The large scale circulation of the snow disaster in south China in the beginning of 2008

This study analyzed the heaviest snowfalls and icy rainfalls occurring in southern China from January to the beginning of February 2008. The results are summarized as follows: the disaster was associated with a persistent front of warm/cold air mass in southern China. It was result of the interaction between the weather systems in high latitudes and low latitudes. In mid January 2008,the AO index changed from negative to positive, indicative of an adjustment of hemispheric circulation. The long lasting precipitation well coincided with a blocking situation nearby 80°E during mid January to early February. A diagnostic analysis indicates that the energy dispersion accompanying the blocking high compelled stationary waves to propagate from high latitudes to the south of the Yangtze River, which maintained as an energy source for the cyclonic circulation in situ. Under the control of the massive blocking high, cold air from high latitudes could march southward on a large scale, but continuously pervaded into the south. On the other hand, the SST in the western Pacific warm pool rose up constantly since the onset of the strong La Nina episode, which provided a source for warm and moist air. The blocking high collapsed around 30 January and the energy source for the local cyclonic circulation was cutoff. Thus, the precipitation in southern China stopped after 1 February.