利用1961-2010年NCEP/NCAR全球逐月资料， 对云南4次极端干旱年春季（3-4月）的大气环流特征与多雨年春季的大气环流特征进行了合成对比分析。结果表明， 云南极端干旱年春季与多雨年春季的大气环流特征有明显的差异。干旱年， 500 hPa高度距平场上欧洲、 亚洲以40°N为界北负南正， 南支槽偏弱, 地面西伯利亚高压偏弱； 700 hPa中纬度为西风距平， 西风带偏强\, 气流平直， 以纬向环流为主， 低纬地区孟加拉湾、 中南半岛有异常反气旋环流， 整个对流层为下沉运动。降水偏多年, 500 hPa高度距平场上欧亚中高纬西低东高， 亚洲以38°N为界北正南负， 南支槽偏强, 地面西伯利亚高压偏强； 中纬度为东风距平， 西风带偏弱， 环流经向度较大， 低纬地区中南半岛北部到云南为异常气旋环流， 对流层中低层为上升运动。水汽通量的多年平均表明, 影响云南的水汽是南支西风水汽输送带和西太平洋副热带高压外围的水汽输送带在云南上空交汇。干旱年, 两支水汽输送带上的水汽通量辐合弱， 云南上空水汽含量减少； 降水偏多年, 两支水汽输送带上的水汽通量辐合强， 特别是西太平洋副热带高压外围的水汽输送带辐合强， 云南上空水汽含量增加。干旱年, 中高纬的冷空气难以影响到云南， 低纬下沉气流和水汽通量辐合弱, 使云南产生降水的动力条件和水汽条件均不足; 而多雨年则相反， 产生降水的动力条件和水汽条件均有利。同期AO指数与云南春季气温呈负相关, 与降水呈正相关\.AO为负位相时云南高温少雨， 易出现春旱， 有利于极端干旱的发生。

Using the NCEP/NCAR reanalysis data  from 1961 to 2010, the difference of atmospheric circulation in spring between the extreme drought and rainy years (from March to April) in Yunnan were analyzed. The results show that the characteristis of atmospheric circulation in rainy spring are different from that of in spring of drought year. In the extreme drought years, it is negative anomaly in the region of the north of 40°N but positive in the region  of the south of 40°N on 500 hPa geopotential height field. The south branch trough and  Siberian high pressure are weak in the extreme drought year. The atmospheric circulations are characteristic of strong westerly and zonal circulation on 700 hPa in the Eurasia mid-latitude. There is an abnormal anticyclone over the Bay of Bengal and the South Peninsula, which lead the sinking motion in the troposphere. In the rainy years, it is positive anomaly in the region of the north of 38°N but negative of the south of 38°N on 500 hPa geopotential height field. The atmospheric circulations are characteristic of weak westerly and meridional circulation on 700 hPa in the Eurasia mid-latitude. The south branch trough and Siberian high pressure are strong in the rainy years. There is an abnormal cyclone from north of  South Peninsula to Yunnan, which lead the ascending motion in the troposphere. Water vapor transportation over Yunnan comes from the vapor transportation of south branch westerly and  water vapor transportation of west Pacific subtropical high external vapor transportation. Both of the two water vapor transportation are weak, resulting in the reducing of the vapor content   over Yunnan in the extreme drought years. On the other hand, the convergence of those two branch vapor transportations are strong, especially stronger in the  of water vapor western Pacific subtropical high external, increasing the content of the water vapor in the rainy year. The weak cold air, the sinking air flow and the weak convergence of water vapor flux, which lead to the poor dynamical conditions and weak water vapor transportation, are the reasons of extreme drought in Yunnan. The AO index  is negative correlation of the temperature in Yunnan in spring but positive correlation of the precipitation. In the negative phase of AO index, the temperature is higher and the precipitation is less in Yunnan, the spring drought is obviously, which is helpful to  the development of extreme drought.