Decadal Shift Of Dominant Mode In North Pacific Sst And Its Possible Impacts On East Asian Monsoon In Winter

The present study utilized the 160 station-observed precipitations in China, NECP/NCAR atmosphere reanalyzed datasets, as well as the Hadley SST datasets, and discussed the possible reasons responsible for the regime shift of dominant mode in winter North Pacific sea surface temperature(SST), and its impacts on winter South China rainfall anomalies, by virtue of EOF, time-phase EOF, linear analysis, and the Atmosphere General Circulation Model of ECHAM5. The main conclusions are summarized as follows:(1) The shift between PDO and NPGO after 1990 is resulted from the internal and external impacts of Ocean and atmosphere in North Pacific. Analyses suggest that the negative correlation between the changes of SST in northern(44?-49?N, 151?-177?W) and central(28-36?N, 152?-178?W) North Pacific may results in the dominant mode of NPGO. The enhanced North Pacific Oscillation(NPO) however, plays an important external forcing on the basis of wind-driven oceanic current theory;(2) The PDO and NPGO are closely coupled with the upper atmosphere, which is characterized by the enhanced Aleutian Low(AL) and NPO, with westerly winds anomaly near 30?N and 40?N in the North Pacific, respectively. The polarward shift of tropospheric westerly winds plays an important role modulating the climate variability in East Asia. The deficient rainfall is found in South China with respect to the positive phase of NPGO after 1990;(3) The ECHAM5 model-simulated results suggest that both eastern tropical Pacific and subtropical SST in the PDO mode play the same important role in the climate change in North Pacific. However, the central tropical Pacific SST anomalies are more important in the NPGO mode. Modeling suggests that the NPGO mode is possibly responsible for the change of rainfall in South China after 1990.