收稿日期: 2009-12-09
修回日期: 2010-05-19
网络出版日期: 2011-09-08
基金资助
国家自然科学基金项目(40506007、40876002、40890155); 国家科技部项目(2005CB422302)
A preliminary study on the asymmetry of ENSO and its mechanism
Received date: 2009-12-09
Revised date: 2010-05-19
Online published: 2011-09-08
利用 SODA(Simple Ocean Data Assimilation)资料, 以 Nino3.4 区 SSTA(sea surface temperature anomaly)指数
为标准, 选取典型 El Niño 和 La Niña 事件进行合成分析, 观察 ENSO 的非对称性。通过分析 ENSO 事件发生过程
中温跃层深度异常和斜压能量转化率的变化, 研究其对 ENSO 循环非对称性的影响。由于与 ENSO 相关的海洋异
常信号在南、北太平洋的传播主要是以 Rossby 波的形式, Rossby 波可以通过不稳定机制获得能量成长和传播, 斜
压能量转化率越强, 携带ENSO相关海洋异常信号的Rossby波就可能获得更多的能量成长, 这种信号传播至赤道
区域可以更快地导致 ENSO 事件的爆发。研究表明, 在 El Niño 事件达到顶峰时,北太平洋 ENSO 相关的 Rossby
波传播区斜压不稳定能量很强（可使 Rossby 波增幅） 、温跃层加深（可使 Rossby 波加速） ，有利于 El Niño 相关
的暖信号传出，这很好地解释了 El Niño 事件总是比 La Niña 事件振幅大以及 El Niño 事件向 La Niña 事件转化比
La Niña 事件向 El Niño 事件转化快很多的现象。因为强斜压不稳定能量和加深的温跃层促使携带异常信号的
Rossby波吸收能量成长和传播, 这使得El Niño事件时东太平洋暖信号更容易西传, El Niño事件更快地衰退, 并迅
速向 La Niña 事件转化，这样可以解释 ENSO 循环的不对称现象。
于毅 ,孟祥凤 ,张磊 ,赵杰臣 . ENSO 循环的非对称性及其机制初步探讨[J]. 热带海洋学报, 2011 , 30(4) : 31 -37 . DOI: 10.11978/j.issn.1009-5470.2011.04.031
The Simple Ocean Data Assimilation (SODA) product is used to make composite analysis about El Niño and La
Niña events discerned by the sea surface temperature anomaly (SSTA) in the Nino3.4 region. We analyze the asymmetry of the
El Niño-Southern Oscillation (ENSO) events and its mechanism. The difference between the distributions of baroclinic energy
conversion rate and thermocline depth anomaly of composite El Niño and La Niña events is analyzed to find their influence on
the asymmetry of ENSO. Due to the fact that ENSO-related anomalous signals travel mainly in the form of Rossby waves in
the North and South Pacific where the Rossby waves can get energy to grow by unstable mechanism, the larger the baroclinic
energy conversion rate is, the more energy the ENSO-related Rossby waves can obtain to grow. Many researches have shown
that, there is a large domain with significant unstable energy and deeper thermocline in the North Pacific in El Niño events.
Larger baroclinic instable energy helps to enlarge the amplitude of Rossby wave and deeper thermocline helps to speed up
Rossby waves. This explains why the amplitude of SSTA during El Niño events is usually larger than that in La Niña events
and why the process that El Niño transfers into La Niña takes shorter time than the one that La Niño transfers into El Niño.
Baroclinic instable energy forces the Rossby wave to absorb energy to grow, which make it easy for the warm signal propa-
gating to the east and the El Niño transfers into La Niño quickly. So the asymmetry of ENSO can be explained.
Key words： ENSO cycle; asymmetry; the North Pacific; baroclinic instability
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