POLAR STRATOSPHERIC CLOUD OBSERVATIONS OVER THE ANTARCTIC CONTINENT AT DUMONT-DURVILLE

The Istituto di Ricerca sulle Onde Electromagnetiche (IROE) two-channel elastic backscattering lidar [Sacco et al., 1989], suitable for depolarization measurements, has been operated since January 8, 1989, at the French Antarctic base of Dumont d'Urville (66-degrees 40'S, 140-degrees 01'E). A continuous monitoring of the stratosphere was performed, which permitted measurement of the evolution of the background stratospheric aerosols and of polar stratospheric clouds (PSC) throughout the year. The data reported in this article correspond to the first year of measurements. Depolarization of the lidar signals was measured in order to obtain information on the type of clouds observed and on their particle size distribution. Both low (< 10%) and high (> 10%) depolarization ratios were detected, permitting discrimination between types Ia, Ib, and II PSC according to the classification given by Toon et al. (1990). Temporal continuity and high time resolution of the lidar measurements are evidence for altitude decreases in the PSC layers over periods of a few hours. These motions, if linked to sedimentation processes, led to values of velocity (congruent-to 10 cm s-1) compatible with large particles.