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Influence of Walker circulations on East African rainfall
Climate Dynamics ( IF 4.6 ) Pub Date : 2021-01-05 , DOI: 10.1007/s00382-020-05579-7
Siyu Zhao , Kerry H. Cook

Walker circulations near East Africa are identified and their influence on the interannual variability of East African rainfall is explored in multiple reanalyses and observational precipitation datasets. The robustness of methodology for identifying 2-dimensional overturning circulations in a three-dimensional flow is investigated. Three Walker circulations with potential relevance to East African rainfall are identified, namely, the East African, the Congo Basin, and the Indian Ocean Walker circulations. Consistent anti-correlations across the reanalyses exist for the upward and downward branches of the Indian Ocean Walker Circulation during September–March, with strongest connections during October–December; they do not emerge for the other two Walker circulations. Less (more) precipitation occurs over East Africa in the short-rains season when the Indian Ocean Walker Circulation is anomalously strong (weak). These rainfall variations are associated with anomalous mid-level moisture divergence that primarily results from variations in wind divergence rather than atmospheric moisture. The anomalous horizontal advection of moist static energy can be important in modulating convection, but this argument is not conclusive considering the unclosed budget and the variations within the composites. The associations above do not indicate causality. Caution is advisable when using the concept of Walker circulations because a two-dimensional stream function can over-simplify the complexity of the three-dimensional circulation.



中文翻译:

沃克环流对东非降雨的影响

确定了东非附近的沃克环流,并通过多次再分析和观测降水数据集探讨了它们对东非降水年际变化的影响。研究了在三维流中识别二维倾覆环流的方法的鲁棒性。确定了与东非降雨潜在相关的三个沃克环流,即东非,刚果盆地和印度洋沃克环流。在9月至3月期间,印度洋沃克环流的向上和向下分支之间存在一致的反相关关系,在10月至12月之间的联系最为紧密。它们不会在其他两个Walker循环中出现。在短雨季节,当印度洋沃克环流异常强(弱)时,东非的降水较少(较多)。这些降雨变化与异常的中层水分扩散有关,这主要是由于风扩散而不是大气水分的变化所致。湿静态能量的水平对流异常在调节对流中可能很重要,但是考虑到未封闭的预算和复合材料内部的变化,该论点不是结论性的。以上关联不表示因果关系。使用沃克环流的概念时,应谨慎行事,因为二维流函数可能会过分简化三维环流的复杂性。这些降雨变化与异常的中层水分扩散有关,这主要是由于风扩散而不是大气水分的变化所致。湿静态能量的水平对流异常在调节对流中可能很重要,但是考虑到未封闭的预算和复合材料内部的变化,该论点不是结论性的。上述关联并不表示因果关系。使用沃克环流的概念时,应谨慎行事,因为二维流函数可能会过分简化三维环流的复杂性。这些降雨变化与异常的中层水分扩散有关,这主要是由于风扩散而不是大气水分的变化所致。湿静态能量的水平对流异常在调节对流中可能很重要,但是考虑到未封闭的预算和复合材料内部的变化,该论点不是结论性的。上述关联并不表示因果关系。使用沃克环流的概念时,应谨慎行事,因为二维流函数可能会过分简化三维环流的复杂性。湿静态能量的水平对流异常在调节对流中可能很重要,但是考虑到未封闭的预算和复合材料内部的变化,该论点不是结论性的。上述关联并不表示因果关系。使用沃克环流的概念时,应谨慎行事,因为二维流函数可能会过分简化三维环流的复杂性。湿静态能量的水平对流异常在调节对流中可能很重要,但是考虑到未封闭的预算和复合材料内部的变化,该论点不是结论性的。上述关联并不表示因果关系。使用沃克环流的概念时,应谨慎行事,因为二维流函数可能会过分简化三维环流的复杂性。

更新日期:2021-01-05
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