峡谷地形对两次极端降水的作用

利用地面加密自动站、常规观测资料、NCEP再分析资料和两种模式产品,对发生在宜昌峡谷地区2016年7月7日局地极端短时强降水过程和2018年4月22日稳定性极端降水过程形成原因及模式预报性能进行检验分析。结果表明:(1)强的块状回波稳定少动,造成7月7日高效率的对流降水。4月22日降水既有沿山中尺度对流回波造成的对流降水,也有螺旋状涡旋回波形成的锋面层状云降水。(2)山谷风形成中尺度切变线,触发对流,中尺度切变线发展为中尺度涡旋使对流加强是极端短时降水形成的主要原因。(3)地形强迫抬升使对流降水强度明显增大,锋面层状云回波受地形阻挡影响长时间维持是稳定性极端降水形成主要原因。(4)地形相差大的地区模式预报性能差异较大,模式对复杂地形下的对流降水预报偏弱,导致系统强度出现差异,进而影响降水强度预报。

Effect of valley terrain on two types of extreme precipitation

Based on observation data of automatic weather station, conventional observation data, NCEP reanalysis data and the forecast products of two models, the cause of formation and prediction of local extreme short-term heavy rainfall on 7 July 2016 and stability extreme rainfall on 22 April 2018 in Yichang Gorge were analyzed. Results show that:(1) the strong block echo is stable and less dynamic, which results in high efficiency convective precipitation on July 7. The convective precipitation increases obviously due to the forced uplift of topography, and the echo of front stratiform cloud is affected by terrain blocking, and the long-term maintenance is the main reason for the formation of stable extreme precipitation. (2) The main reason for the formation of extreme short-term heavy rainfall is that the valley wind forms mesoscale shear line, the mesoscale shear line stimulates convection, and the mesoscale shear line developes into mesoscale vortex to strengthen convection.(3) The intensity of convective precipitation increases obviously due to the forced uplift of topography, and the echo of frontal stratiform cloud is affected by terrain blocking and the long-term maintenance is the main reason for the formation of stable extreme precipitation. (4) The performance of regional models with large terrain difference is quite different, and the prediction of convective precipitation under complex terrain is weak, which leads to the difference of system intensity, and then affectes the prediction of precipitation intensity.