华北汛期大尺度降水条件的年代际变化
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作者单位
刘海文,丁一汇  
基金项目:国家自然科学基金资助项目(40805026;40975058);成都信息工程学院科研基金资助项目(KYTZ201012);山西省科技厅攻关项目(20100311131)
中文摘要:利用中国740站逐日降水资料和NCEP/NCAR逐日再分析资料,使用合成分析等方法,分析了华北汛期大尺度降水条件的年代际变化。结果表明:以1978年为界,华北汛期异常水汽先由南边界和西边界供应,后改变为由北边界和东边界供应;水汽收支由异常辐合和盈余,改变为辐散和亏损;先前能够到达华北北部甚至接近华北最北边界的暖湿气团,改变为后来只能抵达黄河南岸;并且沿着太行山走向的冷暖空气的相互作用也由强变弱;华北上空由异常上升运动,改变为异常下沉运动;区域平均的对流层涡度的垂直分布,由先前的两层结构(低层正涡度、高层负涡度)改变为后来的三层结构(对流层中低层负涡度、中高层正涡度和高层负涡度),整层涡度效应值也由大变小。尽管华北区域平均的散度和垂直速度,在垂直方向上的结构没有发生明显的年代际变化,但是整层散度效应值和垂直速度值均由大变小。
中文关键词:华北降水  大尺度降水条件  年代际变化
 
Interdecadal variability of large scale precipitation conditions over North China during rainy seasons
Abstract:Based on the daily precipitation data from 740 stations in China and NCEP/NCAR daily reanalysis datasets,the interdecadal variability of large scale precipitation conditions over North China during rainy seasons is analyzed by means of composite analysis methods.The results show that:with a turning point from flood period to dry period in 1978,anomalous moisture budget over North China changed from south boundary and west boundary to north boundary and east boundary and thus made water vapor become divergent and absent from convergent and abundant.Warm and moisture air mass from ocean could reach the north area of North China or even its northern border before 1978,but it could only reach the south bank after 1978.The interaction between the cold and warm moisture air mass along the Taihang Mountain became weaker.In addition,anomalous upward motion became anomalous downward motion over the North China;areal average vorticity changed from two layers structure(positive vorticity in the low levels and negative vorticity in the high levels) to three layers structure(negative vorticity in the middle and lower troposphere,positive vorticity in the middle and negative vorticity in up troposphere) and the value of total vorticity became smaller.Vertical configurations of areal average divergence and vertical velocity presented no conspicuous interdecadal variability,but their values all became smaller.
keywords:North China  large scale precipitation conditions  interdecadal variability
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