L. Stefanutti , A. Kentarchos , R. MacKenzie , V. Santacesaria and Th. Peter

European Economic Interest Group – GEOPHYSICA, Florence, Italy.
Environmental Research & Services (ERS-Srl), Florence, Italy.
University of Lancaster, Dept. of Environmental Sciences, Lancaster, UK.
Previously with IROE-CNR, Florence, Italy.
ETH, Zurich, Switzerland.

We present a brief description of the Russian high-altitude aircraft M55-Geophysica, as a platform for atmospheric measurements. Special attention is given to the lidar systems on-board: a) a high power lidar emitting at 1064, 532 and 355 nm, able to detect aerosols from 1 to 10 km vertically, either above or below the aircraft (ABLE), b) a microjoule lidar, measuring parallel and perpendicular polarisation backscatter signals at 532 nm, few kilometres below and above the aircraft (MAL) and c) a miniaturised aerosol sampler which operates like a back-scatter-sonde, measuring both direct and cross polarisation at 532 mn (MAS). The payload is complemented by instruments performing in-situ measurements of aerosol size distribution, water vapour (total and gaseous), HNO₃, O₃, N₂O, SF₆, CFC-11, CFC-12, CH₄, NOy, ClO, BrO and vertical columns of O₃ and NO₂. The unique flying capabilities of the M55-Geophysica (maximum altitude 21 km, payload weight: 2.200 kg, flight range: 5 hours), make it a unique scientific platform for the study of the polar ozone loss and the chemical/physical properties of the tropical upper troposphere/lower stratosphere region. Here, we present results from the APE-THESEO tropical campaign, which took place in the western Indian Ocean (Seychelles) during February-March 1999, deploying both the M55-Geophysica and the German DLR Falcon. The main scientific issues associated with the campaign were the characterisation of the tropical tropopause region, the correlation between different stratospheric tracers and the physical/chemical properties of cirrus clouds near the tropopause and their role in the dehydration of the lower stratosphere. Of particular interest was the detection (remote and in-situ, for the first time) of particularly thin cirrus formations just below the tropopause, which can exist for days, as a homogeneous distinct cloud, covering areas of thousand kilometres, but with a vertical extend of only 200-300 m.