Characteristics of Arctic Polar Stratospheric Clouds as Measured by Airborne Lidar

Abstract

Airborne lidar measurements of backscattering at 0.6943 ?m from polar stratospheric clouds, made in January 1984, are reported. The clouds, whose altitudes and geographical locations coincided with ambient atmospheric temperatures below about 193 K, were observed to cover a greater area of the polar cap than had previously been apparent from satellite measurements. They were seen on three separate flights north of Thule, Greenland (76.5°N, 68.7°W), on one occasion extending continuously from approximately 80°N to the North Pole. Pronounced layering of the clouds was observed and the maximum backscatter enhancement, relative to that from the background aerosol, was between 100 and 200. These values occurred at an altitude of about 20 km, close to the region of minimum stratospheric temperature. Depolarization of the order of 20?50% in the backscattered signal was measured, in support of the hypothesis that the aerosols forming the clouds are frozen. Comparison of the experimentally determined backscattering-temperature relationship with a theoretical model, based on a volcanic aerosol and using best available estimates for water vapor concentration, shows good agreement at the 100- and 70-mb pressure levels. A small systematic error at the 50- and 30-mb levels may be due to inaccurate characterization of the temperature field at these altitudes and locations.