THE LIFETIME OF LEEWAVE-INDUCED ICE PARTICLES IN THE ARCTIC STRATOSPHERE .1. BALLOONBORNE OBSERVATIONS

During the European Arctic Stratospheric Ozone Experiment (EASOE) in 1 991/1992 there were only a few occasions when polar stratospheric clou ds (PSCs) were observed. One of these was on 27 January 1992 when PSCs were detected by two balloonborne aerosol instruments released from E srange near Kiruna, Sweden (68-degrees-N). High concentrations of part icles were found at altitudes between 19 and 24 km, in a series of man y very thin layers. Particles as large as 5 mum were detected. The sur face area concentration in the densest layers exceeded 100 mum2 cm-3, as estimated from retrieved size distributions. Estimates of the total mass of the particles suggest that ice must have been the main consti tuent, although the air temperature was 3 K or more above the frost po int. The particles were probably formed during leewave cooling over th e Norwegian mountains, some hours earlier, and some 300 km upstream of the measurements. A possible explanation for the slow evaporation obs erved is offered in part II of this paper (Peter et. al., this issue).