Climatology of Polar Stratospheric Clouds based on Lidar Observations from 1993 to 2001 over McMurdo Station, Antarctica

2 A climatology of polar stratospheric clouds (PSCs) has been obtained by lidar measurements performed at from McMurdo, Antarctica (78°S, 167°E), between 1993 and 2001. The highest PSC presence is registered between July and mid-August, with a descending of the maximum occurrence according to the subsidence of the polar vortex (22 km to 14 km from mid-June to August). Between 15 May and 30 September, McMurdo is usually located inside the polar vortex and PSCs appear in the 75% of the observations. This value increases to 97% when central months are considered. In 1993 and 1994, the volcanic aerosol injected by the Mt. Pinatubo eruption in 1991 was still in the polar vortex. McMurdo has a favorable geographic position for mountain waves propagation to the stratosphere. A numerical methodology is used to discriminate PSCs formed in large scale low temperature fields (synoptic PSCs) or in local temperature perturbations originated by lee waves events (mesoscale PSCs). This approach aims to reveal the conditions driving PSCs formation and to comprehend the potential role of smallscale phenomena. Synoptic and mesoscale PSCs are analyzed and significant differences are observed between types occurring under different conditions. The seasonal evolution shows specific features in PSCs development for both categories, besides spatial and temporal differences between volcanic and post-volcanic period. The conditions driving solid PSC formation during the first part of the winter season are investigated using local temperatures by radiosondes and back-trajectory analysis. Some comparisons with satellite PSC data complete the climatology.