近44 年来青藏高原夏季降水的时空分布特征

利用1961-2004年青藏高原97个站点的夏季逐日降水数据,通过累积距平、相关分析、回归分析、经验正交函数分解、功率谱方法等,结合GIS的空间分析功能,分析了夏季降水的时空分布特征.结果表明:在青藏高原年降水量比较少的地区,夏季降水占全年降水的比例较高,夏季降水与全年降水的相关性也较强;夏季降水相对变率最大的地区位于青藏高原西北的最干旱地区,最小的地区是三江源区;夏季降水趋势增加和减少的站点分别为54个和43个.通过较显著检验的站点占总数的18.6%:在2000m以下的站点中,海拔和夏季降水气候倾向率存在较强的正相关,相关度达0.604(显著性0.01);1961-1983年和1984-2004年两个时间段相比,除了3000～3500 m海拔范围外,其余海拔范围夏季降水气候倾向率都表现为增加;夏季降水可大致分为三种类型场:高原东南部类型场、高原东北部类型场和三江源类型场,高原东南部类型场和高原东北部类型场表现出南北变化相反的降水特点,分界线大致沿着35°N线;在90%的置信概率下,三种类型场分别表现出5.33年、21.33年和2.17年的潜在周期;4500 m以上海拔范围的站点夏季降水周期通过很显著检验(α=0.01),站点海拔和降水周期存在-0.626的高相关度;在三江源地区,3500 m以上的站点夏季降水周期随海拔升高而减小,3500 m以下的夏季降水周期随海拔高度升高而增加.

Temporo-spatial Distribution of Summer Precipitation over Qinghai-Tibet Plateau during the Last 44 Years

The summer day-by-day precipitation data of 97 meteorological sites on the Qinghai-Tibet Plateau from 1961 to 2004 were selected to analyse the temporo-spatial distribution using accumulated variance,correlation analysis,regression analysis,empirical orthogonal function,power spectrum function and spatial analysis tools of GIS. The result showed that summer precipitation occupied a relatively high proportion in the area with less annual precipitation on the Qinghai-Tibet Plateau and the correlation between summer precipitation and annual precipitation was strong. The altitude of these stations or points and summer precipitation slope presented stronger positive correlation below 2000 m,with correlation value up to 0.604 and significance of 0.01. Summer precipitation slopes disparity between the periods 1961-1983 and 1984-2004 at five altitude scopes (2000-2500 m,2500-3000 m,3500-4000 m,4000-4500 m and above 4500 m) were above zero and accounted for 71.4% of the total. Using empirical orthogonal function,summer precipitation could be roughly divided into three precipitation pattern fields: the southeast Plateau pattern field,the northeast Plateau pattern field and the Three Rivers' Headstream Regions pattern field. The former two presented a reverse spatial distribution value from the north to the south and the reversal line is along 35oN. The potential cycles of the three pattern fields were 5.33a,21.33a and 2.17a respectively,tested by the confidence probability of 90%.