Diagnostic Study on the Characteristics of East Asia Summer Monsoon in Different Phases of ENSO Cycle

The variation of East Asia summer monsoon in different phases of ENSO cycle has been analyzed by using reanalysis grid data from NCEP/NCAR, sea surface temperature data from NCAR and ground surface temperature data from observational station of China. The effect of abnormal SST on East Asia summer monsoon has been discussed through the variation of land-sea thermal difference and monsoon low pressure. The results show that there are obvious yearly and decadal changes in East Asia summer monsoon index, and there is also good negative correlation between the index and SST in east equatorial Pacific. The East Asia summer monsoon index is bigger in the period after three months of cool Nino1+2 SST than that after the warm Nino1+2 SST. There are also obvious variations of land surface temperature and sea level pressure in Asia continent when east equatorial Pacific SST changes. In the summer, after three months of warm Nino1+2 SST, the land surface temperature is lower in the area north of Yangtze River, the sea level pressure in Asian continent is higher, as well as the summer monsoon depression in Asia is weakened. It is contrary in the case after cool Nino1+2 SST. That means, the oscillation of sea level pressure induced by east equatorial Pacific SST anomaly appears not only in the oceans, but also in the continents. It should be the main reason that leads to the variation of East Asia summer monsoon in different periods of ENSO cycle.