夏季北极涛动与西北夏季干湿特征的年代际关系

Inter-decadal Relationships between Summer Arctic Oscillation and Aridity-Wetness Feature in Northwest China

利用中国西北地区(新、青、甘、宁、陕及内蒙古西部地区)1960—2003年131个测站夏季降水量、小型蒸发皿蒸发量,NECP/NCAR月平均再分析资料及夏季北极涛动指数,首先通过降水量和蒸发量定义了均一化干湿指数,进而分析了夏季北极涛动同西北地区夏季干湿特征之间的关系。研究表明:夏季北极涛动与西北地区大部分地区夏季干湿特征之间存在着显著的正相关关系,特别是年代际尺度上关系尤其密切。夏季北极涛动与西北地区夏季干湿特征空间变化的南北差异密切相关,在夏季AO偏强年代,海平面气压场在东亚大陆为正距平,太平洋为负距平;700hPa风场在贝加尔湖地区及其下方有较强的反气旋性距平环流,西北西风带区出现西风距平,季风区出现北风距平,而500hPa高度场在中国西北地区表现为西低东高结构。这样使得东亚夏季风偏弱,西北西风带区在夏季以西风气流为主,降水偏多,气候偏湿,而季风区盛行偏北气流,降水偏少,气候偏干。反之亦然。

Based on observation data of summer precipitation and evaporation from 1960 to 2003 at 131 stations in Northwest China （Xingjiang, Qinghai, Gansu, Ningxia, Shanxi and the west of Neimenggu） and summer Arctic Oscillation index, at first, an aridity-wetness homogenized index was defined, then the correlation between summer Arctic Oscillation and summer drought and moist characteristics of northwest China was analyzed. The results show that the inter-decadal correlation is prominent between summer Arctic Oscillation and summer drought and moist characteristics of northwest China. In decades with strong summer Arctic Oscillation, the sea level pressure （SLP） was positive anomaly in East Asia and negative anomaly in Pacific; 700 hPa wind field showed anticyclone anomaly circumfluence in Baikal and its south region, west wind anomaly in westerly region of Northwest China and north wind anomaly in monsoon region of Northwest China; 500 hPa height field showed west-low and east-high characteristics in Northwest China, thus the East Asia monsoon was weakened, the west wind air flow prevailed in westerly wind region of Northwest China, precipitation increased and the climate became wetter, while north wind air flow prevailed in monsoon region of Northwest China, precipitation decreased and the climate became more dry, and vice versa.