Analysis on the characteristics of extreme precipitation induced by Typhoon Haikui (2023) residual vortex in Guangzhou

Subject to the impact of Typhoon Haikui residual vortex, Guangzhou suffered the third strongest rainstorm in nearly 10 years from 7 to 8 September 2023, which has the characteristics of large total amount, wide coverage range, extreme rainfall intensity, long duration and obvious nocturnal precipitation. Based on multi-source data, the precipitation conditions, large-scale circulation causes of extreme precipitation and mesoscale characteristics of nocturnal precipitation are analyzed. The results are as follows. (1) The retention of Haikui residual vortex, the convergence and maintenance of strong monsoon and southeast jet which provided abundant water vapor, and the divergence caused by South Asia High, which constitutes the favorable large-scale circulation background for the extreme precipitation. (2) The occurrence of extreme precipitation is closely related to the anomaly of large-scale circulation and physical parameters. 200 hPa divergence, 925 hPa convergence and 925 hPa water vapor flux convergence all have significant extremes, generally deviating from the standard deviation of climatic state by four times. There exists a moderate-intensity positive anomaly center of pseudo-equivalent potential temperature in Guangzhou. The abnormal extreme dynamic, water vapor and thermal conditions lead to the occurrence of extreme precipitation. (3) The strengthening of southeast jet, the triggering of the mesoscale energy front, the enhancement of water vapor convergence and warm advection are important incentives for the night rain. It is generated by the backward propagation of convective cells formed train effect and long duration of mixed cloud precipitation, with significant low echo centroids and warm cloud precipitation characteristics. The high concentration of medium and small raindrops is the main cloud microphysical feature.