Diversity of moderate El Nino events evolution: role of air-sea interactions in the eastern tropical Pacific
Diversity of moderate El Nino events evolution: role of air-sea interactions in the eastern tropical Pacific
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DOI：
10.1007/s00382-017-4051-9
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发表时间：
2019-06-01
期刊：
影响因子：
4.6
通讯作者：
Takahashi, Ken
中科院分区：
文献类型：
--
作者：
Dewitte, Boris;Takahashi, Ken
在本文中，我们调查的发展阶段的中度厄尔尼诺事件的演变，目的是了解为什么他们中的一些没有演变为极端事件，尽管Bjerknes反馈的非线性放大的有利条件（即温暖的SST在南极冬季在赤道东太平洋）。在中等强度事件中，可分为东太平洋厄尔尼诺事件和中太平洋厄尔尼诺事件。我们首先表明，在中度厄尔尼诺事件中观察到的SST变化（即事件间变率）在远东太平洋最大（类似于西经130度以东）在南极冬季之前，这与显著的暖异常（中度EP厄尔尼诺）或弱暖与冷之间的异常通过对厄尔尼诺发展阶段各年海温距平演变过程的分析，揭示了中国太平洋地区在厄尔尼诺发展阶段中存在着一个典型的中尺度（中度CP El Nino）事件。奇异值分解（SVD）分析的SST和风应力异常的厄尔尼诺年进一步表明，事件间的SST变化与海气模式解释31%的SST和风应力之间的协方差。相关的SST型包括SST异常在南部秋季沿厄瓜多尔海岸沿着发展，在南部冬季向西扩展至130 ° W。相关的风应力模式的特点西风（东风）以西的类似130度W沿着赤道的6月至8月左右的EP（CP）厄尔尼诺事件的峰值。这种海气模式被解释为从EP厄尔尼诺事件的发展季节性Bjerknes反馈，因为它被证明是相关的开尔文波响应在其峰值相位。然而，9月出现在西经130度以东的赤道东风，抵消了与海气模态相关的SST异常的增长。在1972年和2015年的厄尔尼诺事件中，这些都特别活跃。它表明，东风连接到一个离赤道的南风离开秘鲁和厄瓜多尔的海岸。偏南风是由南极秋季发展而来的秘鲁沿海海温异常的响应。结合两个真实模拟ENSO多样性的全球气候模式（GFDL_CM2.1和CESM）的分析，讨论了我们的结果对理解季节性ENSO动力学和多样性的影响。
In this paper we investigate the evolution of moderate El Nino events during their developing phase with the objective to understand why some of them did not evolve as extreme events despite favourable conditions for the non-linear amplification of the Bjerknes feedback (i.e. warm SST in Austral winter in the eastern equatorial Pacific). Among the moderate events, two classes are considered consisting in the Eastern Pacific (EP) El Nino events and Central Pacific (CP) events. We first show that the observed SST variability across moderate El Nino events (i.e. inter-event variability) is largest in the far eastern Pacific (east of similar to 130 degrees W) in the Austral winter prior to their peak, which is associated to either significant warm anomaly (moderate EP El Nino) or an anomaly between weak warm and cold (moderate CP El Nino) as reveals by the EOF analysis of the SST anomaly evolution during the development phase of El Nino across the El Nino years. Singular value decomposition (SVD) analysis of SST and wind stress anomalies across the El Nino years further indicates that the inter-event SST variability is associated with an air-sea mode explaining 31% of the covariance between SST and wind stress. The associated SST pattern consists in SST anomalies developing along the coast of Ecuador in Austral fall and expanding westward as far as 130 degrees W in Austral winter. The associated wind stress pattern features westerlies (easterlies) west of similar to 130 degrees W along the equator peaking around June-August for EP (CP) El Nino events. This air-sea mode is interpreted as resulting from a developing seasonal Bjerknes feedback for EP El Nino events since it is shown to be associated to a Kelvin wave response at its peak phase. However equatorial easterlies east of 130 degrees W emerge in September that counters the growing SST anomalies associated to the air-sea mode. These have been particularly active during both the 1972 and the 2015 El Nino events. It is shown that the easterlies are connected to an off-equatorial southerly wind off the coast of Peru and Ecuador. The southerly wind is a response to the coastal SST anomalies off Peru developing from Austral fall. Implications of our results for the understanding of the seasonal ENSO dynamics and diversity are discussed in the light of the analysis of two global climate models simulating realistically ENSO diversity(GFDL_CM2.1 and CESM).