“20110730”辽宁大暴雨过程分析

Analysis of heavy rain on July 30,2011 in Liaoning province

利用常规气象资料、卫星云图、雷达回波、自动气象站资料和NCEP(1°×1°)再分析资料,对2011年7月30日辽宁短时大暴雨过程进行分析。结果表明:暴雨期间500 hPa高空槽与850 hPa切变线形成前倾形势,前倾槽为大暴雨的产生提供了有利的不稳定条件。暴雨过程中尺度分析表明,降水时空变率大;TBB等值线密集区和上冲云顶的位置对暴雨落区有较好的指示意义;强降水时,雷达回波强度达到65 dBz,且有逆风区和正负速度对出现,中小尺度强对流特征明显;地面等温线密集带与地面切变线(或中尺度低压)的共同作用触发了中尺度雨团,降水强度陡增。通过涡度方程诊断切变线形成动力机制得出,当正涡度变率发展加强时,切变线向正涡度变率大值区方向移动,产生辐合动力抬升条件;散度项对低层涡度变率的贡献最大,强辐合是低层切变线生成的动力机制之一。

Based on the conventionally meteorological observation data,satellite cloud images,Doppler weather radar echo data,the data from automatic weather stations and the NCEP/NCAR reanalyzed data （1 ° × 1 °）,a shorttime rainstorm process on July 30,2011 in Liaoning province was analyzed.The results show that upper trough at 500 hPa and shear line at 850 hPa form the forward-titling trough which provides favorable instability conditions for generation of rainstorm.The mesoscale analysis suggests that the temporal and spatial variation of precipitation is significant.The intensive contour zone of TBB and the location of the overshooting cloud of convective systems are indicative to the falling area of rainfall.The intensity of radar echo generally reaches 65 dBz during the strong rainfall and there exists the inversion wind area,and a couple of positive and negative winds.The mesoscale and microscale strong convective characteristics are significant.The dense area of isotherm and the surface shear line （or the mesoscale low pressure） trigger together mesoscale rain cluster,and the intensity of rainfall strengthens sharply.The dynamic mechanism of shear line formation is diagnosed by a vorticity equation,and it suggests that when the positive vorticity variability increases,shear line moves to its large value area and generates the dynamic convergence lifting conditions.Divergence contributes greatly to vorticity variability,and strong convergence is one of the dynamic mechanisms of shear line formation in low level.