Summer Arctic Oscillation (ao), The East Asian Summer Monsoon Precipitation Of Eastern China Interdecadal Variations

Using the NCEP/NCAR reanalysis data, we test the Arctic Oscillation (AO) mode. Through the research, it is found that the AO mode in winter has a deep equivalent barotropic signature from the ground to tropopause, and it has a baroclinic signature in summer. AO mode haves the obvious seasonal variability. From winter to summer, the height of AO mode's conversion becomes low, and the pleion in the boreal Pacific moves from the ocean to the East Asian land. Furthermore, from summer to winter, the height of mode's conversion becomes high, and the pleion moves from the land to the ocean. The position of pleion in the Atlantic changes little all the year, but its extensity and intensity change with season. Its extensity is wide in winter and narrow in summer, and its intensity is strong in winter and weak in summer. Both winter and summer AO indexes have abrupt changed at 1976. The position and extensity of winter AO mode's anomaly center change little, but the intensity becomes stronger after the abrupt change. In addition, the summer AO mode changes much between before and after the abrupt change, especially the pleion in the East Asian land. Its intensity becomes weak and its extensity becomes narrow after the abrupt change, which shows the East Asian summer monsoon (EASM) has obviously declined trend after 1976.There is the anticorrelation between the summer AO and EASM, especially in the interdecadal variability. From the Singular Spectrum Analysis' (SSA) reconstructed time series of summer AO and EASM indexes, we can find that their interdecadal variability has tight anticorrelation; however, their interannual change's correlation is very low. At the same time, we study the summer AO and ESAM index' abrupt change time, and we can conclude that AO and EASM index both have an abrupt change at the middle-later period of 1970's.There are close contemporary correlation among the summer AO, EASM and the rainfall at East of China's interdecadal variability. Owing to the strong anticorrelation between AO and EASM's interdecadal variability, AO is stronger (weaker), at the same time, EASM is weaker (stronger). With the impact of them, the rainfall at the Yangtse Valley is more (less) and the precipitation at North China is less (more). There is a significant area at Yangtse Valley in the partial correlation map between summer AO and the rainfall at the East of China, and there is a significant area at North China in the partial correlation map between EASM and the rainfall at the East of China. As a conclusion, the law of AO and EASM's interdecadal variability, can help us to forecast the rainfall at East of China in summer.