The Turkana low-level jet stream (TJ) is important to climatic conditions over northern Kenya and East Africa. The representation of the TJ in climate models varies due to the TJ interaction with Turkana channel that is influenced by model resolution and influences the model representation of the regional climate. This study compares features of the TJ in CMIP6 AMIP model simulations with ERA5. Models reveal climatological wind speeds that match those of the reanalysis from the ERA5 at the jet entrance (13 m/s) but lower magnitudes of wind speed and vertical shears compared to ERA5 within the Turkana channel. The models with slowest wind speeds, have a flattened Turkana channel and fail to exhibit the terrain constriction at 37° E which otherwise aids in accelerating winds to form a jet core. Furthermore, they fail to represent the narrowing of the channel as in ERA5, thereby forming blocking walls in the channel, forcing vertical ascent and mixing, and weakening shear. This boosting of ascent motion promotes rainfall formation and enhances wet anomalies at the exit of the TJ when the jet stream is weaker. By applying a new narrowing index, we demonstrate the need to improve topography details in the CMIP6 models, particularly those with resolution coarser than 1.5°, in order to properly simulate the TJ and the observed rainfall over the northwestern areas of eastern Africa.

图尔卡纳低空急流（TJ）对肯尼亚北部和东非的气候条件很重要。由于 TJ 与 Turkana 通道的相互作用受模式分辨率的影响，影响区域气候的模式表示，因此气候模型中 TJ 的表示方式有所不同。本研究将 CMIP6 AMIP 模型模拟中 TJ 的特征与 ERA5 进行比较。模型显示的气候风速与 ERA5 在射流入口处的再分析结果相匹配（13 m/s），但与图尔卡纳河道内的 ERA5 相比，风速和垂直切变的幅度较低。风速最慢的模型具有平坦的 Turkana 通道，并且未能在 37° E 处表现出地形收缩，否则有助于加速风形成喷射核心。此外，它们不能像 ERA5 那样代表通道变窄，从而在通道中形成阻塞壁，迫使垂直上升和混合，并削弱剪切力。当急流较弱时，上升运动的这种促进促进了降雨的形成并增强了 TJ 出口处的湿异常。通过应用新的窄化指数，我们证明需要改进 CMIP6 模型中的地形细节，特别是那些分辨率低于 1.5° 的模型，以便正确模拟 TJ 和在东非西北部地区观测到的降雨。