Covariance of the intertropical discontinuity and African easterly jet in Sahelian wet and dry years

This study examines the covariance between the intertropical discontinuity (ITD) and African easterly jet (AEJ) over the West African Sahel in wet and dry year composites, using a decade of reanalysis data. ITD and AEJ positions are strongly correlated, with a more pronounced linear relationship across wet years due to the sensitivity to an intensified monsoonal flow. Whereas the AEJ's diurnal cycle shows little meridional displacement, its intensity and the ITD position show clear diurnal cycles. Considering land-surface controls, we find surface heat flux anomalies around 15°N to modify low-level temperature and sensible heat flux gradients, affecting the thermal wind and shifting the AEJ core to south of gradient maxima. More northward gradients, and hence a more northerly AEJ, occur in wet years, with a smaller shift in the ITD. Consequently, the ITD–AEJ distance narrows in wet years, driven by enhanced convective activity. Correspondingly, we find that peak frequencies of colder, more intense convective systems shift further north in wet years, whereas the southern location of warmer systems remains similar between composites. This is due to deep moist conditions prevailing south of the AEJ for both composites, favouring warm mesoscale convective system formation in a weakly sheared environment. In contrast, convective available potential energy and shear maxima shift north and align with the AEJ in wet years, displacing the environment for colder storm development. The ITD shows less sensitivity to anomalies in surface processes but may influence isolated storm events close to its positioning. These findings improve understanding of ITD–AEJ interactions and their sensitivity to soil moisture conditions, highlighting the need for high-resolution modelling to capture local feedback mechanisms.