Contribution of Ekman Transport to the ENSO Periodicity Estimated With an Extended Wyrtki Index
Contribution of Ekman Transport to the ENSO Periodicity Estimated With an Extended Wyrtki Index
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DOI：
10.1029/2021gl095193
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发表时间：
2021-11
影响因子：
5.2
通讯作者：
Tomoki Iwakiri;M. Watanabe
中科院分区：
文献类型：
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作者：
Tomoki Iwakiri;M. Watanabe
主要驱动地转输送的离赤道风应力旋度异常对于由补给-释放过程引起的厄尔尼诺-南方涛动（ENSO）的相变至关重要。ENSO引起的纬向风应力异常也驱动了地面Ekman流，这可能会抵消地转输送，但其对ENSO周期性的影响在补给振子理论中仍然不清楚。在这里，我们扩展了ENSO诊断框架，称为Bjerknes-Wyrtki-Jin指数，以评估Ekman运输。应用于再分析数据集的扩展方法表明，ENSO周期延长约30%，调和观测到的ENSO频率和传统方法的估计之间的差异。这一结果表明，Ekman输送的自抑制过程是观测到的ENSO周期性的内在特征。此外，Ekman传输有效地与ENSO的广泛纬向结构，这表明个别ENSO事件的纬向宽度解释了它们持续时间的差异。
Off‐equatorial wind stress curl anomalies that mainly drive geostrophic transport are essential for the phase transition of the El Niño‐Southern Oscillation (ENSO) induced by a recharge‐discharge process. The ENSO‐induced zonal wind stress anomaly also drives surface Ekman currents, which may counteract the geostrophic transport, but its effect on ENSO periodicity remains unclear in the recharge oscillator theory. Here, we extended an ENSO diagnostic framework, called the Bjerknes‐Wyrtki‐Jin index, to evaluate Ekman transport. The extended method applied to reanalysis data sets shows that the ENSO period lengthens by approximately 30%, reconciling the discrepancy between the observed ENSO frequency and estimates from the conventional method. This result demonstrates that the self‐inhibitory process by Ekman transport is an inherent feature of the observed ENSO periodicity. In addition, Ekman transport efficiently works with a wide meridional structure of ENSO, suggesting that the meridional width of individual ENSO events explains the difference in their duration.