Analysis of the January 2013 Atmosphere Circulation and Weather
The main characteristics of the general circulation of atmosphere in January 2013 are as follows: There are two polar vortex centers in the Northern Hemisphere with weaker strength and smaller scopes than normal years. Three waves appear in middle high latitudes. The Eurasia trough is located over West Siberia being farther north and leads to several streams of cold air to influence the north of China. The circulation in middle high latitudes varies from meridional circulation in the first dekad to the zonal circulation in the middle and last dekads of January. The subtropical high is near climatological normals. The East Asia trough is clearly stronger than usual. The south branch trough around 90°E is slightly weaker than the normal years. Monthly mean temperature in January over China is -5.2℃， 0.2℃ lower than the corresponding period of normal years. However, the 1st ten day mean temperature in January is 3℃ lower than the normal while, the last ten day temperature is 1.7℃ higher. Monthly mean precipitation (6.5 mm) is 50.8% less than the normal (13.2 mm). One cold surge process and three large scale haze and fog processes are experienced in this month. Low temperature, sleet and freezing rain hit the south of China while a snow disaster occurs in the north of China. Drought still continues in Yunnan, western Guizhou and southern Sichuan and some other places.