The Intrinsic 150‐Day Periodicity of the Southern Hemisphere Extratropical Large‐Scale Atmospheric Circulation
The Intrinsic 150‐Day Periodicity of the Southern Hemisphere Extratropical Large‐Scale Atmospheric Circulation
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DOI：
10.1029/2022av000833
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发表时间：
2023-05
期刊：
影响因子：
8.4
通讯作者：
Sandro W. Lubis;P. Hassanzadeh
中科院分区：
文献类型：
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作者：
Sandro W. Lubis;P. Hassanzadeh
南半球（SH）的热带外大尺度环流的变率是由南方环形模式（SAM），其时间尺度被广泛用作评估国家的最先进的气候模式的关键指标占主导地位。过去的观测和理论研究表明，SAM缺乏任何内部产生的（固有的）周期性。在这里，我们表明，使用观测和气候模型层次结构，SAM有一个内在的150天的周期性。这种周期性是鲁棒检测的功率谱和主振荡模式（又名动力模式分解）的纬向平均环流，并在半球尺度降水和海洋表面风应力。150天的周期与SAM的新降阶模型的预测一致，这表明这种周期性与湍流涡旋和纬向风异常的复杂相互作用有关，因为后者从低纬度传播到高纬度。这些发现提出了一个罕见的例子周期振荡所产生的内部动力学的extratrophic湍流环流。基于这些研究结果，我们进一步提出了一个新的度量评估气候模型，并表明，一些以前报道的缺点和改进，在模拟SAM的变化连接到模型的能力，在再现这种周期性。我们认为，这种周期性应考虑在评估气候模式和理解过去，现在，和预计南半球气候变率。
The variability of the Southern Hemisphere (SH) extratropical large-scale circulation is dominated by the Southern Annular Mode (SAM), whose timescale is extensively used as a key metric in evaluating state-of-the-art climate models. Past observational and theoretical studies suggest that the SAM lacks any internally generated (intrinsic) periodicity. Here, we show, using observations and a climate model hierarchy, that the SAM has an intrinsic 150-day periodicity. This periodicity is robustly detectable in the power spectra and principal oscillation patterns (aka dynamical mode decomposition) of the zonal-mean circulation, and in hemispheric-scale precipitation and ocean surface wind stress. The 150-day period is consistent with the predictions of a new reduced-order model for the SAM, which suggests that this periodicity is tied with a complex interaction of turbulent eddies and zonal wind anomalies, as the latter propagate from low to high latitudes. These findings present a rare example of periodic oscillations arising from the internal dynamics of the extratropical turbulent circulations. Based on these findings, we further propose a new metric for evaluating climate models, and show that some of the previously reported shortcomings and improvements in simulating SAM’s variability connect to the models’ ability in reproducing this periodicity. We argue that this periodicity should be considered in evaluating climate models and understanding the past, current, and projected Southern Hemisphere climate variability.