A preliminary investigation on causes of the catastrophic snowstorm in March, 2007 in the northeastern parts of China

A snowstorm deposited record breaking snowfall over the northeastern parts of China on March 3-5, 2007, resulting in severe disasters and heavy losses. The objective of this study is to explore the possible mechanism responsible for this extreme event by analyzing the atmospheric circulation anomalies prior to and during the event. The results show that there had been persistent strong anomalous Arctic Oscillations, Antarctic Oscillations, Eurasian teleconnection pattern, and North Pacific Oscillations in about two weeks before the event. Those anomalous atmospheric circulations stimulated the strong anomalous southerlies along the east coastal regions of China, which persistently transferred the warm and wet air to the northeastern areas of China, thus raising the moisture content and air temperature there and providing proper warm and wet conditions for the occurrence of the extreme snowstorm event. When the atmospheric general circulation changed in early March, the strong cold air from the high latitudes met the warm air over the northeastern China, resulting in a remarkably cold front and associated strong snowfall and low temperature in that region.The results of this study imply that the anomalous atmospheric circulation and the cumulative moisture condition in the forecast region in the early stage should be fully considered, which is helpful to the improvement of rainfall forecast, especially the heavy rainfall forecast.