MULTIWAVELENGTH LIDAR MEASUREMENTS OF STRATOSPHERIC AEROSOLS ABOVE SPITSBERGEN DURING WINTER 1992 93

Within the period of December 1992 to March 1993 lidar investigations of stratospheric aerosols were performed at Ny-Alesund, Spitsbergen (79-degrees-N, 12-degrees-E). Backscatter signals at wavelengths of 353, 532 and 1064 nm and depolarization signals at 532 nm in altitudes ranging from the tropopause up to 30 km were analyzed. Throughout the whole measurement period we observed an aerosol layer of volcanic origin in the lower stratosphere. Depolarization profiles suggest that the volcanic aerosol layer consisted mainly of liquid droplets. Comparison with model calculations indicate median particle radii between 0.1 and 0.2 mum. Surface densities exceeded approximately 40 mum2/cm3 in the lower part of the layer around 12 km. In January 1993 polar stratospheric clouds (PSCs) were frequently observed at altitudes up to 22 km. We analyzed the backscatter and depolarization data with respect to the temperature history of backward trajectories reaching Ny-Alesund. Signatures for micron sized crystalline PSC particles appear for cooling rates of -1 to -3 K day-1. Larger cooling rates of -4 to -10 K day-1 produced submicron sized aerosols, presumably supercooled droplets, characterized by enhanced backscatter ratios and reduced depolarization.