Extinction‐to‐backscatter ratios of Saharan dust layers derived

[1] We determine the extinction‐to‐backscatter (Sa) ratios of dust using (1) airborne in situ measurements of microphysical properties, (2) modeling studies, and (3) the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) observations recorded during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment conducted from Sal, Cape Verde during August to September 2006. Using CALIPSO measurements of the attenuated backscatter of lofted Saharan dust layers, we apply the transmittance technique to estimate dust Sa ratios at 532 nm and a two‐color method to determine the corresponding 1064 nm Sa. This method yielded dust Sa ratios of 39.8 ± 1.4 and 51.8 ± 3.6 sr at 532 and 1064 nm, respectively. Second, Sa at both wavelengths is independently calculated using size distributions measured aboard the NASA DC‐8 and estimates of Saharan dust complex refractive indices applied in a T‐Matrix scheme. We found Sa ratios of 39.1 ± 3.5 and 50.0 ± 4 sr at 532 and 1064 nm, respectively, using the T‐Matrix calculations applied to measured size spectra. Finally, in situ measurements of the total scattering (550 nm) and absorption coefficients (532 nm) are used to generate an extinction profile that is used to constrain the CALIPSO 532 n