Snowfall over central-eastern China and Asian atmospheric cold source in January

摘要

In January 2008, a severe snowstorm disaster occurred in central-eastern China. Using the monthly means from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data set and the observations from surface stations of China for the period 1953-2008, we statistically investigate the relationship between the January snowstorm weather over central-eastern China and the synchronous atmospheric thermal condition over the Asian continent. The results show that the extreme snowfall weather over central-eastern China is closely associated with the Asian atmospheric cold source (AACS) in January. When AACS is weak (corresponding to a higher AACS value), the heavy snowfall weather appears in central-eastern China. The values of both AACS and snowfall over central-eastern China in 2008 are most anomalous during the recent 30 years. This link may be explained by the atmospheric circulation well. Under a weak AACS (with a higher AACS value), a 500-mb anomalous low covers the mid-low latitudes of Asia, accompanying an anomalous high over the eastern coasts of East Asia. Accordingly, the southerly wind anomalies between the anomalous low and high prevail in the lower troposphere over central-eastern China, with the northerly wind anomalies prevail over this region at the surface, which also strengthen upward motion over central-eastern China. The southerly wind anomalies transport more water vapour into central-eastern China from both the South China Sea and the Bay of Bengal. These anomalies in the atmospheric circulation are responsible for the formation of the heavy snowfall weather in central-eastern China. Compared to both the El Ni?o-Southern Oscillation and Arctic Oscillation during winter, the thermal condition over the Asian continent has a closer relationship with the occurrence of the heavy snowfall weather over central-eastern China.