SEASONAL VARIATION FEATURES OF 500 HPA HEIGHT IN NORTH PACIFIC OSCILLATION REGION AND ITS EFFECT ON PRECIPITATION IN NORTHEAST CHINA

By using of the China National Climate Center (CNCC) 500 hPa monthly mean height data (10°×5°) from 1960 to 2000 and EOF, SVD methods, the 500 hPa seasonal variation characteristics of the 500 hPa height field in the North Pacific Oscillation (NPO) region (25° to 70° N, 140° E to 150° W) region and its relation with precipitation in 80 stations over Northeast China are analyzed. The results show that: (1) In winter, the spatial structure of the first loading vector of the 500 hPa height field in NPO, similar to the positive phase of the surface pressure oscillation, is of a "﹣, +" wave distribution from north to south with the variance contribution ratio being 40%. This is a basic general circulation mode in the mid-high latitudes of North Pacific in 40 years with the East Asia Trough being a stationary wave, and it is also the main cause that NPO is mostly in positive phase. Otherwise, it is similar to the negative phase of the surface pressure oscillation. The second loading vector is of a whole "+" value distribution with the variance contribution ratio being 28%. This mode is an abnormal pattern opposite to the climatic basic mode, a long-wave ridge as a substitute for the East Asia trough. In summer, the first loading vector is of a whole "+" value distribution with the variance contribution ratio being 30%; the third is of a "+, ﹣" wave train from north to south with the variance contribution ratio being 13%. This indicates that the summer 500 hPa height NPO is not the main mode. There is a clear NPO mode in both spring and autumn. (2) There is significant correlation between the 500 hPa mean winter height field in the NPO region and summer precipitation over Northeast China (>0.01) with a "+, ﹣" wave train from north to south. The first SVD singular vector has a variance contribution ratio of 49%. The summer precipitation over Northeast is above the normal when the 500 hPa height field in the NPO region in the previous winter is in negative phase, but it is dry when the 500 hPa height is in positive phase. There is similar relationship in other seasons.