Interannual variability of summer climate modeover East Asia and its mechanism

Interannual variability of the dominated summer climate(rainfall and temperature)patterns over East Asia(China and Japan)and its mechanism are studied. It is found that there is a strong coupling between the large-scale summer rainfall and temperature variations in China on the interannual time-scale. Large-scale above (below) normal rainfall variation generally corresponds to large-scale below(above) normal temperature variation. The long-term variation of the first pattern of singulu value decomposition mainly reflects the increasing(wetting) trend of rainfall and decreasing (cooling) trend of temperature year by year over the middle reach of Chartgjiang River. The component of quasi-biennial oscillation variation is intensified after the middle of 1970s in the coupling variation of rainfall and temperature. It is noticeable that the summer rainfall variation is the exactly biennial oscillation variation in the middle reach of Changjiang River and the Great Bend of Huanghe River after the middle of 1980s. Therefore, there is a trend of time scale shortening in the interannual variation of the summer rainfall in the middle reach of Changjiang River and the Great Bend of Huanghe River. It is found that the large-scale background anomaly in affecting the rainfall and temperature anomalies along the middle and lower reaches of Changjiang River is coherent, that is,the two teleconnection pattetns:the Pacific-Japan(PJ) and Eurasia teleconnection patterns. The rainfall and temperature anomalies along the middle and lower reaches of Changjiang River,connected with the plum rain anomaly in East Asia in summer, is the result of the interaction between the cold and dry air from the temperate and high latitudes and the warm and moist air from the low latitudes. The interannual variations of sea surface temperature anomaly and the connected convective activity in the tropical western Pacific affect significantly the interannual variations of the summer rainfall and temperature in East Asia through the PI teleconnection pattern. There is obvious seasonality of the interaction between the convective activity over the western Pacific and the teleconnection patterns of the general circulation in the Northern Hemisphere (NH).The PJ pattern is not only the most important pattern in the coupled interaction between the interannual variabilities of the convection over the western Pacific and the extratropical general circulation in the NH summer, but also the dominant pattern in the variations for themselves. Through the principal oscillation pattern analysis of the 500 hPa geopotential height in the NH summer of 1984,it is indicated that the energy can propagate from the tropical western Pacific to the northern part of East Asia through the PJ-like oscillation. The impact from the low latitudes can reach 70°N. At the same time,there is also the propagation of energy from the high latitudes to the low latitudes, that is, from the North Pole to 70°N. The impacts from the low latitudes and from the high latitudes are converged around 70°N.