西印度洋大气垂直环流与江淮夏季降水关系的年代际变化

THE INTERDECADAL VARIATION OF RELATIONSHIP BETWEEN VERTICAL CIRCULATION OVER WESTERN INDIAN OCEAN AND SUMMER RAINFALL IN YANGTZ-HUAIHE VALLEY

利用1958—2013年NCEP/NCAR逐月再分析资料和国家气候中心整编的160站月降水资料,研究了西印度洋大气垂直环流(WIOVC)与江淮夏季降水关系年代际变化的原因。结果表明:两者关系的年代际变化经历了两次转折,1950年代末期的不显著关系在1970年代末转为显著负相关,又在1990年代中后期变为显著正相关。进一步研究发现,两者关系的年代际变化是由WIOVC的年际异常和热带背景场的年代际变化共同作用造成的。在:1980年代以前热带东太平洋大气异常偏强的下沉运动背景下对应东亚夏季风偏强,WIOVC与江淮夏季降水关系不明显。1980年代—1990年代中期,热带东太平洋大气异常偏强的上升运动背景对应东亚夏季风偏弱,WIOVC与江淮夏季降水呈显著反相关。1990年代中期以后,热带东太平洋大气仍为异常上升运动,且热带中太平洋为异常下沉运动,对应东亚夏季风进一步减弱,WIOVC与江淮夏季降水呈显著正相关。

Based on the NCEP/NCAR reanalysis data from 1958 to 2013 and monthly precipitation data from 160 stations compiled by China National Center of Climate, the interdecadal variation of the relationship between the vertical circulation over Western Indian Ocean（WIOVC） and summer rainfall in Yangtz-Huaihe valley is investigated. Results show that this interdecadal variation has experienced two shifts; it was insignificantly negative at the end of 1950s but became significantly negative at the end of 1970s, and it changed to be significantly positive during the middle and late 1990s. It is known from further study that the interdecadal variation is jointly caused by interannual anomalies of WIOVC and interdecadal variation of tropical background field. Before the 1980s, WIOVC coupled with the vertical circulation over tropical East Pacific Ocean. After the 1980s, West Indian Ocean coupled with mid-Pacific Ocean. Among them, in the middle of the 1980s and 1990s, the tropical Eastern Pacific atmosphere had an unusually strong upward movement corresponding to a weakening East Asian summer monsoon; a rain belt was located in Yangtz-Huaihe valley. WIOVC caused the rain belt to shift northward. As a result, WIOVC has a significantly negative correlation with summer rainfall in Yangtz-Huaihe val- ley. After the 1990s, the background presents descending motion over the tropical mid-Pacific Ocean and ascending motion over tropical East Pacific Ocean, with a further weakened East summer monsoon in the north of the Yangtze River and a rain belt located in south China. At this stage, the effect of WIOVC is conductive to rainfall in Yangtz-Huaihe valley with obviously positive correlation.