西北地区夏季降水异常的时空特征分析

ANALYSIS OF SUMMER PRECIPTITION TIME AND SPATIAL FEATURES IN NORTHWEST CHINA

本文使用西北地区95个测站,时间序列为1960—2000年共41年的加密测站资料,运用旋转经验正交函数分解（REOF）以及功率谱分析等方法,对西北地区夏季降水的时空特征及其演变规律进行了诊断分析。结果表明,西北地区夏季降水区域性较强,存在多时空尺度特征,且平均具有准3年和4.8年的周期变化。将西地区夏季水异常区域划分为4个区后可见,北疆地区夏季降水的周期振荡最接近平均状况,南疆降水异常区次之,相比之下青海异常降水区解释方差最小。同时发现,在近41年来,西北地区夏季降水的平均状况是80年代以前多数年份降水偏少,干旱性强,80年代以后整个西北地区夏季降水则有增多的趋势;分区分析后表现为:北疆区和南疆区从80年代后期开始降水增多,内蒙古西部地区90年代以后降水增多,而东北高原区夏季除70年代到80年代中期降水偏多外,其前和其后降水都偏少。

With the help of REOF and spectral analysis, the summer rainfall spatial anomaly feature and time evolution rule in Northwest China are studied on the basis of the precipitation data in summer for the period 1960-2000 collected from 95 observational stations. The result is that the summer rainfall in Northwest China has distinct territorial and multi-time scale features,and has the periods of quasi-3 and 4. 8 years oscillations. After dividing the abnormal summer rainfall regions of Northwest China into four subareas,we can see that the summer rainfall oscillation of north Xinjiang is the closest to the average,and then is south Xinjiang, the explained variance of abnormal summer rainfall in north ?east Qinghai-Tibet Plateau is the least. In the recent 41 years the summer rainfall in Northwest China is little in most years before 1979 and has a rising trend after the 1980's. It shows that the summer rainfall rises from the end of 1980's in the neighborhood of north and south Xinjiang and from the 1990's near western Mongulia. The summer rainfall hereabout north-east Qinghai-Tibet Plateau tends to be less in every year except time from the 1970's to the latter of 1980's.