尺度环流条件。强盛时期的季风低压垂直伸展范围约8~9 km,直至对流层中层,与副高之间气压梯度加大,导致低空急流加强并向下传播,深厚的急流区为暴雨提供充足的水汽和能量。低空急流的向下传播时间早于短时强降水发生0.5~1 h。925 hPa及其以下的对流层底层风场呈气旋式辐合,是重要的抬升触发条件。而1 km以下风场由西南风转为偏南风,在地形抬升作用下加速上升运动,最大垂直上升速度达0.5 Pa/s,地形对降水具有显著的增幅作用。

A Preliminary Analysis of a Process of Persistent Heavy Rain in Shenzhen in August 2018

Using the NCEP FNL 1°×1°reanalysis and automatic weather stations and wind profilers data,this paper performs a preliminary analysis of a persistent heavy rain in Shenzhen caused by a monsoonal low from August 28 to 31,2018.The result is shown as follows.During the rain,a high over South Asia was stable and moved little,and a subtropical high in the western North Pacific had two ridges and extended to the west gradually.The northern ridge prevented a southwesterly monsoon from going northwards to cause the monsoonal low to move slowly to the west between the two ridges,develop and strengthen,supplying large-scale circulation conditions needed for the persistent heavy rain to happen.At the peak of its intensity,the monsoonal low extended vertically for 8~9 km all the way to the mid-stratosphere,and the pressure gradient became so large between the monsoonal low and the subtropical high that a low-level jet stream was strengthened and transported downwards,and the jet stream was deep enough to provide sufficient amount of water vapor and energy for the generation of the heavy rain.The downward transport of the low-level jet stream was 0.5~1 h earlier than the onset of short-range intense rain.At the level of 925 hPa and below,the wind field of lower troposphere converged cyclonically,making it an important condition for triggering uplifting motion.In the wind field below 1 km,the wind shifted from the southwest to the south,which accelerated upwards due to the uplifting effect at rates up to 0.5 Pa/s.The terrain enhanced the rain significantly.