Lidar observations of polar mesospheric clouds at South Pole: Diurnal variations

Polar mesospheric clouds (PMCs) were observed by a ground-based Fe Boltzman n temperature lidar for 65 h on 17-19 and 24-26 January 2000 above the geog raphic South Pole. The mean PMC backscatter ratio, volume backscatter coeff icient, total backscatter coefficient, layer centroid altitude, and laser r ms width are 53.5, 2.9x10(-9) m(-1) sr(-1), 4.3x10(-6) sr(-1), 85.37 km, an d 0.78 km, respectively. Strong semidiurnal and diurnal oscillations were o bserved in the PMC backscatter ratio, volume backscatter coefficient, total backscatter coefficient, and centroid altitude. The oscillations are all m aximum around 0630 and 1900 UT. The variations appear to be linked to verti cal advection of the PMC scattering layers by a persistent oscillation in t he vertical wind velocity. Scattering is strongest when the PMCs are highes t which suggests that the colder temperatures at higher altitudes near the mesopause facilitate the formation of larger PMC particles.