Lidar Studies of Stratospheric Clouds in the Antarctic and the Arctic

Polar Stratospheric clouds (PSCs) are involved in the ozone depletion. During the winter season, ozone depletion is rather slow, and confined to the outer edge of the polar vortex; but heterogeneous chemical reactions on or in PSCs prime the air for ozone destruction by converting inert chlorine reservoir species into more reactive forms. PSCs are also responsible for denitrification of the lower stratosphere. Since 1988, ground-based LIDAR regular observations have been performed systematically by stations located in the Polar regions. In this paper we present a climatology using ground-based LIDAR measurements performed from 1989 to 1997 at an Antarctic station located in Doumont d'Urville (66.40S 140.01 E). It has been collected a data base of the lower Antarctic stratosphere, including aerosol background and observations of polar stratospheric clouds (PSCs). The present work focuses on the climatology of PSCs through a data base consisting on almost 100 observations. The annual cycle of the PSCs has been studied. The first PSC are observed by lidar not before Julian day 175 (15 June) and the last not later Julian day 260 (7 September). A clear relation exists between the time in the season and the altitude and temperature of the clouds. Clouds have been classified according to their optical properties. Different types of PSC have been observed, including a new type of PSC not present in the existing classification. Strong evidence of the influence of temperature on cloud type has also been found. A similar influence has been observed regarding the period of the winter season A similar analysis has been performed also for PSC observed in Sodankila in the Arctic region and is presented in this work. Lately low stratospheric clouds have been observed also in the tropical region (Indian Ocean), during the APE-THESEO tropical campaign by means of LIDAR and other scatterometers systems installed on board of two aircraft the M-55 Geophysica and Falcon.