The impact of soil moisture perturbations on the initiation of convection over West Africa

Numerous studies have demonstrated that convection during the West African Monsoon (WAM) is significantly influenced by the land and vegetative properties of West Africa. Yet a clear understanding of the effects of surface properties such as soil moisture and surface heat fluxes on the physical processes and life cycles of moist convection is still lacking. This research will utilize the Weather Research and Forecast Model version 2 (WRF) and an unparalleled, comprehensive observational data set collected during the field portion of the African Monsoon Disciplinary Analyses, to analyze the initiation of a Mesoscale Convective System (MCS) over an observed perturbation in soil moisture in the Sahel Region of Africa.

Airborne in-situ and remotely sensed satellite measurements have indicated that a preexisting positive perturbation in soil moisture (upwards of 150 km2) over a vegetatively sparse region in the African Sahel likely contributed to the initiation of a long-lived MCS on 31 July 2006. Observations showed that the perturbations in sensible and latent heat fluxes over the wetter soil produced a markedly cooler and moister planetary boundary layer (PBL) than over the dryer unperturbed areas. Using the vast array of observations and a high resolution WRF simulation (horz resolution of 1.66-km), this study will evaluate and attempt to simulate the impact of the soil moisture perturbations on the development of a thermally direct mesoscale circulation which contributed to the initiation of the MCS. A detailed assessment of the modeled surface fluxes and PBL evolution against observations will also be performed.