The Midday Atmospheric Controls on Mesoscale Convective System Intensity in Two Convection-Permitting Regional Atmosphere Models

The advent of convection permitting climate models has provided a step change in our understanding of West African Meteorology. Over this region, high spatial resolution models without convective parameterization have shown improved dynamical representation of high impact precipitation events (including storm intensities and processes such as cold pool outflows). However, there remains a need to compare the behavior of independent models at the process level to check to robustness of storm dynamic representation across models.

There is growing evidence that the nature of rainfall across the Sahel has changed markedly over the past thirty years. Presently, precipitation in the Sahel tends to fall in more intense, but intermittent burst compared to even the pre-drought era. Using two independently-designed, convection-permitting regional atmospheric models, we explore the dynamical link between the midday atmosphere preceding mesoscale convective systems systems of different intensities to ascertain whether the local atmosphere in some way controls evening storm intensities. It is found that zonal wind shear and the intensity of the African Easterly Jet are proportional to the intensity of late evening storms in the simulations, similar to observations. However, increased low level temperatures and moisture also precede the most intense rain events across West Africa suggesting a trifecta of contributing factors that allow the accumulation of potential energy in the boundary layer before particularly intense storms. Both models largely capture the same controls for storm intensity suggesting that robust and valuable scientific understanding behind the cause of particularly impactful rain events over West ASfrica can be ascertained. The results presented may give guidance on how we expect convective systems to change under global warming across West Africa.