Analysis of impact of eastward-moving southwest vortices on regional heavy rainfall in Yangtze River Delta

Abstract

[Objective] The eastward-moving southwest vortex is an important weather system affecting drought and flood variations in the Yangtze River Delta region of China. However, its specific impact on the Yangtze River Delta region remains incompletely understood. The aim is to investigate the detailed characteristics of regional heavy rainfall in the Yangtze River Delta influenced by eastward-moving southwest vortex. [Methods] Using the “Southwest Vortex Almanac”, CN05. 1 gridded precipitation data, and ERA5 reanalysis data, statistical analysis and case comparisons were conducted on the movement characteristics of southwest vortices and the characteristics of regional heavy rainfall in the Yangtze River Delta region caused by eastward-moving southwest vortices. [Results] The result showed that from 2012 to 2019, a total of 716 southwest vortices were generated. The primary movement path of southwest vortices exiting their source region was eastward. Eastward-moving southwest vortices accounted for approximately 30% of the total cases generated, contributing more than 10% of the total precipitation in the Yangtze River Delta region. [Conclusion] The findings indicate that the eastward movement and development of southwest vortices are favored when the East Asian Trough and the Northwestern Pacific Subtropical High are relatively strong. The impact of eastward-moving southwest vortices on precipitation in the Yangtze River Delta region exhibits significant spatial heterogeneity, with the maximum contribution mainly located in the western part of the region. The areas of heavy precipitation are generally consistent with the movement paths of the southwest vortices, the intensity of the southwesterly warm and moist airflow on the southern side of the vortices, and the locations of strong upper-and lower-level convergence and divergence zones. The specific characteristics of heavy rainfall in the Yangtze River Delta region influenced by eastward-moving southwest vortices, including the large-scale circulation patterns and meso-and micro-scale dynamic configurations, demonstrate their unique impact on heavy rainfall events in this region. These findings provide theoretical references for the operational forecasting of heavy rainfall in the Yangtze River Delta region potentially caused by eastward-moving southwest vortices.

Keywords

southwest vortex / eastward-moving / heavy rainfall / statistical analysis / Yangtze River Delta region / circulation pattern / dynamic analysis / moisture diagnostic