Leading Spatial Patterns of Summer Rainfall Quasibiennial Oscillation and Characteristics of Meteorological Backgrounds over Eastern China

In virtue of empirical orthogonal function (EOF) analysis and correlation analysis etc., the leading spatial patterns of summer rainfall quasi-biennial oscillation and the meteorological backgrounds are analyzed using data of monthly total rainfall of China at 160 stations during 1951~2005 from China Meteorological Administration and NCEP/NCAR reanalysis datasets. The result shows that the seasonal variation of rainfall is significant over China and summer is the main stage of rainfall. Summer rainfall has a noticeable character of tropospheric quasi-biennial oscillation (TBO) and eastern China has the maximum rainfall TBO variance. The summer rainfall TBO has two leading EOF spatial modes over eastern China. One reflects the reverse phase of rainfall evolution between south and north of around 27°N and the rainfall amplitude is relatively large. The other has a relatively small rainfall amplitude with the high value center in the belt from Hetao to North China. The meteorological backgrounds that form the two modes are different. The first mode has positive correlation with the West Pacific ocean surface temperature anomaly (SSTA) and negative correlation with the East Pacific SSTA while the second mode has positive correlation with the Japanese Sea SSTA. When the summer rainfall TBO increases in the Yangtze-Huaihe river basin, following the first mode, the West Pacific SST is higher and the East Pacific SST is lower than that in normal periods, and 850 hPa has an anticyclone anomaly over eastern China and its coast areas. The correlation field between the first model and 500 hPa height anomaly presents a “+-+” pattern over East Asia. The South Asia High strengthens at 200 hPa and the position of the west jet moves south to the average. When the position of the summer rainfall TBO moves north, following the second mode, 850 hPa has a cyclone anomaly over eastern China and its coast areas, the South Asia High weakens at 200 hPa and the position of the west jet moves north to the average.