The dual microphysical behavior of Namibia-Angola marine boundary layer clouds regime during the biomass-burning season

Transport of biomass burning aerosols off the coast of Namibia/Angola has drawn increasing interest due to its strong direct radiative effect and the potential dynamical feedbacks between the atmospheric circulation, cloud cover, and the solar absorbing aerosol layer. Here, we study the less explored link between boundary layer variability, cloud microphysics, and aerosol layer. In this investigation, we make use of satellite observations from A-Train constellation, to describe a unique dual microphysical behavior of the Namibia/Angola cloud regime. The dataset for this investigation consists of collocated retrievals from AMSR-E, MODIS, CERES, and CALIOP during the biomass season of July to September of 2006, and June to September of 2007 through 2010. We find a distinctive correlation between AMSR-E liquid water path (LWP) and cloud effective radius (r_e, 3.7 μm-based retrieval), with positive correlations, south of 5^o S (r >0.4) and negative ones north of 5^o S when they are computed for cloudy scenes only. We investigate further this feature, by analyzing the dependence of the cloud properties on variations in the cloud top height (H_T). LWP correlates positively with H_T (r >0.4) throughout the domain, and is consistent with adiabatic calculations made with H_T and lifting condensation level. The correlation between r_e and H_T is negative north of 5^oS (r<-0.5). Preliminary results show that the counterintuitive behavior of r_e can be explained by changes in the distance between the base height of the aerosol layer that is present above the clouds and H_T (ΔH). In fact, over the northern part of the domain, r_e positively correlates with ΔH (r>0.4), indicating that r_e becomes smaller when the aerosol layer remains closer to the cloud top, independent of the aerosol optical depth. Furthermore, we will show an evidence of the Twomey effect and albedo susceptibility associated with changes in r_e.