A New Zonal Wave-3 Index for the Southern Hemisphere
A New Zonal Wave-3 Index for the Southern Hemisphere
复制标题
南半球新的第 3 波纬向波指数
DOI：
10.1175/jcli-d-21-0927.1
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发表时间：
2022
影响因子：
4.9
通讯作者：
M. England
中科院分区：
文献类型：
--
作者：
R. Goyal;M. Jucker;Alexander Sen Gupta;M. England
纬向波3（ZW 3）是南半球热带外大气环流的一个重要特征，对纬向热量和动量输送、区域南极海冰范围以及南半球阻塞事件有重要影响。过去已经尝试定义量化ZW 3模式中的可变性的指数;然而，现有方法基于固定的地理位置，并且由于相位的强可变性而未能捕获某些ZW 3事件。此外，在CMIP模型中，固定的空间索引对ZW 3的特征描述较差，这可能会在ZW 3模式的平均相位中表现出偏差。在这项研究中，我们引入了一种新的方法来表征ZW 3的变化，将两个指数，一个分别为幅度和相位，根据500 hPa纬向风异常的前两个经验正交函数（EOFs）的组合。我们发现，新的ZW 3指数比过去的指数提供了明显的优势，因为它捕获了更高比例的方差（20%比20%），它可以用于再分析数据集和耦合气候模型，无论模型偏差如何。与新指数相关的复合分析揭示了我们的指数和南极周围海冰分数定义的ZW 3之间的强关系，在不同阶段的强ZW 3事件期间具有显着的区域海冰异常。
Zonal wave 3 (ZW3) is an important feature of the Southern Hemisphere extratropical atmospheric circulation and has strong impacts on meridional heat and momentum transport, regional Antarctic sea ice extent, and Southern Hemisphere blocking events. Attempts have been made in the past to define an index that quantifies the variability in the ZW3 pattern; however, existing methods are based on fixed geographical locations and fail to capture certain ZW3 events because of strong variability in phase. In addition, a fixed spatial index poorly characterizes ZW3 in CMIP models, which can exhibit biases in the mean phase of the ZW3 pattern. In this study, we introduce a new way to characterize ZW3 variability by incorporating two indices, one each for magnitude and phase, based on the combination of the first two empirical orthogonal functions (EOFs) of the 500-hPa meridional wind anomalies. We show that the new ZW3 index provides a clear advantage over past indices because it captures a substantially higher proportion of variance (∼40% compared to ∼16%), and it can be used for both reanalysis datasets and coupled climate models regardless of model biases. A composite analysis associated with the new index reveals a strong relationship between the ZW3 defined by our index and sea ice fraction around Antarctica, with significant regional sea ice anomalies during strong ZW3 events with different phases.