Understanding how mesoscale convection interacts with synoptic-scale circulations over West Africa is crucial for improving regional weather forecasts and developing convection parameterisations to address biases in climate models. A 10-year pan-African convection-permitting simulation and a corresponding parameterised simulation for current-climate conditions are used to calculate the circulation budget around a synoptic region over the diurnal cycle, splitting processes involved in circulation tendency between diurnal mean and anomalous contributions, vorticity accumulation and vortex tilting. Dynamical fields are composited around precipitating grid cells during afternoon and overnight convection to understand how the mesoscale convection modulates these synoptic-scale processes, and these composites are compared to an observational case. The dominant process modulating circulation tendency was found to be synoptic-scale vorticity accumulation, which is similar in the two simulations. The greatest difference between the simulated budgets was the tilting term. We propose that the tilting term is affected by convective momentum transport associated with precipitating systems crossing the boundary of the region, while the stretching term relies on the convergence and divergence induced by storms within the region. The simulation with parameterised convection captures the heating profile similarly to the simulation with explicit convection, but there are marked differences in convective momentum transport. An accurate vertical convergence structure as well as momentum transport must be simulated in parameterisations to correctly represent the impacts of convection on circulation.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)