Analysis of characteristics and causes of "8.12" extreme precipitation in Hubei Province

Extreme precipitation occurred in northern Hubei,with the maximum precipitation of 518.5 mm in 24 hours and 117.9 mm in 1 hour,causing serious disasters from 20:00 BT on August 11 to 20:00 BT on August 12,2021. Based on conventional meteorological observation data and ERA5 reanalysis data,the characteristics and synoptic causes of extreme precipitation for the event are preliminarily analyzed using statistical methods and synoptic diagnostic analysis methods. The results are shown below. (1) Although the characteristics of rain are different in different regions,the extreme rainstorm has the characteristics of large accumulated rainfall,strong short-term rainfall,concentrated precipitation period,strong disaster possibility,and extreme rainfall. (2) The rapid development,long duration and slow eastward movement of β-Mesoscale Convective System (M_βCS) are the main reasons for the extreme precipitation. (3) The main influence systems are the high level South Asia High (SAH),the upper jet,the middle level West Pacific Subtropical High (WPSH) and the low trough. The direct participants are the mid- low level wind shear,mesoscale vortex and easterly jet. (4) The abnormal strength and maintenance of 850-925 hPa mesoscale vortex and easterly jet lead to the formation of strong dynamic convergence center and strong water vapor convergence center in the lower layer,providing continuous vertical upward movement below 700 hPa. The jet also favors the strengthening of energy front and the establishment of high-energy region and low-level instability,which leads to the occurrence and development of convective heavy rain. (5) The precipitable water in the whole layer and the vorticity and the vertical velocity and specific humidity at 925-850 hPa show relatively abnormal extreme characteristics. In addition,its anomaly evolution trend is basically consistent with the evolution trend of rainfall intensity.