Impact of surface interactivity on the initiation of deep convection in the Sahel: A cloud-resolving model study

Année de publication

2026

Convection is strongly influenced by the surface sensible heat flux. Despite the strength of this flux in the Sahel, it is sometimes insufficient to trigger deep convection (DCV). Observations show that DCV preferentially develops over mesoscale areas that are warmer than their surroundings or slightly downstream of the large-scale low-level wind, with the thermal contrast often stemming from prior rainfall. Indeed, simulations with prescribed surface sensible heat flux have shown that mesoscale breezes converge towards these warm patches, facilitating updrafts above. This study examines the role of surface-atmosphere-radiation scheme interactions in modulating DCV, using a more realistic, interactive land surface. Results indicate that, under initially homogeneous surface conditions, surface coupling generates "small-scale" flux heterogeneities, in the order of a few kilometres, that enhance boundary-layer turbulence and deepens the mixed layer, leading to greater moisture availability near the inversion. Every stage of convection development occurs about 30 min earlier than in the prescribed surface case. When a warm mesoscale patch is introduced, DCV initiation is advanced, albeit to a lesser extent than in simulations with a prescribed surface. This can be attributed to the substantial variance in sensible heat flux of the interactive surface with and without the patch on a smaller scale than the patch itself. Consequently, the interactive surface tends to smooth the local contrasts through the patch, reducing its impact. These findings highlight the crucial role of land-atmosphere interactions and surface heterogeneity in modulating the timing and development of Sahelian convection.</div>

  Accès à la notice sur le site du portail documentaire de Météo-France

  Liste complète des notices publiques