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

Polar mesospheric clouds (PMCs) were observed by a ground-based Fe Boltzmann temperature lidar for 65 h on 17-19 and 24-26 January 2000 above the geographic South Pole. The mean PMC backscatter ratio, volume backscatter coefficient, total backscatter coefficient, layer centroid altitude, and layer rms width are 53.5, 2.9×10^-9 m^-1sr^-1, 4.3×10⁶ sr^-1, 85.37 km, and 0.78 km, respectively. Strong semidiurnal and diurnal oscillations were observed in the PMC backscatter ratio, volume backscatter coefficient, total backscatter coefficient, and centroid altitude. The oscillations are all maximum around 0630 and 1900 UT. The variations appear to be linked to vertical advection of the PMC scattering layers by a persistent oscillation in the vertical wind velocity. Scattering is strongest when the PMCs are highest which suggests that the colder temperatures at higher altitudes near the mesopause facilitate the formation of larger PMC particles.