Formation mechanism for the atmospheric environment of North Blizzard in November 2009

From Nov. 09 to Nov. 12, 2009, a large range of rain and snow process with low-temperature occurred in North China (named “0911” Blizzard in North China hereafter), it caused severe disasters and losses in the region. The purpose of this paper is to explore the mechanism of the process by analyzing atmospheric conditions. The results show that the warm stratus provided favorable conditions for this strong rainfall and snowfall process; before snow occurred, a hot and humid environment provided a favorable temperature and humidity field to accumulate energy for the process in the lower atmosphere (850hPa); the northern cold air outbreak and invasion southward is the trigger mechanism of warm stratus forming; a large amount of latent heat of condensation generated in the lower atmosphere (850hPa), which would boost to vertical movement easily. when water vapour transportion strengthen in the middle atmosphere (700hPa), water vapour condense and grow, and then forming warm stratus.