Characteristics of the Atmospheric Rivers in Snowstorms Caused by Extratropical Cyclones in Northeastern China

Abstract

A statistical study on snowstorms in northeastern China caused by extratropical cyclones with and without the support of atmospheric rivers （ARs） was conducted using conventional observations， 6-hour and 24-hour precipitation data， as well as ERA5 reanalysis data from the European Center for Medium-Range Weather Forecasts from 2007 to 2020.In addition， the environmental fields in snowstorms with and without ARs support were compared.According to the findings， ARs occurred in 83 percent of snowstorms associated with extratropical cyclones， with 59% of ARs landing in northeastern China.ARs were most common in November and March， with nearly no ARs in December and January.On the one hand， the frequency and intensity of ARs were high during the snowstorms involving the southern and Huanghuai cyclones， and the associated precipitation was heavy.Snowstorms associated with Mongolia cyclones， on the other hand， had a low frequency of ARs and light precipitation.There were two branches of upper-level jets and strong low-level jets for the snowstorms with ARs.And a cold vortex was located at 500 hPa， forming the interaction between the cut-off low and the ARs， which was conducive to heavy rainfall.An obvious warm tongue and strong frontal zones were located at 850 hPa， which was favorable for water vapor transport and dynamic lifting with the support of ARs.And then it rained associated with the cold front and snowed associated with the warm front during snowstorms accompanied by ARs.Compared with snowstorms accompanied by ARs， there was one branch of upper-level jets and weak low-level jets for the snowstorms without ARs.And there was no cold vortex and a weak westerly trough at 500 hPa.The frontal zones and low vortex were weak at 850 hPa without the support of ARs.The upper-level divergence was weak and water vapor was poor， and it mostly snowed associated with the warm front in snowstorm events without ARs support.Water vapor during snowstorms with the support of ARs originated from the East China Sea， the Yellow and Bohai Seas， and the water vapor convergence in the boundary layer was wide and intense， and upward movement was strong with a thick low-level unstable layer.Water vapor during snowstorms without ARs support mainly originated from the Sea of Japan， where unstable stratification and upward movement were weak， and the boundary layer moisture convergence area was narrow and weak.ARs reflect not only strong water vapour transport but also better dynamic lifting.

Keywords

• extratropical cyclone
• snowstorm
• atmospheric river
• composite analysis