On occurrence of type II PSCs over Northern Finland as observed by lidar and balloonborne sondes - Kivi, R.; Kyrö, E.; Rontu, L.; Dörnbrack, A.; Müller, M.; Wedekind, C.; Wille, H.; Stein, B.; Rizi, V.; Redaelli, G.; Mitev, V.; Matthey, R.; et al. (1999)