African Easterly Jet Response to Changes in the Atmospheric Thermal Heating in CMIP6 Models over Central Africa

The mid-level components of the African easterly jets (AEJ-N and AEJ-S) are pan-African features that play an important role in controlling Africa's weather and climate, particularly influencing rainfall patterns in the central region. Dynamically linked to atmospheric thermal structures and moisture, how fast their structure will change in the future remains unclear. Here, we use CMIP6 models to investigate the influence of climate forcing on AEJ representation, assess the plausibility of model projections, and explore their relationship with atmospheric thermal structure under varying emission scenarios (SSP2-4.5 and SSP5-8.5). Results indicate significant variations in AEJ representation across models, with inconsistencies in their response to atmospheric thermal heating. While models such as NorESM2-LM, MRI-ESM2-0, INM-CM5-0, and MIROC6 project a strengthening AEJ-S under both SSP2-4.5 and SSP5-8.5 scenarios due to increased thermal gradients, other models like GISS-E2-1-G, CNRM-CM6-1, MPI-ESM1-2-HR, UKESM1-0-LL, and HadGEM3-GC31-LL exhibit weaker responses with AEJ-N, highlighting the complexity of underlying processes. Our findings reveal a consistent eastward shift of the AEJ-N in the high emission, models initially locate the jet over East Africa around 40°E, before it migrates towards Central Africa. The low-emission scenario offers a more credible axis orientation of the AEJ-N and AEJ-S and subsequent migration towards Central Africa, aligning with historical observations. These findings suggest that, in the Southern Hemisphere, regions south of the AEJ-S (around 20°S) are likely to experience more significant warming than Northern Hemisphere regions north to the AEJ-N (around 20°N). This projected increase in warming in the Southern Hemisphere is likely reinforcing the existing heat low over the Kalahari region and strengthening moisture-temperature gradients in the lower atmosphere, contributing to a stronger AEJ-S in the future. These results highlight the complexity of AEJ responses to climate change and the need for further research to improve model representations of these critical atmospheric features. Understanding these dynamics is essential for accurate projections of future climate conditions and their impacts in central Africa.