An extremely heavy rainstorm occurred on 14-15 July 2022 in Longdong, Gansu Province, which is located in semi-arid region, the daily rainfall and hourly rainfall intensity at several stations broke the historical extreme values. Based on the minutely and hourly precipitation observation data from 20:00 BST 14 to 20:00 BST 15 July 2022, the daily and hourly precipitation data from 192 regional meteorological stations since the establishment of them in Qingyang of Gansu Province, and the CMPAS (CMA Multi-source Merged Precipitation Analysis System) 10-minute and hourly precipitation data, the precipitation characteristics and extremity of the torrential rain event are analyzed. The results show that the extremely torrential rain event is characterized by large cumulative precipitation, concentrated rainfall area of rainstorm and above, strong convective precipitation, stable and less movement of the rainfall centers, and long duration of short-term strong precipitation, among which the extremities of cumulative precipitation, hourly precipitation intensity and short-term heavy precipitation duration are obvious. The heavy rainstorm center, Zhaijiahe station, is located in the middle and north part of Qingcheng County, the maximum accumulated rainfall is 373.2 mm, which is the maximum since the station establishment, and is nearly twice of daily precipitation extreme values at all national stations in Gansu Province. The maximum hourly rainfall is 84.9 mm, ranking the third in historical records at all stations in Qingyang, and the longest duration of short-term strong rainfall is as long as 6 hours, which is the maximum in historical records at all stations in Qingyang since establishment of them. The evolution of minutely precipitation shows that the precipitation intensity in the heavy precipitation center has pulsating change, and the precipitation location has swing in the east, west, south and north, but the swing amplitude is small.

Abstract: The two regional shorttime heavy precipitation processes occurred in southeastern Gansu on April 19-20, 2019 (hereinafter using abbreviation “4·19”) and on April 26-27, 2019 (hereinafter using abbreviation “4·26”). Based on the conventional meteorological observations and ERA5 reanalysis data, the dynamic characteristics of two processes were analyzed through the diagnosis of physical quantities including frontogenesis function, temperature advection and vertical wind shear. The results are as follows: (1) The two processes belonged to baroclinicfrontogenesis severe convection, in which cold advection existed in the upper air, cold and warm air converged in low level, and obvious cold fronts and cold shear lines existed on the ground. (2) Under the same significant baroclinic atmospheric conditions, the dynamic characteristics of the two processes were significantly different. “4·19” process presented the characteristics of frontal precipitation, in which the cold air was relatively deep, strong and cold advection in the middle and low layers drove the lowlevel frontogenesis, and convection occurred under the dynamic unstable conditions forced by uplift of the front. However, “4·26” process had obvious characteristics of convective precipitation, in which cold air was diffused in the lower and near ground layers, and convective activity occurred under the combined action of near ground layer frontogenesis and lowlevel jets, and it was dominated by thermal instability. (3) The frontogenesis functions on 700 hPa and 850 hPa could quantitatively describe the temporal and spatial distribution and evolution characteristics of affecting systems in the lowlevel and near ground layer. Since the near ground layer trigger system was difficult to define due to the influence of terrain, especially in “4·19” process the pathes of cold air in the lower layer and near ground layer were complicated, the frontogenesis function could be used as a physical quantity index for the near ground layer trigger system.