瞬变天气涡旋对北大西洋涛动的增强效应  

Enhancement of North Atlantic Oscillation by Transient Eddies

作　　者：张冬斌[1,2,3] 金飞飞[4] 李建平[1] 丁瑞强[1] 

机构地区：[1]中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室,北京100029 [2]国家气象信息中心,北京100081 [3]中国科学院研究生院,北京100049 [4]夏威夷大学气象系

出　　处：《大气科学》2011年第5期927-937,共11页Chinese Journal of Atmospheric Sciences

基　　金：国家重点基础研究发展规划项目2010CB950400;国家自然科学基金资助项目41030961;40805022

摘　　要：使用NCEP/NCAR再分析资料计算了冬季北大西洋瞬变涡旋活动强度与北大西洋涛动(NAO)逐日指数的时间序列,结果发现:当涡旋活动强度出现峰值后会伴随NAO模态增强现象;而随着NAO的增强,涡旋能量回落。为了判断是否涡流相互作用将天气尺度的能量转换为低频尺度的能量,使用瞬变涡度通量来研究涡度与能量的传输。通过分析瞬变涡旋与低频环流随时间的演变,发现瞬变涡旋可以激发出低频异常,其对涡度的输送可以加强低频异常,使得NAO指数增强。由于涡旋与低频流以及涡度通量均随时间变化,不一定总能达到平衡,因此从方程稳定性解的角度来分析在足够长的时段各种随机涡旋对于激发类似NAO模态的响应所起到的综合作用,结果显示瞬变涡旋使得稳定性解更接近于NAO模态。Time series of the intensity of North Atlantic transient eddy activity and a daily index of the North Atlantic Oscillation（NAO） are calculated by using the NCEP/NCAR reanalysis data.The results suggest that peaks in the intensity of eddy activity are followed by strengthening of the NAO mode,accompanied by a collapse in eddy energy.To determine whether the interaction between eddies and low-frequency flow results in the transformation of synoptic-scale energy to low-frequency-scale energy,the eddy vorticity flux is used to investigate the transfer of vorticity and energy.The results show that transient eddies can induce low-frequency anomalies and that vorticity transfer can enhance the anomaly,resulting in an increase in the NAO index.However,eddies,low-frequency flow,and the vorticity flux show continuous variations,meaning that they cannot attain equilibrium all the time.Accordingly,the authors analyze the total contribution of stochastic eddies to the process that induces an NAO-like response to external forcing.The steady solution suggests that eddy forcing can induce a response more similar to the NAO mode.

关 键 词：瞬变天气涡旋 北大西洋涛动 瞬变涡度通量 

分 类 号：P461[天文地球—大气科学及气象学]