Abstract:

Based on the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) daily reanalysis data and the temperature data collected at conventional observation stations from the National Meteorological Information center, the characteristics of the large-scale extreme cold events in China were analyzed.The national extreme low temperature events were defined based on intensity, range and time, and thirty-eight large-scale extreme cold temperature events (LECES) were obtained, which were divided into five types according to different affected regions:national, Eastern, South and North China, Northwest and South China, and Northeast China.The circulation backgrounds of different styles of the LECES were also analyzed.The results show that there are precursor signals about 15 days before the occurrence of the nationwide LECES.An obvious blocking situation appears in the Ural Mountains.The upper-level jet stream at 300 hPa shows zonal direction in positive and negative, which strengthens the circulation system of East Asian monsoon and Siberian high, and the cold air accumulates in northern Asia.An extraordinarily strong anticyclone covers Siberia at 850 hPa, and most of China is controlled by northerly winds.Such a spatial configuration and evolution of circulation system in the middle and lower troposphere affects China and causes extreme cold temperature events.Besides, compared with the nationwide LECES, the other types of LECES have the precursor signal about five days before the event, with short duration and weak intensity.And the anomaly area of 500 hPa height field and sea level pressure field determines the type of LECES.

Key words: Extreme cold events, Nationwide LECES, Circulation backgrounds