Uncertainty in the future evolution of tropical rainfall is linked to circulation changes under warming. In Africa, a key barrier to interpreting rainfall changes is our limited understanding of water vapor transport across the continent. Here, we show that a series of nocturnal easterly Low‐Level Jets (LLJs), which form in the valleys punctuating the East African rift system, transport the majority of water vapor to central Africa from the Indian Ocean. There is a robust connection between strengthened LLJs and drought in eastern and southern Africa at interannual timescales, mediated by an increase in low‐level divergence and water vapor export. Analysis of climate model simulations at a wide range of resolutions (250–4.5 km) suggests that grid lengths <60 km are needed to simulate the salient structures of LLJs. The failure of coarse resolution models to capture LLJs is linked with biases in rainfall climatology and variability across the continent.

中文翻译：

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非洲低空喷气机及其在水汽运输和降雨中的重要性

热带降雨未来演变的不确定性与变暖下的循环变化有关。在非洲，解释降雨变化的主要障碍是我们对整个非洲大陆水汽输送的了解有限。在这里，我们展示了一系列夜间东风低空急流（LLJ），它们形成于贯穿东非裂谷系统的山谷中，将大部分水蒸气从印度洋输送至中非。在低水平散度和水蒸气出口增加的介导下，东部和南部非洲东部和南部干旱在年际尺度上与干旱之间有着密切的联系。在各种分辨率（250-4.5 km）下对气候模型模拟的分析表明，要模拟LLJ的显着结构，需要网格长度小于60 km。