西北地区东部夏季降水日数的变化趋势及其气候特征

Climate characteristics of summer precipitation days in eastern part of northwest

以西北地区东部(95°E～112°E,32°N～41°N)104个测站1960～2000历年夏季(6～8月)降水日数资料为基础,通过EOF和REOF等分析方法,研究夏季降水日数时空分布的异常特征。结果表明西北地区东部夏季多年平均降水日数的地区分布特点是西部多、东部少,沿祁连山山脉存在一个降水日数较多中心区域,并且降水量和降水日数均呈增多趋势。降水日数的空间异常主要表现为一致性异常和南北相反异常两种类型。根据REOF方法可将西北区东部分为5个不同降水日数气候区,即甘肃中东部及河套区、渭水流域区、河西走廊区、青海高原北部区、青海南部区和四川北部区。20世纪80年代以来,西北地区东部大部分地区降水日数呈现减少的趋势。冬季(或夏季)青藏高原地面加热场强度偏强,甘肃河西及祁连山地区、宁夏南部等地夏季降水偏多(或少),青海东南部-甘肃南部-渭水流域夏季降水日数偏少(或偏多)。

Using the observed data at 104 stations in the eastern part of northwest China during 1960-2000, spatial and temporal abnormity characteristics of summer precipitation days were analyzed by the means of EOF and REOF. The results showed that the summer precipitation days is more in the west regions than the east regions, and a precipitation center lies along Qilian mountain, where the days and amount of precipitation are higher. There are two types of spatial abnormity distribution: consistent abnormity and north-south reverse abnormity. The climate region can be divided into 5 sections, i.e., the middle-east part and Hetao of Gansu, Weihe river basin, Hexi Corridor, northern Qinghai, southern Qinghai and northern Sichuan. In 1980's the precipitation days decreased gradually. The summer precipitation days is influenced by the intensity of surface heat-field in Qing-Zang Plateau in winter and summer.