Lidar Determinations of Atmospheric Ice Crystal Layers at South Pole during Clear-Sky Precipitation

Abstract

Results of lidar measurements of atmospheric ice crystal layers during 36 clear-sky precipitation events at South Pole (2850 m MSL) during the winter over the period March-November 1975 are presented and correlated with ice crystal replicator, radiosonde and visual data. Low-lying ?precipitation? and higher ?formation? layers were frequently discerned in the lidar returns. In 25% of the events a single surface layer was observed with intermittent or no higher layers present. It was determined from the backscatter profiles that the crystals were growing in the precipitation layer in more than 50% of the events. The average altitudes of the precipitation layer tops during austral night and day were 420 ± 130 m and 650 ± 170 m, respectively, while the average altitudes of the temperature inversion tops for the same two periods were 580 ± 200 m and 500 ± 150 m, respectively. The lidar returns for a few days before and a few days after sunrise (21 September) were unique; high, geometrically thick layers up to 8000 m were observed which were often much more strongly scattering than the precipitation layer, yet were still optically thin. Wind data for the 36 events showed that the direction at the 650 and 600 mb levels was predominately upslope. The principal ice crystal habits observed were plates, prisms, bullets and clusters, ranging in size from 80 to 225 ?m.