The eastward shift of the Walker Circulation in response to global warming and its relationship to ENSO variability
The eastward shift of the Walker Circulation in response to global warming and its relationship to ENSO variability
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DOI：
10.1007/s00382-014-2091-y
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发表时间：
2014-11-01
期刊：
影响因子：
4.6
通讯作者：
Power, Scott B.
中科院分区：
文献类型：
--
作者：
Bayr, Tobias;Dommenget, Dietmar;Power, Scott B.
本文研究了CMIP 3和CMIP 5气候模式中步行者环流和其他纬向环流单元（用纬向流函数表示）对全球变暖的响应。呈现平均状态的变化以及变异性模式的变化。在RCP4.5和SRES A1B情景下，沿赤道沿着的多模式集合中的平均纬向环流减弱。在太平洋上空，步行者环流也显示出明显的东移。这些变化的平均环流是非常相似的主导模式的年际变化的热带纬向环流细胞，这是占主导地位的厄尔尼诺南方涛动的变化。在厄尔尼诺事件期间，环流减弱，海洋大陆上的上升分支与中性条件相比向东移动（拉尼娜事件则相反）。步行者环流的全球变暖强迫趋势的三分之二可以用这种年际变化模式的长期趋势来解释，即在全球变暖的情况下，多模式平均值向更类似厄尔尼诺的条件转变。此外，在纬向环流的年际变化表现出厄尔尼诺和拉尼娜事件之间的不对称性。与拉尼娜异常相比，厄尔尼诺异常位于更偏东的位置。与这种不对称性相一致，我们发现在全球变暖的纬向流函数的变化的主导模式的东部转移。所有这些结果在各个模型之间有所不同，但CMIP 3和CMIP 5的多模型集成在几乎所有方面都显示出非常相似的结果，这强调了这些结果的稳健性。1979年至2012年的观测数据（ERA中期再分析）显示，步行者环流向西移动并加强。这与CMIP模型的结果相反。然而，步行者环流75%的趋势可以再次解释为主要变率模式的转变，但这里更像拉尼娜现象。因此，在气候变化预测和观测中，步行者环流的长期趋势似乎在很大程度上遵循了先前存在的内部变率的主导模式。
This study investigates the global warming response of the Walker Circulation and the other zonal circulation cells (represented by the zonal stream function), in CMIP3 and CMIP5 climate models. The changes in the mean state are presented as well as the changes in the modes of variability. The mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the RCP4.5 and SRES A1B scenarios. Over the Pacific the Walker Circulation also shows a significant eastward shift. These changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells, which is dominated by El Nino Southern Oscillation variability. During an El Nino event the circulation weakens and the rising branch over the Maritime Continent shifts to the east in comparison to neutral conditions (vice versa for a La Nina event). Two-thirds of the global warming forced trend of the Walker Circulation can be explained by a long-term trend in this interannual variability pattern, i.e. a shift towards more El Nino-like conditions in the multi-model mean under global warming. Further, interannual variability in the zonal circulation exhibits an asymmetry between El Nino and La Nina events. El Nino anomalies are located more to the east compared with La Nina anomalies. Consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming. All these results vary among the individual models, but the multi model ensembles of CMIP3 and CMIP5 show in nearly all aspects very similar results, which underline the robustness of these results. The observed data (ERA Interim reanalysis) from 1979 to 2012 shows a westward shift and strengthening of the Walker Circulation. This is opposite to what the results in the CMIP models reveal. However, 75 % of the trend of the Walker Circulation can again be explained by a shift of the dominant mode of variability, but here towards more La Nina-like conditions. Thus in both climate change projections and observations the long-term trends of the Walker Circulation seem to follow to a large part the pre-existing dominant mode of internal variability.