Analysis of the December 2011 Atmospheric Circulation and Weather

The following are the main characteristics of the general circulation of atmosphere in December 2011:There is one polar vortex center in the Northern Hemisphere with a slightly stronger strength than normal years.The circulation presents a four-wave pattern in middle-high latitudes.The west European major trough is stronger and the East Asian major trough is weaker than the same period of normal years. The positions of the south branch trough and the northeast subtropical high are approaching to those at the same period of normal years,but the strength is weaker.This kind of situation is not favorable for the transportation of water vapor.There are two cold surge processes affecting China,and the monthly mean temperature is -3.8℃,which is slightly higher than that(-3.9℃) at the same period of normal years. In this month,the mean precipitation(7.5mm) is 23.5%less than normal.The precipitation amounts of Liaoning Province,west of Jilin Province,southeast of Inner Mongolia,Guangdong Province,west of Qinghai Province,and middle of the Tibet Autonomous Region are all 80%less than the same period of normal years.