A climatological study of polar stratospheric clouds (1989-1997) from LIDAR measurements over Dumont d'Urville (Antarctica)

Backscatter lidar data from the French Antarctic base in Dumont d'Urville ( 66.40 degreesS, 140.01 degreesE), including aerosol background and observat ions of polar stratospheric clouds (PSCs), have been collected since 1989. In the present work we present a climatological study of PSCs, using a data base consisting of almost 90 observations. The seasonal evolution of PSCs, their optical classification, and their relationship with the observation temperature were studied. The first PSC was observed on day number 175 (15 June) and the last on day number 260 (7 September). The characteristic mid- cloud altitude decreases through the season at a rate of 2.5 km/month. Type Ia, Ib, and II PSCs - identified by their optical properties have been obs erved. External mixtures of these types have also been observed. These obse rvations have been related to the local temperature measured by radiosondes . The relationship between PSC type and the period of the winter season was also investigated. Mixed (solid and liquid) type I clouds are mostly obser ved at the beginning of the winter. Type II clouds are observed only during the coldest period around midwinter, although temperatures below the frost point begin earlier and persist longer than this. Type Ia, solid-particle, clouds are observed mostly at the end of the winter.