中国东部夏季降水与同期东亚副热带急流年代际异常的关系  

Relationship between the East Asia Subtropical Westerly Jet Anomaly and Summer Precipitation over Eastern China

作　　者：孙凤华[1] 张耀存[2] 郭兰丽[2] 

机构地区：[1]中国气象局沈阳大气环境研究所,辽宁沈阳110016 [2]南京大学大气科学学院,江苏南京210093

出　　处：《高原气象》2009年第6期1308-1315,共8页Plateau Meteorology

基　　金：国家自然科学基金项目(40675041);财政部/科技部公益类行业专项(GYHY200706005)共同资助

摘　　要：利用中国738个台站的降水观测资料和NCEP/NCAR再分析资料,分析了我国降水和200hPa东亚副热带西风急流轴的年代际变化特征,揭示了东亚副热带西风急流位置的南北移动与我国长江流域和华北降水异常之间的联系。结果表明,我国东部地区夏季(7、8月)降水异常主要表现为长江中下游地区多(少)雨,华北及华南地区少(多)雨,20世纪70年代末80年代初是这种异常分布型发生转折的时间。与此同时,东亚高空副热带急流轴位置从70年代末开始逐渐偏南,急流轴位置的变动将引起对流层低层水汽辐合区和高层散度分布以及垂直环流相应的变化,进而引起降水区域的变化。相关分析发现,当急流位置偏南时,25°～35°N西风增强,42°～50°N西风减弱,华北夏季降水减少,长江中下游地区夏季降水增多;反之,当急流位置偏北时,华北夏季降水增多,长江中下游地区夏季降水减少。与70年代末开始的我国东部地区急流轴位置逐渐南移相对应,华北地区夏季降水呈现逐渐减少、长江中下游地区夏季降水呈现逐渐增多的变化趋势。分析低层水汽通量和高层的散度分布以及垂直环流的差异发现,1980年以来华北地区对流层中低层水汽通量辐合减弱,水汽供应减少,垂直上升运动减弱,造成了华北夏季降水减少,而长江中下游地区水汽通量辐合增加,水汽供应增多,垂直上升运动增强,导致该地区降水增加。Interdecadal changes of the East Asia subtropical westerly jet （EASWJ） and the precipitation in July and August （JA） are examined by using the observational data at 738 stations and the NCEP/ NCAR reanalysis. The relationship between the location displacement of EASWJ and the precipitation anomalies over North China and the Yangtze River valley are also investigated. The results show that an anomaly pattern with more （or less） precipitation along the Yangtze River valley and less （or more） precipitation over North and South China occurs in eastern China, and this pattern changes at the end of 1970s. At the same time, the axis location of EASWJ displaces southward from the end of 1970s, leading to changes in water flux convergence in the lower troposphere and divergence in the upper troposphere and vertical circulation, as a result, precipitation anomaly pattern changes. Correlation analysis indicates that while the jet axis is abnormally southward, the westerly wind over the region of 25°-35°N intensifies, weakens over the region of 42°-50°N, and the precipitation in North China decreases and increases along the Yangtze river valley, and vice versa. With the southward displacement of the EASWJ axis from the end of 1970s, a trend of increase and decrease in summer precipitation over North China and the Yangtze River valley occurs. Comparisons of the differences of the water vapor flux convergence in the lower troposphere, divergence in the upper troposphere and the vertical circulation show that the water vapor flux convergence in the lower troposphere weakens from 1980s, water vapor supply decreases, vertical motion suppressed, leading to a decrease in the precipitation over the North China, and vice versa along the Yangtze River valley.

关 键 词：中国东部降水 夏季 东亚西风急流 年代际异常 

分 类 号：P434[天文地球—大气科学及气象学]