近60年金沙江流域雨季降水的时空变化及其环流特征

Spatial−Temporal Variation of Rainy Season Precipitation over Jinsha River Basin in Recent 60 Years and the Associated Atmospheric Circulation

基于1961~2021年中国大陆格点化降水数据(CN05.1)分析了金沙江流域雨季(5~10月)降水的时空分布特征,发现金沙江流域上游南部、中游以及流域下游的南部(A区),雨季总降水量存在减少趋势,流域上游中部和下游的西北部地区(C区)雨季降水有显著增加趋势,而流域上游的北部(B区)雨季降水的长期变化趋势并不明显,表明流域不同分区在雨季降水长期变化趋势上存在显著的不同。在年际变化尺度上,1961~2012年期间A区与C区雨季降水变化存在显著正相关,呈同位相变化;但在2013年以后,A区和C区降水变化趋势呈反位相,且降水趋势变化的差异主要出现在6月。进一步合成分析表明,1961~2012年期间对应于A区和C区的降水偏多年(偏少年),金沙江流域上空对流层中低层为来自西太平洋的气旋性(反气旋)风场异常,而高层为反气旋(气旋性)风场异常,有利于流域大部地区降水异常偏多(偏少)。2013年之后,研究发现在流域上空的对流层中低层,来自孟加拉湾的西南气流在流域南部形成反气旋风场异常,并在流域北部与来自鄂霍茨克海的气旋性风场异常的偏北风辐合;对流层高层为反气旋风场异常,这有利于流域北部降水偏多,而南部降水偏少。

Based on the gridded monthly precipitation data from CN05.1 during 1961−2021,the spatial−temporal characteristics of precipitation anomalies during the rainy season(May to October)over Jinsha River basin and associated atmospheric circulation are analyzed.The results show that the long-term trend of precipitation varies with regions in the basin.Significantly decreasing trend of precipitation can be found in the southern part of upper reaches,middle reaches and southern part of the lower reaches of the basin(region A),and remarkable increasing trend of precipitation can be found in the middle of the upper reaches and the northwestern part of the lower reaches of the basin(region C).Meanwhile,weak and insignificant increasing trend of precipitation can be found in the northernmost part of the upper reaches of the basin(region B).In terms of interannual variation,it is found that precipitation in regions A and C varies in the same phase during 1961−2012,while they are in opposite phase during 2013−2021,which is more prominent for June precipitation.Further composite analysis suggests that,for more(less)June precipitation years,there were cyclonic(anti cyclonic)wind anomalies in the middle and lower troposphere over Jinsha River basin originated from Western Pacific Ocean,while in the upper troposphere there were anticyclonic wind anomalies,which were conducive to excessive precipitation anomalies in the Jinsha River basin.After 2013,in the middle and lower troposphere over the basin,an anomalous anticyclonic wind anomalies in the southern part of the basin can be found,which is originated from the southwest air current from Bay of Bengal,it converged with cyclonic wind anomalous from Okhotsk Sea in the northern part of the basin,and the upper troposphere is controlled by an anomalous anticyclonic circulation,which is conducive to more precipitation in the north of the basin and less precipitation in the south.