近30年江淮流域夏季年代际干旱特征及其与欧亚西风环流异常的关系

Decadal Summer Drought Characteristics over Yangtze-Huaihe River Basin in Recent 30 Years Associated with Abnormal Eurasian Westerly Circulation

由于在夏季影响中国江淮流域降水的主要行星尺度系统在7月中旬发生改变,因此利用中国北方501个观测站点降水资料、ECM WF再分析资料及NOAA海温数据分析了6月1日至7月15日(梅雨期)和7月16日至8月31日(伏旱期)两个时段江淮流域干旱的时空特征和年代际极端干旱年份时的大气环流异常特征及其可能原因。结果表明,江淮流域在夏季梅雨期和伏旱期两个时段里均有变干趋势;梅雨期200 h Pa东欧关键区的能量向东频散,激发出欧亚型(EU)波列,在我国北方辐合,促使江淮流域上空反气旋式异常环流加强,有利于该地干旱的维持和发展。伏旱期200 h Pa高度上北大西洋关键区波能沿EU路径东传,叠加我国北方来自下垫面强迫的能量后在高空辐散,使蒙古上空低压槽减弱,同样有利于干旱的维持;该结果反映了江淮流域干旱的年代际特征及其部分成因,为多尺度干旱机理的探讨及干旱气候预估提供依据。

As the main planetary system affecting the precipitation over Yangtze-Huaihe river basin in summer changed in mid-July,this paper investigated the temporal and spatial characteristics of arid in Yangtze-Huaihe river basin and the characteristics of atmospheric abnormal circulation in interdecadal extreme drought years and their possible causes from June 1 to July 15（Meiyu period） and July 16 to August 31（drought period）.This research based on daily precipitation data from 501 stations in northern China,the reanalyze data from European Centre for Medium-Range Weather Forecasts（ECMWF） and the sea temperature data from national oceanic and atmospheric administration（NOAA）.The results indicate that on the spatial scale,the number of rainless day in the northwest of the Yangtze-Huaihe river basin in the Meiyu period is more than that in the southeast,while there is no significant difference in the number of rainless day in the entire Yangtze-Huaihe river basin during the drought period.On the time scale,the drought in the Jianghuai basin was more severe than in other periods at the end of the 20 th century,and there were dry trends during the two periods.The drought in the Yangtze-Huaihe river basin is related to the Eurasian teleconnection in the middle and high latitudes.During the Meiyu period,there is a northeast-southwest anticyclone anomaly in Mongolia with a strong intensity range.Therefore,the Yangtze-Huaihe river basin is affected by the northerly wind and the subsidence movement is maintained,providing a circulation background that is easy to form a drought in this region.During the drought period,there is a positive anomaly at 500 hPa over the eastern Mongolia,which weakens the East Asian trough and causes the west Pacific subtropical high to move northward.This area is controlled by descending airstream,resulting in aridity.In the Meiyu period the 200 hPa wave energy from Eastern Europe propagates eastward and converges in the north of China,which intensifies abnormal anticyclone.Such phenomenon is conducive to the maintenance and development of drought in the Yangtze-Huaihe river basin.During drought period,the 200 hPa origins of wave energy are the North Atlantic and the north of China.Wave energy from North Atlantic propagates eastward,with a small amount transported to East Asia.In the northern China the energy diverges after combining with energy wave forced by surface.The weakened trough in Mongolia leads to the formation of anti-cyclonic abnormal center,which is conducive to the maintenance of drought.The results present the interdecadal characteristics and factors of drought in the Yangtze-Huaihe river basin to some extent,and provide the basis for the study of multiscale drought mechanism and arid climate prediction.