Different atmospheric moisture divergence responses to extreme and moderate El Niños
Different atmospheric moisture divergence responses to extreme and moderate El Niños
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DOI：
10.1007/s00382-015-2844-2
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发表时间：
2016-07
期刊：
影响因子：
4.6
通讯作者：
Guangzhi Xu;T. Osborn;A. Matthews;M. Joshi
中科院分区：
文献类型：
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作者：
Guangzhi Xu;T. Osborn;A. Matthews;M. Joshi
在季节和年际时间尺度上，垂直积分的水分散度提供了一个有用的措施，热带大气水文循环。它反映了动力学和热力学的综合效应，并且不受蒸发量减去降水量观测的限制。对ERA中期再分析计算的热带太平洋水汽辐散场的经验正交函数（ERF）分析揭示了厄尔尼诺-南方涛动（ENSO）在年际时间尺度上的主导作用。两个EOF是捕捉ENSO信号所必需的，它们的主成分与赤道太平洋海表温度（SST）指数之间的回归关系表明，从强拉尼娜事件到极端厄尔尼诺事件的转变不是线性的。最大的线性偏差是最强的厄尔尼诺现象，我们解释说，这至少部分是因为厄尔尼诺分析无法轻易区分彼此不正交的不同响应模式。为了克服正交性约束，自组织映射（SOM）分析相同的水分散度场。SOM分析捕捉了对厄尔尼诺/南方涛动的各种反应，包括对厄尔尼诺/南方涛动分析所确定的中度和强烈厄尔尼诺现象的区分。这项工作表明，SOM的应用到大规模的气候分析的潜力，凭借其更容易的解释，放松正交性约束和它的多功能性作为一种替代的分类方法。厄尔尼诺现象和SOM分析都表明，根据厄尔尼诺现象对水文循环的反应程度、空间格局和演变路径的差异，可将其分为“中度”和“极端”厄尔尼诺现象。从水分发散的角度来看，分类显示与其他物理变量，如SST的基础上的结果一致。
On seasonal and inter-annual time scales, vertically integrated moisture divergence provides a useful measure of the tropical atmospheric hydrological cycle. It reflects the combined dynamical and thermodynamical effects, and is not subject to the limitations that afflict observations of evaporation minus precipitation. An empirical orthogonal function (EOF) analysis of the tropical Pacific moisture divergence fields calculated from the ERA-Interim reanalysis reveals the dominant effects of the El Niño-Southern Oscillation (ENSO) on inter-annual time scales. Two EOFs are necessary to capture the ENSO signature, and regression relationships between their Principal Components and indices of equatorial Pacific sea surface temperature (SST) demonstrate that the transition from strong La Niña through to extreme El Niño events is not a linear one. The largest deviation from linearity is for the strongest El Niños, and we interpret that this arises at least partly because the EOF analysis cannot easily separate different patterns of responses that are not orthogonal to each other. To overcome the orthogonality constraints, a self-organizing map (SOM) analysis of the same moisture divergence fields was performed. The SOM analysis captures the range of responses to ENSO, including the distinction between the moderate and strong El Niños identified by the EOF analysis. The work demonstrates the potential for the application of SOM to large scale climatic analysis, by virtue of its easier interpretation, relaxation of orthogonality constraints and its versatility for serving as an alternative classification method. Both the EOF and SOM analyses suggest a classification of “moderate” and “extreme” El Niños by their differences in the magnitudes of the hydrological cycle responses, spatial patterns and evolutionary paths. Classification from the moisture divergence point of view shows consistency with results based on other physical variables such as SST.