中国西北地区春末夏初降水异常的时空变化特征

THE FEATURE OF THE SOILTEMPERATURE GRADIENT OVER CHINAAND ITS APPLICATION IN PREDICTINGSUMMER RAINFALL

利用中国西北五省（区）９０个测站１９６０～１９９０年历年５～６月月总降水量资料，采用ＥＯＦ和ＲＥＯＦ方法对春末夏初降水的空间异常特征、时间变化规律以及降水异常的主要成因进行了诊断研究。结果表明：中国西北地区春末夏初降水的主要空间异常型表现为全区一致的多雨或少雨型；南北相反变化型和东西相反变化型。西北地区春末夏初降水的主要异常敏感区为西北东部区、河西走廊区、青藏高原东侧区、北疆区、江河源头区和沙漠盆地区。５０年代以来，西北东部，北疆和江河源头地区的降水量经历了多雨—少雨—多雨的抛物线过程，而河西走廊、青藏高原东侧及沙漠盆地降水量呈总体上升趋势。从环流形势看，当５月北半球５００ｈＰａ高度距平场结构呈现出明显的正ＰＮＡ型和负ＥＵ型时，同期中国西北地区降水偏少。春季青藏高原地面加热场的增强有利于西北地区降水偏多。

First,it has been made that the climatological analysis of January's monthly nean 1.6～0.8m soil temperature vertical gradient field of the middle and eastern China. The results of Empirical Orthogonal Function(EOF) decomposition show that the field of the soil temperature vertical gradient departure of the middle and eastern China has meso-scale and macro-scale characteristics. Based on the climatological analysis, we use the methods of composite analysis, correlation analysis and Singular Value Decompsition(SVD) to study the relationship between soil temperature vertical gradient and general circulation of the northern hemisphere. We obtained the finding that the mutual contribution between the anomalies of the soil temperature vertical gradient and general circulation evidently exists in the same month. Through investigating coherence between the field of 1.6～0.8m soil temperature vertical gradient and the flood period precipitation in the eastern China, we make the forecasting of the eastern China in the flood period with the field of 1.6～0.8m soil temperature vertical gradient departure, the fitting of 30 years (1955～1984) and the prediction of independent sample(1985～1988). From the result of forecast, we can find that the method, which forecast the precipitation of flood periods with the field of the soil temperature vertical gradient, is effective.