甘肃河东春末夏初干旱的时空特征和预测研究

利用甘肃５５ 个测站，１９６８ ～１９９７ 年５ 月中旬至６ 月中旬降水资料，采用 Ｅ Ｏ Ｆ、 Ｒ Ｅ Ｏ Ｆ、波谱分析，对春末夏初降水异常的空间结构及时间演变特征作了研究。结果表明，甘肃河东春末夏初降水异常在空间上主要表现为陇东、中部、陇东南、甘南４ 个主要类型。河东各主要气候区春末夏初降水的时间变化基本趋势是：８０ 年代春末夏初降水增加，而９０ 年代以来，降水均有不同程度减少，干旱加剧。甘肃河东春末夏初降水变化以短周期振荡为其主要特征。在１０ 年的年际变化中，陇东比各型均落后１ ～２ 年。从环流形势看，当春末夏初北半球５００ｈ Ｐａ 高度距平场结构呈现出明显的正 Ｐ Ｎ Ａ 型时，中国西北地区同期降水偏少

The Spatial and Temporal Features for Drought Variation During Late Spring - Early Summer in the East of the Yellow River in Gansu and its Prediction

The precipitation data at 55 observational stations from 1968 to 1997 are used to analyse the spatial anomaly features and time evolution rule in May and June in EYRGP by EOF,REOF and wave spectrum analysis methods.The results show that the spatial anomaly of late spring -early summer's precipitation in EYRGP can be divided into 4 patterns,i.e,the eastern Gansu(EG),the central Gansu(CG),the southeast Gansu(SEG),and Gannan region.A general increase in late spring -early summer's precipitation was found in each region in 1980s,while an apposed(decrease in precipitation)was discovered in different degrees since 1990s . The drought began to increasingly intensified. The EYRGP'S rainfall variation in late spring -early summer is characterized by short term fluctuation. The EG pattern is usually in lag of 1-2 years,comparising with the rest patterns on decadal time scale.In the aspect of the atmospheric circulation,when the structures of 500hPa geopotential height departure field emerges evident positive PNA ,the rainfall is bellow the average over Northwest China at the sametime .