Initiation of deep convection caused by land-surface inhomogeneities in West Africa: a modelled case study

Abstract

Simulations with the Consortium for Small Scale Modelling model were performed to investigate the impact of land surface inhomogeneities on the initiation of convection. A case from the African Monsoon Multidisciplinary Analysis campaign, 11 June 2006, was selected. On this day, a mesoscale convective system was observed and simulated. The simulation scenarios included a realistic and an increased initial soil moisture distribution as well as a homogeneous soil moisture and texture field. Land use and orography were the same in all runs. Heat and moisture budget calculations were applied to analyse the processes responsible for the evolution of pre-convective atmospheric conditions and convection-triggering thermally induced circulation systems. Convective cells were initiated in all experiments. However, the amount of cells, their origin, evolution, and precipitation amount differed. First shallow clouds were initiated over areas with higher sensible heat fluxes. The evolution of subsequent deep convection was triggered by secondary circulation systems caused by baroclinic conditions generated by clouded and unclouded regions. The further evolution of the precipitation cells strongly depended on convective inhibition in the areas the cells moved into.