青藏高原气温的年际变率与大气环状波动模

THE RELATIONSHIP BETWEEN THE INTERANNUAL VARIABILITY OF AIR TEMPERATURE OVER THE TIBETAN PLATEAU AND THE NORTHERN HEMISPHERIC ANNULAR-WAVE PATTERN

基于1961年3月至2002年2月间青藏高原地区64个台站的地面气温观测资料和ERA40再分析数据集,研究了青藏高原上空气温的年际变率及其与大尺度环流的关系。结果表明除夏季外,高原地面气温与整个北半球副热带、极地对流层的温度和位势高度有显著的同位相变化关系,而与中高纬度对流层有显著的反位相变化关系。其中北半球副热带还有5个分别位于青藏高原、西太平洋、北美西部、大西洋中部、北非到阿拉伯半岛的活动中心。这3条环状活动带和5个副热带活动中心共同组成了一种北半球大气环状波动模,其纬向特征为异常偏强的中纬度西风气流以及热带和高纬度东风气流,并伴有中纬度大气长波槽脊的减弱;经向基本特征为异常偏强的Hadley和Ferrel环流以及副热带下沉气流和中纬度上升气流,垂直方向呈相当正压结构。当这种环状波动模处于正位相时,异常增强的绝热下沉增温效应和减弱的冷空气活动共同使得高原上空对流层中、低层气温异常偏暖。

By using 64-station-based surface air temperature over the mid-eastern Tibetan Plateau and the ERA40 Reanalysis data in the period Jan 1961 - Feb 2002, the anomalous large-scale circulation pattern related to the interannual variability of air temperature over the Tibetan Plateau has been investigated. Results show that, except in summer, there is a significant positive correlation between the surface air temperature over the plateau and the Northern Hemispheric subtropical and polar tropospheric air temperature and geopotential height fields. Among the subtropical annular belt, five correlation centers exist over the Tibetan Plateau, west Pacific, northern North America, mid Atlantic, as well as the area from north Africa to Arabia. However, an inversed negative correlation belt can be detected in the mid-high latitudes. Therefore, these three annular activity belts together with the five subtropical activity centers form a kind of Northern Hemispheric annular-wave mode. In zonal direction, it is characterized by abnormally strong tropospheric westerlies in mid- latitudes and easterlies in tropical and high-latitudes, which is accompanied by the weakened long wave troughs and ridges over mid-latitudes. In meridional direction, it is characterized by abnormally strong Hadley and Ferrel cells, which is accom- panied by intensified subtropical descent and mid-latitudes ascent. And this annular-wave mode is also featured by the equivalent-barotropic structure in vertical. When this annular-wave mode in its positive phase, the integrated effect of the weakened cold air intrusion and enhanced adiabatic descent leads to the anomalous warm in the mid-and lower-troposphere over the plateau.