近30a来北半球对流层大气月均环流的涡动减弱现象

利用1980-2009年NCEP／NCAR月平均再分析资料，研究了在全球变暖背景下北半球对流层大气涡动减弱现象。结果表明：北半球涡度拟能30a来整体呈减弱趋势，在北太平洋地区和极地减弱尤为显著，12．5～50°N为影响北半球大气涡动变化的关键区域。由于对流层200hPa以下大气的增暖，特别是中高纬地区显著增暖，减弱了经向温度梯度，使得副热带西风急流的强度亦呈减弱趋势。这与涡度拟能的变化有显著的正相关关系。分析了北半球正压Rossby波动诊断量E和热量经向涡动通量的变化，表明中纬度波能传播在不同地区有不同趋势，而热量的经向涡动输送与涡度拟能的变化也呈现显著的正相关关系，减弱明显。研究结果对深刻认识大气环流变化规律和理解全球变暖的可能影响具有重要意义。

Weakening trends of tropospheric enstrophy of monthly mean circulation in the Northern Hemisphere in the past three decades

Using the NCEP/NCAR monthly mean reanalysis data from 1980 to 2009, this paper investi gates the weakening trends of enstrophy in troposphere of Northern Hemisphere under background of global warming. Results show that the enstrophy has a weakening trend in the Northern Hemisphere from 1980 to 2009 ,especially in the North Pacific and polar regions. The zone of 12.550~N is the key area of enstrophy change in the Northen Hemiphere. Changes of the subtropical westerly jet in asso ciation with the meridional gradient of air temperature show that the jet intensity has a weakening trend, which is in accordance with the enstrophy change. A vector E is employed to diagnose the Rossby wave propagations in the atmosphere, showing that the disturbances in the atmosphere elongate more meridio nal in the Northern Hemisphere except western Europe. The meridional eddy heat fluxes in the Northen Hemiphere have also been weakening in the past 30 years. These results are helpful for our better under standing the circulation changes and the influences of global warning.