Interdecadal Variation Of Summer Precipitation In East Asia In The Late 1990s And Its Mechanism

Under the interaction of the natural variabilities and human activities, the summer climate in East Asia, especially the summer precipitation, showed significant changes in the characteristics of interdecadal variation. In the late 1990s, the summer precipitation in East Asia, there is also a very significant interdecadal variability. So in this paper, the commonly methods used in meteorology mainly include correlation analysis, wavelet transform, the synthetic analysis of the similarity coefficient and EOF decomposition. The article focuses on the study of temporal and spatial characteristics of the precipitation interdecadal variations during the summer of late-1990s in East Asia, and the corresponding circulation variation characteristics and features of water vapor transmission characteristics and external force mechanism. The main conclusions are as follows:(1) The summer precipitation in northern East Asia experienced a notable interdecadal change in the late 1990s, mainly from wet to dry, and the summer precipitation in southern East Asia experienced interdecadal changes in the early 1990s and in the 21st century, from dry to wet to dry. From the angle of the East Asian region of macroeconomic performance for rain type "+-" to "-+" model transformation, at the same time, the interdecadal variability of summer precipitation characteristics in the northern East Asia is obvious to the interdecadal variability of summer precipitation characteristics in the southern East Asia.(2) The summer circulation of East Asia also experienced interdecadal change in the late 1990s. Its direct cause is the interdecadal anomalies of summer circulation present north-south inverting dipole model. Such as:the interdecadal change in northern Eurasia height field distribution of the form "a ridge of the two slot", from south to north in East Asia to present"-+" dipole distribution is helpful to form the blocking high frequency in central Asia; 850 hPa wind field in the northern East Asian presents anticyclone, and U200 wind field is convergence, southern East Asia to form a cyclone; The layer of water vapor transportation in northern East Asia regional anti cyclonic anomaly, water vapor transmission of divergence, southern region to form a cyclonic anomaly conveying, water vapor transmission convergence, is advantageous to the precipitation in southern East Asia region. At the same time, the two East Asian summer monsoon index EAP and EASM index shows the East Asian summer monsoon intensity in the middle of the 20th century there is an obvious decadal variability. At the same time in the northern Pacific and the western Pacific SST cooling in the late 1990s. By correlation analysis of the northern Pacific SST and the western Pacific SST index on East Asian summer precipitation and 500 hPa height field:the Pacific SST index with the East Asian summer precipitation and 500 hPa height field have good corresponding relation, so the northern Pacific SST and the western Pacific SST is one of the important causes of interdecadal changes to East Asian summer precipitation and 500 hPa height field.(3) The decadal variability of summer integrated water vapor transport, which is caused by the change of zonal water vapor, is similar to that of precipitation over the northern part of East Asia in the late 1990s. Moreover, the decadal change is more significant along the western boundary than the eastern boundary. In terms of SST, there is a significant correlation between previous winter North Atlantic SST and summer 500 hPa height field,850 hPa wind field and specific humidity. In the late 1990, SST changes from cool to warm in winter and the warm anomaly persists into the following summer. The summer North Atlantic SST anomaly generates an Atlantic-Eurasia (AEA) teleconnection structure on the corresponding period which is across the North Atlantic and the middle-high latitude of Eurasia, and further influences the summer water vapor transport over the northern part of East Asia.