The complex topography of East Africa poses challenges for accurate modeling of regional climate. The Turkana Channel in northwestern Kenya is an important feature because of a persistent low‐level jet (LLJ) that blows through it, which has complex interactions with local and regional rainfall. We establish the annual cycle and interannual variability of the LLJ in the ERA5, MERRA‐2, and JRA‐55 reanalyses. The jet is strongest during wet seasons in the surrounding region. Results suggest a statistically significant weakening of the LLJ over the last 30–40 years in two out of the three reanalyses. We propose an explanation based on the jet's relationship with regional warming patterns and zonal surface pressure gradients, which link the jet to larger‐scale climate dynamics including the Walker Circulation. If these changes continue in the future, there may be significant implications for rainfall including increases in northwest Kenya and decreases further inland. However, the global models used to produce climate projections vary in their simulations of the LLJ in part because they represented topography. Consequently, it is not possible to assess how future LLJ changes will affect regional climate using CMIP5 models alone. Differences between the reanalyses preclude their direct use for model evaluation. Improving the processes by which topographical observations are mapped onto model grids could lead to improvements in the simulation of the East African climate. A field campaign to measure the LLJ directly could resolve uncertainties in the literature, help constrain reanalyses, and determine which models have the most realistic LLJ representation.

中文翻译：

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重新分析和模型中Turkana低空喷气机的变异性：对降雨的影响

东非复杂的地形给准确模拟区域气候提出了挑战。肯尼亚西北部的图尔卡纳海峡是一个重要特征，因为持续不断的低空急流（LLJ）贯穿其中，这与当地和区域的降雨有着复杂的相互作用。我们在ERA5，MERRA-2和JRA-55重新分析中确定了LLJ的年周期和年际变化。在周围地区的雨季，喷气流最强。结果表明，在过去的30至40年中，三项再分析中有两项的LLJ有统计学意义的减弱。我们基于喷头与区域变暖模式和地表地表压力梯度之间的关系提出了一种解释，将喷流与更大范围的气候动力学（包括沃克环流）联系起来。如果将来继续发生这些变化，可能会对降雨产生重大影响，包括肯尼亚西北部地区的增加和内陆地区的减少。但是，用于生成气候预测的全球模型在模拟LLJ方面有所不同，部分原因是它们代表了地形。因此，仅凭CMIP5模型就无法评估未来的LLJ变化将如何影响区域气候。重新分析之间的差异使得它们无法直接用于模型评估。改进将地形观测图映射到模型网格的过程可以改善对东非气候的模拟。直接测量LLJ的野外活动可以解决文献中的不确定性，有助于限制重新分析，