Variation Characteristics Of Local Meridional Circulation Over Asia And Its Influence On The Rainfall In The Yangtze River Basin

Using the NCAR/NCEP reanalysis data for the period of 1979-2009, with mass stream function and statistical analysis method, the structure and variation characteristics of the Asian local meridional circulation of three areas, and its corresponding period or lag influence on rainfall and characteristics of water vapor transportation in Yangtze River Basin are analyzed. Further, the relationship and mechanistic of the influence are studied. The results are shown as follows:(1) The existed annual variability of the Asian local meridional circulation is similar to MMC, but the shape of circulation has local characteristics. There are some differences in the establish condition and structure of meridional circulation over two longitude zones. The shape of mass stream function answers to the location and seasonal variation of direct cell or counter cell. The meridional circulation index has inter-annual or inter-decadal variability, but its long-term trend is not obvious.(2) By changing the characteristics of meridional water vapor transportation, the meridional circulation of East-Asian subtropical in Summer have positive correlation of corresponding period with the rainfall over Yangtze River basin, which means that when the circulation is stronger(weaker), moisture flux divergence is convergent(divergent),the rainfalls become more(less).(3) With the change of the characteristics of meridional and latitudinal water vapor transportation, the meridional circulation of the South Asia in May have negative correlation with the rainfall in Yangtze River basin in July. Which means that when the circulation is stronger (weaker), moisture flux through south boundary and west boundary is less (more), the rainfalls become less (more).(4) With the change of the characteristics of meridional and latitudinal water vapor transportation, the relationship between the meridional circulation of Tibetan Plateau in May and rainfall in Yangtze River basin in July is out-of-phase with the meridional circulation of the South Asia. Which means that when the circulation is stronger(weaker), moisture flux through South boundary and west boundary is more(less), the rainfalls become more(less).(5) The negative correlation between the meridional circulation of the South Asia and Tibetan Plateau is stronger in summer, and the meridional circulation of the South Asia has corresponding period or lag negative correlation with East-Asian subtropical also. Local meridional circulations in different areas are connected by circulation background and effect mechanism of SST, which influence on rainfall and characteristics of water vapor transportation in Yangtze River Basin.