Analysis of the December 2014 Atmospheric Circulation and Weather
The main characteristics of the general atmospheric circulation in December 2014 are as follows: The polar vortex of the Northern Hemisphere is stronger than the normal. The Eurasia mid high latitude circulation presents the trough ridge trough pattern. The East Asian major trough is stronger, causing cold airs to be very active. The south branch trough is located near 70°E, being obviously more westward than in the same period of normal years, so not favorable for the water vapor transport to eastern China. The subtropical high is stronger, located more westward and northward than in normal years. The monthly mean precipitation over China is 7.9 mm, which is 24.8% less than the normal value (10.5 mm). Especially in Huabei, Huanghuai, Jianghuai, Jianghan regions, the precipitation amounts decrease 80% of the normal. The monthly mean temperature over China is -3.4℃, 0.2℃ lower than normal (-3.2℃). The temperature changes greatly in this month showing the characteristics of being cold in early and midmonth but warm later. There are five cold air processes, four fog haze processes and one large range rainfall event over China in this month. Many places in the north experience extreme daily temperature dropping events, and some areas of northeast China suffer snow disasters. Meanwhile, wide range of fog haze weather persists in the 2nd and 3rd dekads this month.