青藏高原中东部夏季降水变化及其与北大西洋涛动的联系

VARIATION OF SUMMER RAINFALL OVER QINGHAIXIZANG PLATEAU AND ITS ASSOCIATION WITH THE NORTH ATLANTIC OSCILLATION

中文关键词:  青藏高原  夏季降水  经验正交函数  北大西洋涛动  西风环流

英文关键词:Qinghai-Xizang Plateau  Summer rainfall  EOF  North Atlantic Oscillation  Westerly circulation

中文摘要:

      利用青藏高原中东部地区1961～1990年2000m以上的66个台站夏季(6～8月)降水资料分析了其时空变化特征,发现高原南北降水具有反向变化的特点;结合500hPa高度场及风场资料,讨论了造成高原中东部降水异常的环流特征,指出北大西洋涛动变化可能是影响高原中东部降水的重要原因之一。与北大西洋涛动相联系的中纬度西风异常,通过对高原的西风环流的动力作用的改变,进而引起高原南北槽脊系统的同时加强或减弱,最终造成高原南北部降水的相反变化。

英文摘要:

      By using 1961-1990 summer (June-July-August) rainfall data from 66 stations located at more than 2000m above sea level on the central and eastern Qinghai-Xizang Plateau,the temporal evolutions and spatial structures of the summer rainfall are revealed through the empirical orthogonal function (EOF) analysis. It is found that the dominant spatial pattern of the summer rainfall variation over the Plateau is a seesaw between the southern and northern parts and the temporal variation of the dominant pattern is closely correlated with the North Atlantic Oscillation (NAO).A possible mechanism of the correlation is proposed on basis of statistical analyses with the geo-potential height and wind field data over the Northern Hemisphere. In a summer when the NAO index is low, the westerlies in mid-latitudes from eastern Atlantic to western Europe increases. Enhanced westerlies will bring about a strong flow around the Plateau when passing the Plateau and so the ridge or anticyclonic vorticity in the northern part and the trough or cyclonic vorticity are strengthened simultaneously. In this case, the summer rainfall is usually above the normal in the southern Plateau but below the normal in the northern Plateau. In a summer with a high NAO index, the above processes are opposite.