Potential predictability of the sea‐surface temperature forced equatorial East African short rains interannual variability in the 20th century
Potential predictability of the sea‐surface temperature forced equatorial East African short rains interannual variability in the 20th century
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DOI：
10.1002/qj.2338
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发表时间：
2014-12
影响因子：
8.9
通讯作者：
T. Bahaga;G. Mengistu Tsidu;F. Kucharski;G. T. Diro
中科院分区：
文献类型：
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作者：
T. Bahaga;G. Mengistu Tsidu;F. Kucharski;G. T. Diro
在这篇文章中，20世纪世纪海表温度（SST）强迫东非短雨变率的可预测性分析使用观测资料和长期大气环流模式（AGCM）模拟的集合。据我们所知，这样的分析，整个世纪使用一系列的AGCM集合模拟是第一次在这里进行。模式中的SST对东非短雨的影响的物理机制进行了研究。据发现，有大量的技能，再现东非短雨变率，鉴于SST是已知的。与以往的研究一致，它被发现，印度洋，特别是印度洋偶极子（IOD）的西极发挥主导作用的预测技巧，而印度洋以外的海表温度发挥次要作用。模式中西印度洋对东非降水影响的物理机制与以前的研究结果一致，包括对暖（冷）异常的鳃型响应，该异常导致赤道非洲上空的西风（东风）低空气流异常，并导致东非上空的水汽通量辐合（发散）。另一方面，正的厄尔尼诺-南方涛动（ENSO）异常导致东非部分地区的空间非相干减少效应，但这种关系不足以在我们的模型中提供任何预测技能。东非短雨预测技巧也分析了模型衍生的潜在的可预测性框架内，它表明，实际的预测技能是大致一致的模型潜在的预测技能。预测技巧的低频变化主要与印度洋地区以外的SST有关，可能是由于ENSO对20世纪70年代中期气候转变后印度洋对东非短雨影响的干扰增加。
In this article, the predictability of the 20th century sea‐surface temperature (SST) forced East African short rains variability is analyzed using observational data and ensembles of long atmospheric general circulation model (AGCM) simulations. To our knowledge, such an analysis for the whole 20th century using a series of AGCM ensemble simulations is carried out here for the first time. The physical mechanisms that govern the influence of SST on East African short rains in the model are also investigated. It is found that there is substantial skill in reproducing the East African short rains variability, given that the SSTs are known. Consistent with previous recent studies, it is found that the Indian Ocean and in particular the western pole of the Indian Ocean dipole (IOD) play a dominant role for the prediction skill, whereas SSTs outside the Indian Ocean play a minor role. The physical mechanism for the influence of the western Indian Ocean on East African rainfall in the model is consistent with previous findings and consists of a gill‐type response to a warm (cold) anomaly that induces a westerly (easterly) low‐level flow anomaly over equatorial Africa and leads to moisture flux convergence (divergence) over East Africa. On the other hand, a positive El Niño–Southern Oscillation (ENSO) anomaly leads to a spatially non‐coherent reducing effect over parts of East Africa, but the relationship is not strong enough to provide any predictive skill in our model. The East African short rains prediction skill is also analyzed within a model‐derived potential predictability framework and it is shown that the actual prediction skill is broadly consistent with the model potential prediction skill. Low‐frequency variations of the prediction skill are mostly related to SSTs outside the Indian Ocean region and are likely due to an increased interference of ENSO with the Indian Ocean influence on East African short rains after the mid‐1970s climate shift.