Evidence for Liquid Droplets in a -65° Cold Cirrus Observed by LIDAR above Sodankyla (Finland) during SESAME

Schliersee, Germany

It is widely accepted that pure water cannot exist as liquid below about -40°C. Theoretical and laboratory studies confirm this behavior for pure water . Nevertheless, liquid droplets have been seldom observed in cirrus clouds down to -50°C. Miltiwaveleght depolarization LIDAR tecnique can help ti hunt usually cold supercooled clouds. The presence of non-depolarizing cloud layers is indicative of scattering with ylindrical symmetry, possible both with spherical droplets and with ice plates horizontally oriented. In this work, a -65°C cold, non- depolarizing cloud observed in Finland is analysed, concluding thath supercooled droplets are responsible for the absence of depolarization in most of the layer.