On the Northern Annular Mode Surface Signal Associated with Stratospheric Variability

On the Northern Annular Mode Surface Signal Associated with Stratospheric Variability
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与平流层变率相关的北环模表面信号

DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
R. Greatbatch
R. Greatbatch
中科院分区：
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文献类型：
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作者：
T. Kunz;R. Greatbatch

文献摘要

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冬季北方环形模式（NAM）在地面上是已知的经历缓慢的季节内变化与平流层的变化，导致地面信号长达几个星期。然而，潜在的相关平流层对流层耦合机制的相对贡献尚未完全理解。 在这项研究中，相对作用，（一）向下的影响，地带性平均中学 环流引起的准地转（QG）调整平流层波阻和辐射阻尼和（ii）波阻当地对流层，估计。为此目的，QG纬向平均纬向风的谱趋势方程的推导，并使用，在第一步中，获得外部机械强迫，在QG框架，驱动器正好观测到的平流层和对流层每日NAM。在第二步中，然后将该方程在时间上积分以重建每日NAM，但强迫限于平流层或对流层水平，每种情况都留下特征NAM表面信号。 上述机制的相对作用是相似的 数量上的重要性，但在质量上有所不同。平流层QG调整的向下影响是NAM表面信号开始的原因，而随后当地对流层波阻力积极维持并持续数周的信号。 此外，QG调整的平流层辐射阻尼的向下影响被证明只有一个很小的影响，相比，从平流层波阻。这些结论的鲁棒性证明了相对于各种模型参数的敏感性研究。
The wintertime northern annular mode (NAM) at the surface is known to undergo slow intra-seasonal variations in association with stratospheric variability which leads the surface signal by up to several weeks. The relative contributions, however, of potentially relevant stratospheretroposphere coupling mechanisms are not yet fully understood. In this study the relative roles, of (i) the downward effect of the zonal-mean secondary circulation induced by quasi-geostrophic (QG) adjustment to stratospheric wave drag and radiative damping and (ii) of wave drag local to the troposphere, are estimated. For this purpose, a spectral tendency equation of the QG zonal-mean zonal wind is derived, and used, in a first step, to obtain the external mechanical forcing which, in the QG framework, drives exactly the observed stratospheric and tropospheric daily NAM. In a second step, the equation is then integrated in time to reconstruct the daily NAM, but with the forcing restricted to either stratospheric or tropospheric levels, each case leaving a characteristic NAM surface signal. The relative roles of the above-mentioned mechanisms are found to be of similar quantitative importance, but to differ in a qualitative sense. The downward effect of stratospheric QG adjustment is responsible for the initiation of the NAM surface signal, whereas subsequently local tropospheric wave drag actively maintains and persists the signal over several weeks. Furthermore, the downward effect of QG adjustment to stratospheric radiative damping is shown to have only a minor impact, compared to that from stratospheric wave drag. The robustness of these conclusions is demonstrated by a sensitivity study with respect to various model parameters.