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北半球定常波输送西风动量的气候态及其年变化
引用本文:王林,陈文,黄荣辉,等.北半球定常波输送西风动量的气候态及其年变化[J].大气科学,2007,31(3):377-388.
作者姓名:王林  陈文  黄荣辉  
作者单位:1.中国科学院大气物理研究所季风系统研究中心,北京, 100080;中国科学院研究生院,北京,100049
基金项目:国家自然科学基金 , 国家重点基础研究发展计划(973计划)
摘    要:利用高分辨率的再分析资料ERA40,分析了纬向平均状态下北半球不同尺度的定常波对西风动量沿经向输送的气候态及其年变化。结果表明,对流层中定常波对西风动量输送最强的区域位于中纬度对流层的中上层,定常波在该区域长年向北输送纬向动量,且输送中心随季节有南北移动和强弱变化。此外,在高纬度地区的对流层中上层以及赤道对流层顶附近还有两个相对较弱的输送中心。前者对西风动量的输送长年向南,其垂直范围从对流层低层一直伸展到平流层下层,中心位置相对固定,强度有明显的季节变化。后者位置也相对固定,但输送方向随季节改变。平流层中定常波对西风动量的输送主要位于中高纬度的平流层中上层,定常波在该区域长年向北输送西风动量,中心位置非常稳定,而强度则随季节变化明显。行星尺度定常波的输送作用与总波动的输送作用非常一致,并在很大程度上决定了波动对动量输送强度的季节变化。天气尺度定常波和10波以上的短波的输送作用主要集中在中纬度对流层的中高层。前者与行星尺度定常波共同决定了该区域内的输送强度,并主导了输送中心的南北移动;后者的作用很小,除夏季外均可以忽略。作者给出的不同尺度定常波对西风动量输送的气候态分布不但可以作为日后研究其年际变化的基础,而且还可以为大气环流模式对大气环流模拟能力的评估提供重要的参考。

关 键 词:定常波  动量输送  气候态  年变化
文章编号:1006-9895(2007)03-0377-12
修稿时间:2005-12-122006-03-06

The Climatology and Annual Cycle of Meridional Transport of Westerly Momentum by Stationary Waves in the Northern Hemisphere
WANG Lin,CHEN Wen,HUANG Rong-Hui and et al.The Climatology and Annual Cycle of Meridional Transport of Westerly Momentum by Stationary Waves in the Northern Hemisphere[J].Chinese Journal of Atmospheric Sciences,2007,31(3):377-388.
Authors:WANG Lin  CHEN Wen  HUANG Rong-Hui and
Abstract:The climatology and annual cycle of zonally averaged meridional transport of westerly momentum by stationary waves(also called the eddy momentum flux) in the Northern Hemisphere are presented and analyzed using European Centre for Medium-Range Weather Forecasts(ECMWF) reanalysis(ERA40) data.Here waves are defined as the departure from zonal means.The Fourier expansion method is adopted to isolate different zonal wave numbers.The climatology of eddy momentum flux by total stationary waves,planetary-scale stationary waves,synoptic-scale stationary waves and short waves is analyzed for four seasons,respectively.The annual cycle of eddy momentum flux is also analyzed in two selected pressure levels(250 hPa and 5 hPa).The result shows that in the troposphere,the most significant flux center,whose transport direction is always towards the North Pole,lies in the upper troposphere at mid-latitudes all the year round,and its intensity and position vary with seasons.Besides this flux center,there are other two flux centers in the troposphere,with one in the mid-troposphere at high latitudes and the other in the tropical tropopause level.In the former center,which extends from the lower troposphere to the lower stratosphere,the transport direction is always towards the south.The position of this center is relatively fixed although its intensity varies obviously with seasons.The position of the latter center also changes little with time;however,the direction of eddy momentum flux in this area varies with time: it is towards the south in winter and towards the north in summer.In the stratosphere there is only one significant flux center in the upper stratosphere at middle and high latitudes.In this center the momentum transport by waves is always towards the north.The position of this center changes little with time;the transport intensity in this area varies with seasons: it is the strongest in winter,weaker in autumn,much weaker in spring and nearly zero in summer.The planetary-scale stationary waves(zonal wave numbers 13) play a crucial role in the process of eddy momentum transport and dominate the intensity variation of momentum transport.They lead to the intensity variation in the upper troposphere at mid-latitudes and dominate the intensity and position of the rest three flux centers.The synoptic-scale stationary waves(zonal wave numbers 49) mainly transport westerly momentum in the upper troposphere at mid-latitudes;they dominate the north-south movement of the flux center in this area.Moreover,they,together with the planetary-scale stationary waves,determine the transport intensity in the troposphere at mid-latitudes.Short waves,whose wave number is larger than ten,mainly transport westerly momentum in the upper troposphere at mid-latitudes.The eddy momentum flux produced by short waves is about half of that produced by stationary waves in summer.Hence,the transport effect by short waves should be considered in summer and is negligible in other seasons.The climatology and annual cycle of zonally averaged meridional transport of westerly momentum by stationary waves presented in this paper is not only a basis for further research on their interannual variability,but also an important reference for the GCM simulations.
Keywords:stationary waves  meridional transport of westerly momentum  climatology  annual cycle
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