Dynamic response of monsoon precipitation to mineral dust radiative forcing in the West Africa region

Abstract

Mineral dust over West Africa region modulates summer monsoon through direct radiative forcing. This study examined the impact of mineral dust radiative forcing on West Africa Monsoon variability with the aid of Regional Climate Model (RegCM4) at 50 km grid resolution driven by ERA Interim re-analysis. Three experiments were performed; first with the non-dust aerosol version of the model (CONTROL), and second with the dust aerosol module (DUST) and with an increase in the dust concentration (DOUBLE DUST). The simulation was run from October, 2004 to December, 2005 over West Africa domain with the first 3 months taken as spin up for model stability. The result shows that there was no significant change with Control and Dust case experiment but as the dust AOD increases from 1.0 to 2.0, radiation flux at the Top of Atmosphere changes from − 60 to − 80 W/m2 in the Double dust experiment. The Surface Long-wave Radiation Flux of 8.0 W/m2 remains unchanged in both cases. The Outgoing Long-wave Radiation (OLR) flux changes from 2.0 to 4.0 W/m2 indicating reduction in convective formation and as well as decrease in precipitation of 2 mm/day in the Sahel, while precipitation increases from 2 to 4 mm/day in the Guinea coast region. There was also strengthening of TEJ core and weakening of AEJ above average as dust concentration increases in some parts of the region during the monsoon period. The air temperature increases from 22.5 to 38.5 °C in both cases from coastal area to Sahelian region of West Africa. It was concluded that substantial amount of dust concentration in the atmosphere could trigger and increase radiative forcing of aerosols thereby sensitive to monsoon variability and results in enhancement of precipitation amount in the Guinea coast and reduction of precipitation amount in the Sahel region of West Africa. Meanwhile, there is need to inquire more into difference aerosol concentration per specie that can trigger or increase radiative forcing in the atmosphere.