Dynamic Causes of ENSO Decay and its Asymmetry
Dynamic Causes of ENSO Decay and its Asymmetry
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DOI：
10.1175/jcli-d-21-0138.1
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发表时间：
2021-11
影响因子：
4.9
通讯作者：
X. Song;Renhe Zhang;X. Rong
中科院分区：
文献类型：
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作者：
X. Song;Renhe Zhang;X. Rong
厄尔尼诺和拉尼娜在衰变阶段表现出不对称演化特征。厄尔尼诺的衰减速度明显大于拉尼娜。本研究通过数据分析、数值实验以及动力和热力学诊断，系统、定量地研究了赤道西太平洋（WP）和中东太平洋（CEP）风应力异常对ENSO衰减及其不对称性的相对贡献。结果表明，赤道CEP风应力异常强迫的海表温度异常（SSTA）在ENSO衰减中起主导作用，并导致ENSO衰减不对称，而赤道WP风应力异常强迫的贡献较小。对海洋混合层热收支的诊断表明，赤道CEP风应力异常引起的异常纬向平流项和垂直平流项是导致ENSO衰减的最重要动力项。厄尔尼诺衰变阶段的两项都比拉尼娜衰变阶段大得多，导致厄尔尼诺衰变阶段的衰变速度比拉尼娜阶段更大。这两项的贡献不依赖于赤道西域风场，证实了赤道西域风应力异常并不是ENSO不对称衰减的关键部分。此外，结果表明，赤道CEP中的主导贡献来自赤道中太平洋的风应力异常，其中赤道中南太平洋的风应力异常起主要作用。
El Niño and La Niña exhibit asymmetric evolution characteristics during their decay phases. The decay speed of El Niño is significantly greater than that of La Niña. This study systematically and quantitatively investigates the relative contributions of the equatorial western Pacific (WP) and central-eastern Pacific (CEP) wind stress anomalies to ENSO decay and its asymmetry through data analysis, numerical experiments, and dynamic and thermodynamic diagnoses. It is demonstrated that the sea surface temperature anomalies (SSTAs) forced by the wind stress anomalies in the equatorial CEP play a dominant role in ENSO decay and contribute to ENSO decay asymmetry, while the forcing by the equatorial WP wind stress anomalies has a small contribution. Diagnoses of the oceanic mixed layer heat budget indicate that anomalous zonal advection term and vertical advection term forced by the wind stress anomalies in the equatorial CEP are the most important dynamic terms contributed to ENSO decay. Both terms in El Niño decay phase are much larger than in La Niña decay phase, resulting in a larger decay speed in El Niño than in La Niña. The contributions of these two terms do not depend on the equatorial WP wind field, confirming that the equatorial WP wind stress anomalies do not act as a pivotal part in ENSO asymmetric decay. Moreover, it is demonstrated that within the equatorial CEP, dominant contribution comes from the wind stress anomalies in the equatorial central Pacific, in which those in the equatorial southern central Pacific play a major role.