Analysis of Characteristic and Causes of a Strong Cooling Process in China in the Early Winter of 2020/2021.

The characteristics and causes of a drop in temperature during a cold wave process in the early winter of 2020/2021 were analyzed. The results show that the air temperature at 700 -600 hPa over China was firstly and mostly influenced by the cold wave process, and then the cold air gradually extended to the lower layer, causing the most severe cooling in North China and its nearby areas. During the cold wave, the longitude of the upper-level jet over the Chinese mainland was larger; the Ural blocking high and the East Asian trough were stronger, so that the geopotential height gradient between the two was also significantly larger; the meridional air flow was abnormally strong, which was conducive to the southward transport of cold air from the middle and high latitudes. Results of the diagnostic analysis further show that the outbreak of the cold wave and the negative temperature tendency anomaly in the key area were mainly caused by the meridional temperature horizontal advection anomaly, while the temperature rise accompanied by abnormal air subsidence compensated for the abnormal decrease in temperature, which was conducive to the gradual rise of temperature in the key area. [ABSTRACT FROM AUTHOR]