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.

Characteristics of Atmospheric Rivers over the East Asia in Middle Summers from 2001 to 2016

Atmospheric Rivers(ARs) are narrow and elongated water vapor belts in troposphere with meridional transport across the mid-latitudes towards high-latitudes. Compared with ARs occurred over the northeastern Pacific, the western coast of North America and Europe, the ARs over the East Asia have received less attention. In this paper, the characteristics of ARs which affected China in the area 20?–60?N, 95?–165?E in the middle summer season from 2001 to 2016 were investigated by using European Center for Medium-Range Weather Forecasts(ECMWF) ERA-Interim reanalysis data and Multi-functional Transport Satellites-1 R(MTSAT-1 R) infrared data. Totally, 134 ARs occurred during that period, and averagely 8.4 ARs occurred per year. Statistically, 101 ARs were in east-west orientation, and 33 ARs were in north-south orientation, which accounts for about 75% and 25%, respectively. Herein we report the occurrence number, duration time, intensity, length, width, ratio of length to width, and extension orientation of these ARs, which provide the basic information for those who have interest in ARs over the East Asia.

Contribution of Atmospheric Rivers to Precipitation and Precipitation Extremes in East Asia:Diagnosis with Moisture Flux Convergence

Atmospheric rivers(ARs),the long and narrow conveyors of intense moisture transport,have a non-negligible impact on hydrometeorological events over the extratropical regions.This study analyzes the climatology and interannual variability of ARs and their quantitative association with precipitation and precipitation extremes over East Asia(EA)during 1979-2019,based on calculations of not only moisture transport but also moisture flux convergence.It is found that the ARs over EA occur frequently in spring and summer,accounting for 25%-40%of seasonal precipitation and 60%-75%of extreme precipitation over EA.Increases in AR frequency are observed over EA during post-El Ni?o summers,meanwhile the AR-related anomalous moisture convergence is found leading to the increase of extreme precipitation.Specifically,increased ARs account for 70%-90%of total precipitation anomalies and up to 90%of extreme precipitation anomalies over the middle-lower reaches of the Yangtze River,and the anomalies of moisture flux convergence are caused mainly by changes in horizontal wind convergence rather than moisture advection during the post-El Ni?o summers.