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通过调查40年东亚地区500hPa平均位势高度场，结果显示东亚夏季高度场发生明显增高，增高主要发生在4-10月和120°E以西的亚欧大陆上，夏季西太平洋副热带高压明显西伸，夏季东亚大槽至少向西移动20个经度，这可能使我国西北降水增加而华北降水减少。另外印度半岛孟加拉湾高度场也有年代际增高趋势。通过公式诊断半球尺度的“极地-赤道”温度梯度减小和东亚大陆尺度的东西温度梯度减小是共同促使这次东亚大槽年代际西移和副热带高压北扩的主要原因。“,”The 500 hPa potential height field over East Asia has been investigated. Then outcome shows that averaged 500hPa height increased obviously in the past 40 years in this continent. The increase mainly takes place from April to October and mainly over Eurasia continent of west region less than 120°E. West ridge point of Sub- tropical High over west-north Pacific shifts obviously westward in this period, East Asia Trough displaces at least westward by 20 longitude contemporarily. Therefore, the total precipitation over North China possibly decreases, whereas that of Northwest China possibly increases in the wake of variation happening. In addition, the 500 hPa po- tential height field over Indian peninsula and Bay of Bangladeshalso increase simultaneously also. It is diagnosed through the formulas that those possible chief causes of westward displacement for East Asia Trough as well as for northward expansion of Subtropical High are continent-scale longitudinal Temperature Gradient decreases and the reduction in Equator-Pole Temperature Gradient at hemisphere-scale, respectively.