Snow/Rainfall Anomaly in Winter of Northern China and Associated Atmospheric Circulation and Aerosol Distribution Features

Based on the NCEP/NCAR reanalysis data, China station precipitation data from 1960 to 2008, and aerosol optical depth (AOD) data in northern China from 1980 to 2004, this paper investigates the variability of winter snow/rainfall in northern China and the associated atmospheric circulation and aerosol distribution characteristics by using composite analysis. The results show that winter precipitation in northern China has been generally increasing since the 1960s. Among the winters of 1990–2008, the years with more rain/snow (MRSYs) are 1998, 2003, and 2006, while the years with less rain/snow (LRSYs) are 2005, 1997, and 2001. Composite analysis finds that the main differences of atmospheric circulation in East Asia between MRSYs and LRSYs are as follows. 1) In MRSYs, strong low-level cold air over the northern polar region and Taymyr Peninsula migrates southward to northern China (Northwest, North, and Northeast China), establishing a channel favoring continuous southward transport of cold air. In LRSYs, however, this cold air channel does not exist. 2) In MRSYs, the frontal zone and westerlies are over North China, and the low-level geopotential height field from eastern China to West Pacific exhibits an “east high, west low” pattern, which is conducive to easterly and southerly airflows moving northward along 110?E. In LRSYs, the 500-hPa prevailing westerly winds stay far away from China and the low-level southeasterlies move to higher latitudes, which are disadvantageous to the development of precipitation in northern China. 3) In MRSYs, large-scale upward motions combined with local-scale updrafts develop into strong slanted climbing airflows, forming a vertical circulation that favors the generation of heavy snows in eastern China. In LRSYs, the vertical circulation moves eastward into the Pacific Ocean. Furthermore, the correlation analysis on AOD and winter precipitation during the period 1980–2004 in northern China reveals that AOD differs significantly between MRSYs and LRSYs and the annual variation of winter rain/snow is positively correlated to the annual variation of AOD with a correlation coefficient of 0.415 at the 0.001 significance level.