Ground-based measurements of airborne Saharan dust in marine environment during the NAMMA field experiment

Several episodes of airborne mineral dust transported from the Saharan deserts were observed at Sal Island, Cape Verde for 2 – 28 September 2006 during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment. Dust particles were mixed with marine background aerosols when the dust layers descended into the marine boundary layer. A new method is developed to derive the optical properties of dust when mixed with maritime aerosols. The derived single scattering albedo and mass scattering efficiency differed significantly between two selected cases leading to differences in their direct radiative effects. Back-trajectory analyses suggest that the two cases were influenced by dust particles originating from different source regions over North Africa. This stresses the importance of resolving dust optical properties in subregional scales to attain a better assessment of the role of airborne dust on the climate system.