关键词: 大气科学;极端降水;气候特征;环流分型;合成分析;

Abstract: To improve the forecasting accuracy of extreme precipitation events in Hanjiang River Basin during the mid-summer, based on its daily precipitation data from 1970 to 2020,the extreme precipitation events in mid-summer in Hanjiang River Basin were defined by 95% fractional method, including climate characteristics, atmospheric circulation and sea surface temperature background.The atmospheric circulation of regional extreme precipitation events were divided into five main types by L-J method.The results show that:(1) The extreme precipitation in the mid-summer of the Hanjiang River basin has significant inter-annual variation characteristics, and the distribution of the extreme precipitation threshold is similar to the climate state over the region, which is “large at the edge, small in the middle”,and the extreme center is at Zhenba Town in the southwest of the basin.(2) The typical circulation field of extreme precipitation is Baikal trough, Ural Mountanins high, Okhotsk blocking high and the strong West Pacific subtropical high.The water vapor replenishment from the sea combined with upward movement throughout the entire layer provides the conditions for extreme precipitation.In addition, the superposition of the external forcing of the SST anomalies in the two key areas(the Eastern Central Pacific and the western Pacific warm pool)result in the stable maintenance and enhanced intensity of the atmospheric circulation.(3) The regional extreme precipitation are dominated by S type, SE type, C type, CSW type and CS type.By comparing the circulation of regional extreme precipitation events in the Hanjiang River Basin on August 22 and 29 in 2021,it was found that the circulation conforms to the C type on 500hPa and the CS type on 850hPa, the CS type on 500hPa and the S type on 850hPa, which can be offered as an subjective approach to classification and prediction of extreme precipitation events in mid-summer in Hanjiang River Basin in the future.

Key words: atmospheric science; extreme precipitation; climatic characteristics; circulation classification; synthetic analysis;