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 the jet and its contribution to Sahel precipitation are simulated in climate models. This study examines the capabilities of Coupled Model Intercomparison Project phase six (CMIP6) models in simulating the WAWJ and its influence on Sahel precipitation. We combine the Climate Research Unit (CRU) observations with the European Centre for Medium‐Range Weather Forecast (ECMWF) Atmospheric Reanalysis (ERA5), the Modern‐Era Retrospective analysis for Research and Applications, version 2 (MERRA‐2) and the National Centres for Environmental Prediction (NCEP) Climate Forecast System Reanalysis version 2 (CFSR‐2) to evaluate 25 CMIP6 models. The majority of the models capture the temporal and spatial structure of the jet and agree with ERA5 that the jet features its core at 925 hPa and attains its maximum speed in August. However, the jets form earlier and are stronger in most models than in reanalysis. Although most CMIP6 simulations capture the link between the jet and the temperature distribution over West Africa, they struggle to reproduce the relationship with precipitation, especially over the Sahel. Most simulations fail to replicate the increase in moisture transport (i.e., the eastward and north‐eastward transports) associated with stronger WAWJ. Some simulations capture the increased moisture transport but do not translate to increased precipitation over the Sahel. The results of the study show that improving the simulation of Sahel rainfall requires a concerted effort on enhancing the model capability to better represent WAWJ.

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