Potential Impact of the Tropical Indian Ocean-Indonesian Seas on El Nino Characteristics
Potential Impact of the Tropical Indian Ocean-Indonesian Seas on El Nino Characteristics
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DOI：
10.1175/2010jcli3396.1
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发表时间：
2010-07-01
影响因子：
4.9
通讯作者：
Hafner, Jan
中科院分区：
文献类型：
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作者：
Annamalai, H.;Kida, Shinichiro;Hafner, Jan
用20世纪(1861-2000年)地球物理流体动力学实验室气候模式2.1版(CM2.1)的集合积分进行的诊断表明，在发展阶段，与印度洋偶极子纬向模式(IODZM；1类)同时发生的厄尔尼诺事件比没有发生(2类)的厄尔尼诺事件更强。此外，在第1类事件期间，印度尼西亚海中出现了与IODZM生命周期密切相关的海面温度异常。本文研究了这些区域海温异常(赤道印度洋和印度尼西亚海)对厄尔尼诺发展的影响。对1-2级合成的检验表明：(1)在1月期间，赤道太平洋内部的海洋-大气条件有利于更强的厄尔尼诺的发展；(2)5-6月期间，与区域海温异常的发展相一致，赤道西太平洋西风异常显著增加，随后赤道东太平洋温跃层和海温异常增加。本文假设在赤道太平洋有利的条件下，区域性海温异常可以发展出更强的厄尔尼诺现象。根据CM2.1中的大量反馈，检验了5-6月异常降水强迫的线性大气模式的解和赤道印度洋-太平洋选定区域的海温异常。与我们之前的研究一致，赤道西太平洋上空净开尔文波对热带印度洋加热异常的响应被抵消。相比之下，印度尼西亚海SST异常约占赤道西太平洋西风异常的60%-80%，并诱发赤道中太平洋降水异常。认为降水和环流异常之间的反馈导致了赤道西太平洋纬向风异常的突然增加，在此基础上，作者利用海洋模式进一步研究了造成印度尼西亚海SST冷异常的过程。敏感性实验表明，局地风异常，通过更强的地表热量损失和蒸发，以及次表层上升流是主要原因。本文的结果表明，在耦合模式中，对赤道印度洋-太平洋暖池区域海-气相互作用的正确描述对于理解和预测厄尔尼诺的幅度可能是重要的。
Diagnostics performed with twentieth-century (1861-2000) ensemble integrations of the Geophysical Fluid Dynamics Laboratory Climate Model, version 2.1 (CM2.1) suggest that, during the developing phase, El Nino events that co-occur with the Indian Ocean Dipole Zonal Mode (IODZM; class 1) are stronger than those without (class 2). Also, during class 1 events coherent sea surface temperature (SST) anomalies develop in the Indonesian seas that closely follow the life cycle of IODZM. This study investigates the effect of these regional SST anomalies (equatorial Indian Ocean and Indonesian seas) on the amplitude of the developing El Nino.An examination of class 1 minus class 2 composites suggests two conditions that could lead to a strong El Nino in class 1 events: (i) during January, ocean-atmosphere conditions internal to the equatorial Pacific are favorable for the development of a stronger El Nino and (ii) during May-June, coinciding with the development of regional SST anomalies, an abrupt increase in westerly wind anomalies is noticeable over the equatorial western Pacific with a subsequent increase in thermocline and SST anomalies over the eastern equatorial Pacific. This paper posits the hypothesis that, under favorable conditions in the equatorial Pacific, regional SST anomalies may enable the development of a stronger El Nino.Owing to a wealth of feedbacks in CM2.1, solutions from a linear atmosphere model forced with May-June anomalous precipitation and anomalous SST from selected areas over the equatorial Indo-Pacific are examined. Consistent with our earlier study, the net Kelvin wave response to contrasting tropical Indian Ocean heating anomalies cancels over the equatorial western Pacific. In contrast, Indonesian seas SST anomalies account for about 60%-80% of the westerly wind anomalies over the equatorial western Pacific and also induce anomalous precipitation over the equatorial central Pacific. It is argued that the feedback between the precipitation and circulation anomalies results in an abrupt increase in zonal wind anomalies over the equatorial western Pacific.Encouraged by these results, the authors further examined the processes that cause cold SST anomalies over the Indonesian seas using an ocean model. Sensitivity experiments suggest that local wind anomalies, through stronger surface heat loss and evaporation, and subsurface upwelling are the primary causes. The present results imply that in coupled models, a proper representation of regional air-sea interactions over the equatorial Indo-Pacific warm pool may be important to understand and predict the amplitude of El Nino.