| 夏季纬向平均气流变动的主要模态及其与AO和ENSO的联系 |
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| 引用本文： | 白莹莹,管兆勇.夏季纬向平均气流变动的主要模态及其与AO和ENSO的联系[J].气象学报,2007,65(3):372-383. |
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| 作者姓名： | 白莹莹 管兆勇 |
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| 作者单位： | 南京信息工程大学江苏省气象灾害重点实验室,大气科学院,南京,210044 |
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| 摘 要： | 使用NCEP-NCAR月平均再分析资料,研究了夏季纬向平均气流变动的主要模态及其与北极涛动(AO)和ENSO的联系,探讨了夏季u]主要模态维持的可能机制。结果表明,北半球夏季纬向平均u]的异常分布表现为两个主要模态。EOF1反映了与AO相对应的纬向平均u]的分布,EOF2反映了与ENSO相对应的纬向平均u]的分布。周期分析显示了EOF1、EOF2分别具有与AO及ENSO相似的周期。滞后相关分析表明,除了夏季之外的其他季节EOF1与ENSO存在显著相关,而EOF2与AO亦存在显著相关。夏季,EOF1与ENSO、EOF2与AO的同期相关量值小且不显著。这些说明,北半球夏季纬向平均气流变化的主要模态可以有效分离,其分别代表了AO和ENSO有关的信号。这对于更好地理解AO和ENSO的全球影响具有重要意义。利用准地转无加速定理,发现EOF1和EOF2对应的时间系数高低值年的E-P通量散度的合成差值场分别与纬向平均u]的EOF1、EOF2分布表现出很好的对应关系,其中行星波对纬向平均气流主要模态的维持起着主要作用。余差环流与E-P通量散度分布型相似,量值相当,但符号相反。在一些地区,大气涡动的摩擦耗散也起着一定的作用。这些平衡了波动的能量输送作用,使纬向平均u]的结构得以维持。
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| 关 键 词： | 夏季 纬向平均气流 北极涛动 E-P通量 |
| 修稿时间： | 2006年9月26日 |
PRINCIPAL MODES OF SUMMERTIME ZONAL-MEAN FLOW AND THEIR RELATIONS WITH AO AND ENSO |
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| Bai Yingying,Guan Zhaoyong.PRINCIPAL MODES OF SUMMERTIME ZONAL-MEAN FLOW AND THEIR RELATIONS WITH AO AND ENSO[J].Acta Meteorologica Sinica,2007,65(3):372-383. |
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| Authors: | Bai Yingying Guan Zhaoyong |
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| Abstract: | The NCEP/ NCAR reanalysis data have been employed to diagnose variations of the zonal mean flow in boreal summer.Two leading EOF modes are found to dominate the spatial and temporal changes of the summertime zonal-mean zonal winds in the troposphere.The EOF1 mode shows the distribution of zonal-mean flow anomalies with higher variance in the North Polar Region,whereas the EOF2 mode shows the distribution of zonal-mean flow anomalies with higher variance in tropical and extra-tropical regions.The EOF1 and EOF2 have respectively the periodicities similar to those of AO and ENSO.Significant lag correlations have been found between EOF1 and ENSO,and between EOF2 and AO,in the seasons including spring,fall, and winter.However,no significant correlations have been found between EOF1 in summer and ENSO in any other seasons and between EOF2 in summer and AO in other seasons,no matter how long the lag interval is.These results suggest that the principal modes of summertime zonal mean flow could be statistically separated from each other.Hence,EOF1 and EOF2 are physically related to the AO and ENSO,respectively.The quasi-geostrophic non-acceleration theorem has been used to partly explain the possible mechanisms of the maintenance of the two principal modes.The composite difference fields of the divergence of E-P flux between positive and negative years of the time coefficients of EOF1 and EOF2 exhibit the two patterns similar to the EOF1 and EOF2 modes of the zonal-mean zonal wind anomalies,respectively.It is the planetary waves rather than the synoptic waves that dominate the behaviors of the E-P fluxes,suggesting the crucial role of the planetary waves in the maintenance of the zonal mean flow anomalies.The residual circulation basically cancels the divergence of the E-P flux,but in some areas,such as the upper troposphere in the tropics and the low troposphere in the mid-high latitudes,the friction also play an important role.These results are very helpful for us to better understand how does the anomalous zonal mean flow maintain and how do the ENSO and AO influence the global climate variations. |
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| Keywords: | ENSO |
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