Lidar observations of Arctic polar stratospheric clouds, 1988: Signature of small, solid particles above the frost point



Polar stratospheric clouds (PSC's) in the 21-24 km altitude range were observed north of Greenland (82-84°N, 0-25°W) on January 29, 1988, using an airborne dual-polarization, 0.532-µm wavelength lidar. Synoptic analyses at the 30-mb level (≈22 km) show local temperatures of 191-193K, which are well above the estimated frost point temperature of 185K and indicate the PSC's were likely of the binary HNO3-H2O (Type I) class. Peak scattering ratios of 1.1-1.2 were measured in the PSC layer, compared to values near 1.05 for the ambient (non-PSC) aerosol over the same altitude range. Profiles of the depolarization ratio distinctly show the PSC layer, but maximum values are 0.06-0.07, only slightly greater than the value (0.04) measured in cloud-free regions and well below the values typically found in cirrus clouds (0.2-0.5). This signature suggests that the Type I PSC's observed during the January flight were composed of small, solid particles having radii on the order of the laser wavelength (≈0.5 µm).