Three dominant synoptic atmospheric circulation patterns influencing severe winter haze in eastern China

Abstract. Previous studies indicated that, on synoptic scale, the severe haze in eastern China (EC) is affected by the atmospheric circulation variations. However, it is still unclear what are the dominant atmospheric circulation patterns influencing the severe winter haze conditions in EC and what are the differences between them. To systematically determine the dominant synoptic atmospheric circulation patterns of severe haze in different regions of EC, we use the Hierarchical Clustering Algorithm to classify the local geopotential height anomalies at 500-hPa over the stations with severe haze and obtained three dominant synoptic atmospheric circulation types based on observed PM2.5 concentration and NCEP/NCAR reanalysis. Circulation Type1 is accompanied by significant north wind component anomalies over northern China and causes severe haze pollution over the Yangtze River valley. Although the local meteorological conditions are not conducive to haze formation and accumulation, the severe haze in Yangtze River valley is related to the pollution transportation caused by the north wind anomalies. During the haze days with circulation Type2, the joint affection of East Atlantic-West Russia teleconnection pattern and winter East Asia subtropical jet stimulate and maintain the anticyclonic anomalies over northeast Asia, which provides meteorological conditions conducive to the occurrence of severe haze over the whole EC. The circulation Type3 mainly caused severe haze events in northeast China through the establishment of blocking high over the Okhotsk Sea. The results provide a basis for establishing haze prediction and management policies applicable to different regions in EC.