부산대학교 도서관

Interannual variability of the East Asian summer monsoon affects the distribution of regional rainfall, thus it is a very important scientific problem. The ECMWF data from March to July for 1983, 1985, 1991 and 1992 are used to investigate the characteristics of the East Asian summer monsoon in the Yangtze and Huaihe Rivers (June-July) and in Taiwan area (May-June). The spatial distribution of several important components related to the interannual variability of the East Asian monsoon are examined especially the upper-level thermal effect. It is found that the phase of Mei-Yu rainfall between the Yangtze-Huaihe River valley and Taiwan is out of phase, when 500 hPa western Pacific subtropical high prevails continuously stronger or weaker. However, when the influence of irregular development of the western pacific subtropical high that possess differently positive or negative anomalies in May and June, then those two areas rainfall have in phase correlation. According to the time series's analysis, the reversal of the meridional temperature gradient (5°N-25°N) occurs first over the longitudes east of 85°E and then over the longitudes west of 85°E at the upper troposphere. The heating structure is responsible for the dramatic change of two stages of the upper-level westerly jet, the South Asian anticyclone and the low-level southwesterly. When the Yangtze-Hualihe River vally is dry, the South Asian anticyclone doesn't establish until the warming process of the first stage occurs and move westward rapidly. In the dry year, the upper-level westerly jet jumps continuously northward even in the second stage of heating. But it is not so in the wet year. This is the distinct difference between the dry and wet years. Besides, the length of warming period is also potentially responsible for the interannual variability of rainfall between the Yangtze-Huaihe River valley and Taiwan.