Interannual variability of East African rainfall: role of seasonal transitions of the low-level cross-equatorial flow
Interannual variability of East African rainfall: role of seasonal transitions of the low-level cross-equatorial flow
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DOI：
10.1007/s00382-020-05244-z
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发表时间：
2020-04
期刊：
影响因子：
4.6
通讯作者：
E. Vizy;K. Cook
中科院分区：
文献类型：
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作者：
E. Vizy;K. Cook
在北方春季和秋季，东非海岸的低层跨赤道气流减弱并逆转。这些过渡期嵌入东非雨季——春季长雨和秋季短雨。对 ERAI、ERA5、JRA-55 和 MERRA2 大气再分析以及 CHIRPS2 和 ARC2 降雨观测进行了检查，以提高我们对过渡期如何在年际时间尺度上变化以及这些变化与区域降雨有何关系的理解。过渡期长度与东非区域春季和秋季降雨量呈正相关。过渡期长度的变化与三个低层环流特征的季节性发展和变化有关，即南印度辐合带、南印度洋上空的马斯克林高压和阿拉伯海上空的阿拉伯高压。除了影响东非的低层水汽输送和汇聚之外，这些环流特征还相互作用，影响定义过渡期的开始和结束日期。根据长度、开始日期和结束日期构建和分析不同过渡期类型的复合材料，以区分事件类型之间的差异以及季节差异。西印度洋的海气耦合在春季过渡时比秋季更强，通过比湿度的变化改变降水。在秋季过渡期，降雨变化主要受环流变化控制。这些结果对东非的气候变化预测具有影响，例如，随着印度洋变暖。
During boreal spring and fall, the low-level cross-equatorial flow along the East African coast weakens and reverses. These transition periods are embedded within the East African rainy seasons—the spring long rains and the fall short rains. ERAI, ERA5, JRA-55, and MERRA2 atmospheric reanalyses and CHIRPS2 and ARC2 rainfall observations are examined to improve our understanding of how the transition periods vary on interannual timescales, and how these variations are related to regional rainfall. Transition period length is positively correlated with spring and fall East African rainfall regionally. Variations in transition period length are associated with the seasonal development and variability of three low-level circulation features, namely, the South Indian Convergence Zone, the Mascarene High over the South Indian Ocean, and the Arabian High over the Arabian Sea. In addition to affecting the low-level moisture transport and convergence over East Africa, these circulation features interact to influence the start and end dates that define the transition period. Composites are constructed and analyzed for different transition period types based on length, start date, and end date to distinguish differences among event types as well as seasonal differences. Air–sea coupling over the western Indian Ocean is stronger for the spring transition than for the fall, modifying precipitation through variations in specific humidity. In the fall transition period, rainfall variations are primarily controlled by circulation variations. These results have implications for climate change prediction over East Africa, for example, as the Indian Ocean warms.