Comprehensive analysis of the extreme short-time heavy rain event on 26 June 2022 in Jinsi Gorge, Shangluo

Abstract

Affected by the Hetao trough and low vortex, an extreme short-term heavy rainfall (referred to as the "6.26" event) occurred on 26 June 2022 from 12∶00 BT to 13∶00 BT in the western part of Shangnan County in Shaanxi province. During this process, an hourly rainfall of up to 108.3 mm was observed. This event was a typical local heavy rainstorm event caused by a newly-born mesoscale thunderstorm, which was characterized by its localized, sudden, short duration, and high-intensity precipitation. All numerical models failed to predict this event. Based on the data from conventional meteorological observations, encrypted automatic weather stations, Doppler weather radar, and the fifth-generation atmospheric reanalysis data of the European Center for Medium-Range Weather Forecasting (ERA5), this study analyzed in detail the environmental field characteristics and convective triggering mechanisms of this short-time heavy precipitation event. The results are as follows: (1) This event occurred under a combined circulation background of the 500 hPa low trough in Hetao and 700 hPa low vortex shear slowly moving eastward. The dynamic uplift and energy conditions over Shangnan were favorable, and the K-index reached 42.83 ℃ before the convection occurred. (2) The local abundant water vapor and the strong vertical upward movement at the lower level could rapidly transport the water vapor upward, which was conducive to the formation of short-term heavy rain over Jinsi Gorge. (3) The small and medium-scale surface convergence line formed between the local circulation caused by the thermal heterogeneity underlying surface near Jinsi Gorge and the local flow field caused by variable pressure wind is the main reason for the extremely short-term heavy precipitation in Jinsi Gorge.In this process, the special valley terrain of Jinsi Gorge played a significant role. On the one hand, it triggered the generation of convection. On the other hand, because of its block, the low-level southeast airflow rose along the mountain slope. This further strengthened the convergence of the atmosphere over Jinsi Gorge, which finally enhanced the precipitation of this rainstorm.

Keywords

• local heavy rain
• newly-born thunderstorm
• mesoscale convergence line
• topographical action