The temporal characteristics and the atmospheric circulation characteristics for spring drought and rainy climate in Inner Mongolia

The precipitation data in spring( March- May) 1960- 2011 were collected from 104 weather stations and NCEP /NCAR reanalysis data and precipitation anomaly percentage were used to evaluate the drought and rainy climate characteristics and analyze the regional temporal atmospheric circulation features in drought years and rainy years. The outcomes prove: In spring,eastern region and southern regions had higher precipitation than western and northern regions. Eastern agricultural areas and northern pastoral areas experienced more drought years; Northeastern agricultural areas and forest areas were recorded having significant higher number of rainy years; Mid- western agricultural areas and cities met similar numbers of drought and rainy years. The whole regions leaned to be dry before 1990 s,meanwhile tended to be rainy from 2000 to 2011. Nonetheless,the record of abnormal precipitation significantly increased after 1990 s. In drought years,500 hPa anomalies and middle and high latitudes Eurasian anomalies were in - +- distribution. 850 hPa radial wind anomalies presented that in drought years,northwest flow controlled the West Asia and South Asia; the strong cold air mass prevented the transportation of southwest warm air towards north. In rainy years,southerly anomaly covered the areas from Bay of Bengal to Eastern Russia,with strong southwest airflow upon westerlies; southwest warm air towards northerly. In pre- drought period,Ural ridge became powerful,East Asian trough positions westerly;Trough is on Lake Baikal. In pre- rainy period,Ural ridge became weak,East Asian trough positioned easterly;Ridge was on Lake Baikal.