Influence of Walker circulations on East African rainfall
Influence of Walker circulations on East African rainfall
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DOI：
10.1007/s00382-020-05579-7
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发表时间：
2021-01
期刊：
影响因子：
4.6
通讯作者：
Siyu Zhao;K. Cook
中科院分区：
文献类型：
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作者：
Siyu Zhao;K. Cook
东非附近的步行者环流确定和东非降雨的年际变化的影响进行了探讨，在多个再分析和观测降水数据集。本文研究了在三维流动中识别二维翻转环流的方法的鲁棒性。三个步行者环流与东非降雨的潜在相关性，即，东非，刚果盆地，印度洋步行者环流。在9月至3月期间，印度洋步行者环流的向上和向下分支存在一致的反相关，在10月至12月期间具有最强的联系;其他两个步行者环流没有出现反相关。当印度洋步行者环流异常强（弱）时，在短雨季，东非地区降水较少（较多）。这些降雨量的变化与异常中层水汽辐散有关，主要是由于风辐散的变化而不是大气水汽。湿静能的异常水平平流在调节对流中可能是重要的，但考虑到未闭合的预算和复合物内的变化，这一论点并不具有决定性。上述关联并不表明因果关系。在使用步行者环流概念时应谨慎，因为二维流函数可能过于简化三维环流的复杂性。
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.