INTERPRETATION OF LIDAR DEPOLARIZATION MEASUREMENTS OF THE PINATUBO STRATOSPHERIC AEROSOL LAYER DURING EASOE

During the EASOE campaign in the Arctic, all lidar measurements showed total depolarization values for the Pinatubo stratospheric aerosol la yer varying between 2% and 4%. If multiple scattering is negligible, t he radiation backscattered by a polydispersion of spheres has the same polarization as the incident light. There is always some depolarizati on of a lidar return because of the anisotropy of the polarizability o f the air molecules, but depolarization in the signal returned from ae rosols indicates the presence of non-spherical particles. In this pape r, we utilize scattering calculations for non-spherical particles to e xplore interpretations of lidar signals returned by Pinatubo aerosols. Taking into account several particle shapes and lognormal size distri butions, calculations show that only slightly-to-moderate deformed sph eres with equivalent-mean-radius less then 0.2 mum yield depolarizatio n values in the range given by the lidar measurements, if such particl es form a substantial fraction of the population. The implications of particle non-sphericity on the retrieval of the aerosol size distribut ion are discussed.