Comparison of optical and microphysical properties of pure Saharan mineral dust observed with AERONET Sun photometer, Raman lidar, and in situ instruments during SAMUM 2006

Journal of Geophysical Research Atmospheres (Impact Factor: 3.43). 04/2012; 117. DOI: 10.1029/2011JD016825


1] The Saharan Mineral Dust Experiment (SAMUM) 2006, Morocco, aimed at the characterization of optical, physical, and radiative properties of Saharan dust. AERONET Sun photometer, several lidars (Raman and high-spectral-resolution instruments), and airborne and ground-based in situ instruments provided us with a comprehensive set of data on particle-shape dependent and particle-shape independent dust properties. We compare 4 measurement days in detail, and we carry out a statistical analysis for some of the inferred data products for the complete measurement period. Particle size distributions and complex refractive indices inferred from the Sun photometer observations and measured in situ aboard a research aircraft show systematic differences. We find differences in the wavelength-dependence of single-scattering albedo, compared to light-scattering computations that use data from SOAP (spectral optical absorption photometer). AERONET data products of particle size distribution, complex refractive index, and axis ratios were used to compute particle extinction-to-backscatter (lidar) ratios and linear particle depolarization ratios. We find differences for these parameters to lidar measurements of lidar ratio and particle depolarization ratio. Differences particularly exist at 355 nm, which may be the result of differences of the wavelength-dependent complex refractive index that is inferred by the methods employed in this field campaign. We discuss various error sources that may lead to the observed differences. Citation: Müller, D., et al. (2012), Comparison of optical and microphysical properties of pure Saharan mineral dust observed with AERONET Sun photometer, Raman lidar, and in situ instruments during SAMUM

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    • "The impact of the particle shape on single scattering optical properties , such as the asymmetry parameter and single scattering albedo , may be small (Yang et al., 2007; Otto et al., 2011), but it is larger on polarimetric optical properties (Müller et al., 2010, 2012). Thus, for nonspherical conditions, the assumption of a simplified spherical shape will cause large differences in optical property calculations (Lenoble et al., 2013) and great uncertainties in radiative forcing simulations (Kahnert et al., 2007; Yi et al., 2011). "
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    • "More recently, size distributions from in situ aircraft sampling during the SAMUM-1 and Fennec 2011 campaign showed a significant discrepancy in comparison with AERONET for larger particles (i.e. diameters >6 lm), with the inversions tending towards finer distributions compared to the aircraft samples (Muller et al., 2012; Ryder et al., 2013a,b). 3.3.2. "
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