Climatology of polar stratospheric clouds based on lidar observations from 1993 to 2001 over McMurdo Station, Antarctica

Abstract

A climatology of polar stratospheric clouds (PSCs) based on lidar measurements performed at McMurdo Station, Antarctica (78°S, 167°E) from 1993 to 2001 is presented here. The observations are discussed in terms of occurrence and temporal and spatial variability of PSC types. The climatological analysis reveals that in McMurdo PSCs mainly occur between July and mid‐August. During this time their altitude changes from 22 to 14 km, following the stratospheric temperature minimum trend. At the beginning of the accounted period (1993–1994), volcanic aerosols from the Mt. Pinatubo eruption in 1991 were still present in the southern polar vortex. Therefore these 2 years have been corrected for the direct contribution of the volcanic aerosol to the backscatter signal. A close examination of the data set evidences that most PSCs appear either as rather thin layers (<1 km) or as layers with a considerably higher thickness. Therefore all observed PSCs have been divided into two classes, depending on the variation of the backscattering ratio with respect to the altitude (e.g., small‐scale variations, or SSV, and large‐scale variations, or LSV). The seasonal behavior and the occurrence of PSC types under each class have been studied, keeping 1993 and 1994 separated to better highlighting the effect of the volcanic aerosol load on cloud properties. Finally, in order to shed some light on PSC formation, back‐trajectory analysis has been performed for retrieving thermal histories of opportunely selected PSCs.