Anylysis of A Regional Torrential Rain in East of Qinling-Bashan Mountainous Area

Based on data of conventional observation,NCEP reanalysis,and infrared satellite images,a regional torrential rain event occurred in Ankang and Shangluo between 10th and 11th of July in 2009 was analyzed through synoptic analysis and dynamic diagnosis method.The results showed that the event occurred under a circulation pattern of two troughs with a ridge.A trough moved eastwards from the Tibet plateau,while the subtropical anticyclone maintained over Yangtze River,accompanied with active low-vortex motions on lower levels and favorable dynamic and thermal condition,which were the pivotal causation of this torrential rain event.On lower levels,wind shear formed a 人shape which contributed to accumulation of water vapor in rain site.The water influx was good at quantity on 700 hPa level but showed weak accumulation.On 850 hPa level over the rain site,the water vapor converged fiercely,which covered the weak water transfer.Although there was a weak convergence on upper levels,the strong convergence on 850hPa level was favorable for the water vapor transferring to upper levels.The K index maintained above 36 ℃ according with the rain site.The appearance of peak value of K index was earlier than that of the torrential rain,which was correlated to the emergence of the high energy axis of 80 ℃.Meanwhile,the infrared cloud images indicated the consecutive genesis and disappearance of convective cells among frontal cloud system with favorable water vapor and dynamic conditions contributed to the occurrence of the torrential rain.