Analysis of the Causes for a Torrential Rain in Guangzhou and Dongguan on May 22,2020
Using the NCEP FNL data,observations from surface automatic weather stations and data from a wind profiler,this work analyzed the causes for a torrential rain which took place in Guangzhou and Dongguan on May 22,2020.The results are shown as follows.The rain was mainly governed by such synop-tic systems as weak meso-β-scale waves propagating downward from a northwesterly flow at 500 hPa,an ultra low-level jet stream that enhanced nocturnally,and a low and a trough that developed as a result of weak in-filtrating cold air at the surface.While the jet stream provided extremely abundant amount of water vapor for the torrential rain,a highly unstable stratification and a thick layer of warm clouds were favorable for the effi-cient generation of intense warm-cloud rainfall.At the peak stage of the rainfall,a weak cool-pool outflow,formed from an intense mesoscale convective rain cluster,converged with a southwesterly jet stream,and the nocturnally enhancing southwesterly jet stream kept a warm tongue stably over the western part of Dongguan,leading to the formation of a flow converging zone with dense isotherms that affected the southeast of Guang-zhou and the west and north of Dongguan for about three hours.The cool-pool outflow descended to infiltrate into the lower portion of the warm southwesterly flow to cause the warm air to tilt and ascend,which was con-ducive to the repeated triggering of convection in the zone of dense isotherms and the generation of severe lo-cal rainfall.The southwesterly jet stream was comparable with a northwesterly steering flow in wind speed and confronted each other at an included angle ranging from 50°to 60°.It slowed down the moving speed of mesoscale convective cells and slowly increased the westerly component of the jet stream so that the convec-tion moved to the southwest gradually rather than in the direction of the steering flow.
synopticstorrential raincool poolconvection triggering and maintenanceDongguan
NETL
NSTL
万方数据
