1980-2010年冬季北极涛动季节内振荡的成因分析

Cause analysis of AO intraseasonal oscillation in winter of 1980—2010

采用NCEP/NCAR日平均再分析资料,对冬季热带外低频振荡（大气角动量收支及地形力矩）与AO（Arctic Oscillation）指数进行计算,通过功率谱和统计分析发现,它们都存在30~60 d的周期,大气角动量收支与山脉力矩的变化为正相关,且显著响应AO变化。通过动力学诊断分析初步认为,北半球两大地形的山脉力矩作用于纬向大气角动量,副热带纬向西风发生变化,改变南北西风偶极子结构,使得AO产生变化,而且在两大地形中以喜马拉雅山脉地形作用为主。通过对喜马拉雅山脉地区的动力学诊断发现,在高（低）AO指数阶段,喜马拉雅山脉地区激发准定常行星波并作用于副热带西风,导致副热带西风偏弱（偏强）,高纬西风偏强（偏弱）,因而AO偏强（偏弱）,平流层极涡偏强（偏弱）,极涡强（弱）中心偏向东北亚。

Based on the daily NCEP / NCAR reanalysis data,this paper analyzes the extra-tropical low-frequency oscillation（ atmospheric angular momentum budget and mountain torque） and AO（ Atlantic Oscillation） indices in winter.Pow er spectrum analysis and correlation analysis show that the dominant variations of them occur in 30—60 d band,and the variation of atmospheric angular momentum budget has positive correlation w ith the variation of mountain torque and also responds to the variation of AO significantly. Dynamic diagnostic analysis show s that the mountain torque of the tw o major NH mountain ranges influences zonal atmospheric angular momentum（ zonal w esterly）,and the subtropical w esterly and the north-south w esterly dipole structure change,so the strength of AO changes. In comparison w ith the Rockies,the Himalayas play a important role in AO variation. The dynamic diagnosis of the Himalayas ranges show s that,during the period of high（ low） AO indices,the quasi-stationary planetary w aves forced by the Himalayas ranges influence subtropical w esterly,and the subtropical w esterly w eakens（ strengthens） and the high-latitude w esterly strengthens（ w eakens）,so AO strengthens（ w eakens） and the polar vortex in the stratosphere strengthens（ w eakens）. The strong（ w eak） center of polar vortex tends to Northeast Asia.