Atmospheric Rivers and Mei-yu Rainfall in China: A Case Study of Summer 2020

Atmospheric rivers (ARs) are long, narrow, and transient filaments of strong horizontal water vapor transport that can lead to extreme precipitation. To investigate the relationship between ARs and mei-yu rainfall in China, the mei-yu season of 2020 in the Yangtze-Huaihe River basin is taken as an example. An adjusted AR-detection algorithm is applied on integrated water vapor transport (IVT) of the ERA5 reanalysis. The JRA-55 reanalysis and the data from Integrated Multi-satellite Retrievals for GPM (IMERG) are also utilized to study the impacts of ARs on mei-yu rainfall in 2020. The results reveal that ARs in East Asia have an average length of 5400 km, a width of 600 km, a length/width ratio of 9.3, and a northeastward orientation of 30°. ARs are modulated by the western North Pacific subtropical high. The IVT core is located at the south side of low pressure systems, moving eastward with a speed of 10° d −1 . For the cross sections of ARs in the Yangtze-Huaihe River basin, 75% of the total flux is concentrated below 4 km with low-level jets near AR cores. Moreover, ARs occur mainly in the mei-yu period with a frequency of 20%–60%. The intensity of AR-related precipitation is 6–12 times that of AR-unrelated precipitation, and AR-related precipitation contributes about 50%–80% to total mei-yu precipitation. As shown in this case study of summer 2020, ARs are an essential part of the mei-yu system and have great impacts on mei-yu rainfall. Thus, ARs should receive more attention in research and weather forecast practices.