Direct and indirect radiative forcing of biomass burning aerosols at Kilimanjaro

Receding glaciers at the peaks of Kilimanjaro has been attributed to large scale changes in tropical climate. However, prior studies suggest that regional deforestation and atmospheric aerosols could also impact the regional climate at Kilimanjaro. Our prior investigations examined the impact of land use on the regional climate of Kilimanjaro during the dry season and found that whereas the lower elevations are impacted, effects at higher elevations are not significant. Seasonal variation of satellite derived aerosol optical thickness (AOT) shows a pronounced maximum (~0.6) in the dry season over Kilimanjaro due to biomass burning. Satellite derived AOT in combination with radiative transfer modeling was utilized to determine shortwave radiative forcing at the surface. Estimates thus derived show instantaneous shortwave radiative forcing in excess of 50 Wm^-2 during the time of morning satellite overpass (~1030 LST). Initial analysis suggests that direct aerosol radiative forcing potentially mitigates the effects of large scale climate forcing. The analysis is being extended to other seasons and also to compute diurnally average estimates of radiative forcing at the surface. In addition, numerical modeling is being utilized to examine the impact of biomass burning on orographic cloud formation over Kilimanjaro though the modulation of slope flows and the resulting indirect radiative forcing.