Polar mesospheric clouds at the South Pole

We made the first lidar observations of polar mesospheric clouds (PMC) at the South Pole and in the southern hemisphere with an Fe Boltzmann temperature lidar in the 1999-2000 and 2000-2001 austral summer seasons. Strong PMC activities were observed at the South Pole and extensive data were collected. Here we summarize the lidar observation results including the interannual, seasonal and diurnal variations of PMC altitude, brightness and occurrence probability. In particular, our data show that PMC at the South Pole are a few kilometers higher than in the northern hemisphere and PMC at the South Pole exhibit seasonal trends in both altitude and brightness. We explore the possible causes through the study of atmospheric thermal structure and upwelling wind by using NCAR TIME-GCM model and then presenting a PMC altitude model. Our initial conclusion is that these hemispheric differences and seasonal trends in PMC altitudes are the combination results of the hemispheric differences in thermal structure and upwelling wind, which are caused by the Earth orbital eccentricity and inter-hemisphere difference in gravity wave forcing.