Nephelometer Measurements of the Asymmetry Parameter, Volume Extinction Coefficient, and Backscatter Ratio in Arctic Clouds

A new instrument, a cloud integrating nephelometer (CIN), was used on the University of Washington’s CV-580 research aircraft to measure the asymmetry parameter (g), volume scattering coefficient, and backscatter ratio in clouds in situ and in the visible spectrum during the FIRE-ACE/SHEBA field project in the late spring and summer of 1998 in the Arctic. The principle behind the operation of the CIN is described, and error estimates for the measurements are calculated. The average value of g measured with the CIN in all the Arctic clouds was 0.824, which is slightly less than the value expected for the water-containing clouds that dominated the measurements. The average value of g measured in a glaciated cloud, containing mostly large bullet rosette ice crystals, was 0.737. This relatively small value of g is compared to modeled and indirect measurements of g described in the literature, some of which gave similar small values of g.