How Well Do CMIP6 Models Simulate the Influence of the West African Westerly Jet on Sahel Precipitation?

Abstract The West African westerly jet (WAWJ) plays a crucial role in Sahel precipitation, yet there is no information on how well climate models simulate the jet and its contribution to Sahel precipitation. This study examines the capabilities of Coupled Model Intercomparison Project (version six; CMIP6) models in simulating the WAWJ and its influence on Sahel precipitation. For the study, we combine the Climate Research Unit (CRU) observation with the European Centre for Medium-Range Weather Forecast (ECMWF) Atmospheric Reanalysis (ERA5) to evaluate 26 CMIP6 simulation datasets. Defining the WAWJ as a low-level westerly jet over the eastern Atlantic and the West African coast, we extracted the characteristics of the WAWJ in the CMIP6 simulations and compared them with those from the ERA5 reanalysis. The results show that the majority of the CMIP6 models agree with ERA5 on the structure and location of the jet, except the jet forms earlier and are stronger in CMIP6 models than in ERA5. While most of the CMIP6 simulations capture the link between the jet and temperature distribution over West Africa, they struggle to reproduce the relationship between the jet and precipitation distribution over the sub-continent, especially over the Sahel. Most simulations failed to replicate the increase in the moisture transport (i.e., the eastward and north-eastward transports) associated with the stronger WAWJ as shown by ERA5. Some simulations capture the increased moisture transport but do not translate it to increased precipitation over the Sahel. This study contributes towards better simulations of Sahel precipitation in climate models.