我国华北地区春季降水的年代际变化特征及其可能成因的探讨

Characteristics of Interdecadal Variability of Spring Precipitation in North China and Its Possible Cause

利用我国160个台站1951-2000年逐月和华北地区80个台站逐日降水观测资料，分析了我国，特别是华北地区春季降水的年代际变化特征。分析结果表明：华北地区春季降水具有明显的年代际变化，1951～1965年华北地区春季降水略偏少，1966-1976年华北地区春季降水更加偏少，春旱较严重，1977～2000年为华北春季降水明显偏多，这时期5～6月降水比1966-1976年有明显增多；并且，分析结果也表明了华北地区和黄河流域春季降水存在着与夏季降水相反的年代际变化特征。另外，作者还利用欧洲中心ERA40资料集的1958-2000年月平均700hPa风场再分析资料，分析了东亚上空春季700hPa风场的年代际异常情况，从而来探讨华北地区春季降水年代际变化的成因。其分析结果表明：1965年以前，蒙古高原上空存在着明显的反气旋距平环流，我国华北地区有偏北风距平，这使得我国华北地区在1965年以前春季降水偏少；1966-1976年，我国华北地区仍为偏北风距平，且我国东部沿海到南海上空的偏北风距平增强，这使得华北地区春季降水进一步减少；1977-2000年，东亚上空700hPa环流场发生了一个明显的变化，华北地区出现偏南风距平，且我国东部沿海到南海上空的偏南风距平增强，这使得我国南方暖湿气流易输送到华北地区，从而造成我国华北地区春季降水增加。

The characteristics of the interdecadal variability of spring （MAM） precipitation in China, especially in North China, are analyzed by using the observed data at 160 observational stations of China and 80 observational stations in North China during 1951—2000, The analyzed results show that the spring rainfall＇s variability in North China have an obvious interdecadal variability and the variation can be divided into three stages interdecadal timescale from 1951 to 2000. The period of 1951—1965 was a period of below normal of spring rainfall in North China. And during the period of 1966—1976, spring rainfall was still below normal, and it obviously decreased and droughts were severe in spring. However, the period of 1977—2000 was a period of above normal of spring rainfall in North China, especially, the rainfall was more obvious in May and June of this period than that in the period of 1966—1976. Moreover, there was an opposite interdecadal variability between spring and summer precipitation. In order to explain the cause of the interdecadal variability of spring rainfall in North China, the inteMecadal variability of the East Asian circulation anomaly in spring is analyzed by using the monthly mean wind field at 700 hPa of the ERA 40 reanalysis data of ECMWF during 1958—2000. The analyzed results show that there was an obvious anticyclonic anomaly circulation over the Mongolian Plateau and the northerly wind anomaly distribution over North Chi- na before 1965, which caused below normal of rainfall in spring in this region. Moreover, the anomalies of northerly wind were still strong and the northerly wind anomalies were intensified over the eastern part of China and the South China Sea in the period of 1966—1976, which caused the further decrease of the spring rainfall in this region. However, up to the period of 1977—2000, an obvious change occurred in the 700 hPa circulation anomaly over East Asia, the southerly wind anomalies appeared over North China and the southerly wind anomalies were intensified over the eastern coast of China. This could cause that the warm and wet air-flow were easily transported from South China into North China, which can cause the increase of spring rainfall in North China.