The following are the main characteristics of the general circulation of atmosphere in May 2011. There are two centers of the Northern Hemisphere polar vortex and four waves around the earth in middlehigh latitudes. More troughs occur in middle-high latitudes in the Asian area, and lead to several streams of cold air which influence China. The East Asia major trough is stronger than usual at same time period. The subtropical high and the southern branch trough are near climatological normals. The monthly mean temperature averaged over China is 17. 7℃ which is 0. 3℃ higher than climatological normals, and the monthly mean precipitation averaged over China is 81.4 mm which is 12. 1% less than climatological normals （92.6 mm）. There are two cold airs, seven precipitations and one strong sand-dust process in May 2011 respectively. Rain storm and flooding occur in Sichuan, Hunan, Guangdong, Guangxi, etc. Meanwhile, the drought continues developing at the middle and lower reaches of the Changjiang River. Strong wind and hail disasters hit Xinjiang, Gansu, Ningxia, Hebei, Shandong, Hunan, Guizhou, Guangdong, etc.%2011年5月大气环流主要特征如下：北半球极涡呈现双极型,北半球中高纬度环流呈脱四波型分布,亚洲中高纬地区西风带多波动,引导多股冷空气影响我国;东亚大槽较常年同期略偏强,西太平洋副热带高压及南支槽强度接近常年同期。2011年5月,全国平均气温为17.7℃,比常年同期（17.4℃）偏高0.3℃。5月全国平均降水量为81.4 mm,较常年同期（92.6 mm）偏少12.1%。月内共出现两次冷空气过程,7次明显降水过程及一次强沙尘暴过程,长江中下游地区气象干旱持续发展,四川、湖南、广东、广西等地遭受暴雨洪涝灾害
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