关键词: 中国西南, 春季, 持续干旱, 大气环流, 海温

Abstract: With 44 stations temperature and precipitation data of day by day in Southwest China，NCAR / NCEP monthly mean height field，wind，surface pressure，specific humidity，vertical speed，and NOAA monthly mean sea surface temperature data，the potential evaporation was calculated by Thornthwaite method. Through analyzing monthly precipitation and potential evaporation percentage proportion spring precipitation from March to May.and taking into account the precipitation and potential evaporation of April and May accounted for the major part of the spring，we selected the period of April and May as our research subject and by using homogenization drought index of precipitation and potential evaporation，the persistent drought of spring was defined at first in Southwest China，and then the abnormal years of the persistent drought were determined. By Synthetic analysis method，the atmospheric circulation features of persistent drought over Southwest China from April to May was analyzed. Influence prophase sea surface temperature of Indian Ocean region on persistent drought over the southwest China from April to May was discussed，The results showed that: in the persistent drought years from April to May over Southwest China，Ural ridge was weak clearly，the southern section of East Asian trough and south branch trough leaned weak over the same period from April to May，but leaned strong westerly in middle and high latitudes，thus the northern cold air of Southwest China's influence leaned weak，and the southwest warm and wet air transported to southwest China was also weak. Correspondence vertical movement showed the abnormal downward motion over Southwest China,,at the same time the moisture transport flux showed abnormal divergence center，the circumfluence led to drought in the Southwest China. and this circulation features had good continuity from April to May，So persistent droughts occurred over Southwest China in spring. In addition，from the beginning of February in the Indian Ocean sea，we observed that the surface temperature display changed. In persistent drought years from April to May over Southwest China，the warmer sea surface temperature anomaly area was gradually moving eastward from the previous February in the Indian Ocean and reached to the Eastern Indian Ocean in April-May，and the anomaly warmer sea surface temperature heated the atmospheric in Eastern Indian Ocean，leading to an abnormal upward motion over Eastern Indian Ocean and Hadley circulation enhancement，But the abnormal downward motion over Southwest China eventually led to drought phenomenon occurred from April to May in Southwest China. This might be the primary mechanism Pre-Indian Ocean sea surface temperature which influenced the spring persistent drought of Southwest China. Of course，cause of persistent droughts over Southwest China is complicated，for example，Pacific sea surface temperature also affected the persistent droughts over Southwest China,for the water vapor source of Southwest China comes part from the Indian Ocean，part from the Pacific. But what’s the main factors needs further study and analysis. However，the research provides  some references for short-term climate projections of spring persistent drought phenomena over the Southwest China.

Key words: southwest China, spring, persistent drought, atmospheric circulation, SST