Analysis of water vapor during short-time heavy rainfall events at the edge of subtropical high in Liaoning Province

Abstract

The short-time severe rainfall at the edge of the western Pacific subtropical high (referred to as the Subtropical High) is characterized by strong bursts, concentrated precipitation, and low predictability, often posing challenges for forecasting. Eight regional short-time severe rainfall events at the edge of subtropical high in Liaoning from May to October during 2021 and 2022 were examined. The synoptic situations of these events are divided into two categories according to the synoptic systems that cooperate with the subtropical high, which are the low trough at the edge of the subtropical high and the vortex at the edge of the subtropical high. Based on the European Center for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data, NCAR/NCEP GDAS data, conventional observation data, and HYSPLT4 model, the variation characteristics of the water vapor transport of the short-time heavy rainfall events during these two categories are studied. The changes in water vapor flux and the role of low-level jets were analyzed by investigating typical rainfall cases with the largest coverage of heavy precipitation and the most number of short-term heavy precipitation stations. The results are as follows. Under the upper-level trough and the cold vortex at the edge of the subtropical high, the water vapor over Liaoning mainly comes from the Central Eurasian continent, the eastern coast of China, the Inner Mongolian area, and North China. Despite the influence of similar synoptic systems, the water vapor transport pathways are significantly different, corresponding to differences in air mass sources, movement trajectories, and the way air mass obtains water vapor. The evolution of the high-value area of water vapor flux is consistent with the variation of the wind field at 850 hPa. During short-time heavy rainfall events, under the situation of low-level jet uplift and water vapor transport, the positions of the high-value area of water vapor convergence, strong updraft area, and water vapor transport pathways are closely related to the position of the low-level jet. The air mass from the Central Eurasian continent and the Inner Mongolian area contribute to 32% of the water vapor supply during the short-time severe rainfall events at the edge of the subtropical high in Liaoning.

Keywords

• short-time severe rainfall
• water vapor transport
• hysplit
• liaoning province