How predictable is El Nino?
How predictable is El Nino?
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DOI：
10.1175/bams-84-7-911
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发表时间：
2003-07-01
影响因子：
8
通讯作者：
Wittenberg, A
中科院分区：
文献类型：
--
作者：
Fedorov, AV;Harper, SL;Wittenberg, A
没有人预料到厄尔尼诺现象在1992年会很弱和持续，但在1997/98年会很短暂和强烈。为什么各种厄尔尼诺现象如此不同，如此难以预测？答案涉及到随机大气扰动（如西风爆发）在维持弱阻尼南方涛动中所起的重要作用，其互补的暖相和冷相分别是厄尔尼诺和拉尼娜。正如阻尼摆在随机时间受到适度打击的情况一样，厄尔尼诺的可预测性是有限的，而不是像天气那样通过初始条件的误差放大，而是主要通过与南方涛动相互作用的大气扰动。根据风场的统计资料，通过一个海气耦合模式的集合计算，可以确定未来赤道东太平洋海表温度波动的概率分布函数。集合的每个成员从相同的初始条件开始，并叠加了不同的噪声实现。在1996年底作出的这种预测将使中等强度的事件比1997年实际发生的极强事件的可能性更大。(The在一九九七年年初接连吹西风的情况较为罕见。2001年下半年的情况与1996年相似，这表明2002年出现厄尔尼诺现象的可能性相对较高。事件是弱还是强取决于一年中发生的随机扰动。
Nobody anticipated that El Nino would be weak and prolonged in 1992, but brief and intense in 1997/98. Why are various El Nino episodes so different, and so difficult to predict? The answer involves the important role played by random atmospheric disturbances (such as westerly wind bursts) in sustaining the weakly damped Southern Oscillation, whose complementary warm and cold phases are, respectively, El Nino and La Nina. As in the case of a damped pendulum sustained by modest blows at random times, so the predictability of El Nino is limited, not by the amplification of errors in initial conditions as in the case of weather, but mainly by atmospheric disturbances interacting with the Southern Oscillation. Given the statistics of the wind fluctuations, the probability distribution function of future sea surface temperature fluctuations in the eastern equatorial Pacific can be determined by means of an ensemble of calculations with a coupled ocean-atmosphere model. Each member of the ensemble starts from the same initial conditions and has, superimposed, a different realization of the noise. Such a prediction, made at the end of 1996, would have assigned a higher likelihood to a moderate event than to the extremely strong event that actually occurred in 1997. (The rapid succession of several westerly wind bursts in early 1997 was a relatively rare phenomenon.) In late 2001, conditions were similar to those in 1996, which suggested a relatively high probability of El Nino appearing in 2002. Whether the event will be weak or intense depends on the random disturbances that materialize during the year.