论文标题
用于传播环形模式的涡流区域反馈模型
An Eddy-Zonal Flow Feedback Model for Propagating Annular Modes
论文作者
论文摘要
经常使用从经验正交函数（EOF）分析获得的单个模式来研究区域大规模大规模循环的变异性。 Zonal均值Zonal风的领先EOF（EOF1）的流行降级模型，称为环形模式，由一种涡流流相互作用机制组成，该机制导致EOF1的正反馈在自身上。然而，一些研究指出，在某些情况下，在观察和GCM中，在某些滞后时间之间存在EOF1和EOF2之间的强耦合，从而导致衰减振荡或繁殖环形模式。在这里，我们介绍了一个耦合的EOF1和EOF2的降级模型，该模型涉及潜在的交叉EOF eddy-Zonal流动反馈。使用该模型的分析解决方案，我们根据反馈强度得出了传播方案的存在条件。使用此模型以及理想化的GCM和随机原型，我们表明交叉反馈通过设置振荡频率来控制环形模式的持久性，在控制环形模式的持久性方面起着重要作用。我们发现，更强的交叉反馈会导致持续的环形模式较少。将耦合模型应用于南半球重新分析数据显示出强烈的交叉反馈。结果突出了考虑EOF和交叉反馈的耦合，以充分了解Zonal平均大规模循环的自然变异性的重要性。
The variability of the zonal-mean large-scale extratropical circulation is often studied using individual modes obtained from empirical orthogonal function (EOF) analyses. The prevailing reduced-order model of the leading EOF (EOF1) of zonal-mean zonal wind, called the annular mode, consists of an eddy-mean flow interaction mechanism that results in a positive feedback of EOF1 onto itself. However, a few studies have pointed out that under some circumstances in observations and GCMs, strong couplings exist between EOF1 and EOF2 at some lag times, resulting in decaying-oscillatory, or propagating, annular modes. Here, we introduce a reduced-order model for coupled EOF1 and EOF2 that accounts for potential cross-EOF eddy-zonal flow feedbacks. Using the analytical solution of this model, we derive conditions for the existence of the propagating regime based on the feedback strengths. Using this model, and idealized GCMs and stochastic prototypes, we show that cross-EOF feedbacks play an important role in controlling the persistence of the annular modes by setting the frequency of the oscillation. We find that stronger cross-EOF feedbacks lead to less persistent annular modes. Applying the coupled-EOF model to the Southern Hemisphere reanalysis data shows the existence of strong cross-EOF feedbacks. The results highlight the importance of considering the coupling of EOFs and cross-EOF feedbacks to fully understand the natural and forced variability of the zonal-mean large-scale circulation.
