Polar stratospheric clouds of liquid aerosol: An experimental determination of mean size distribution

The determination of the mean size distribution for a Type Ib Polar Stratos pheric Cloud ("PSC") has been performed for the first time using extinction ,backscattering ratios as obtained from LIDAR data at 355, 532 and 750 nm. The multiwavelength Lidar was operated in Sodankyla, Finland, during the Se cond European Stratospheric Arctic and Middle-latitudes Experiment (SESAME, November 1994-April 1995). It produced vertical profiles of PSC. Log-norma l distributions of supercooled ternary solution (STS), composed of H2SO4-HN O3-H2O particles with mode radius of 0.68-0.9 mu m and standard deviation o f 1.1-1.4, were retrieved as best fit to experimental data. Laboratory meas urements of n(r) (real part of refractive index), in the 404-633 nm range, show that it depends on the water/acid ratio without any distinction betwee n binary and ternary solutions of nitric and sulphuric acid. (C) 1999 Elsev ier Science Ltd. All rights reserved.