Polar mesospheric clouds (PMC) are thin layers of water ice particles that form at high latitudes in the mesopause region (~85km). These clouds occur in both hemispheres during the respective summer seasons when the temperatures fall below 150 K. PMC are of particular interest as they directly reflect the presence of water vapor and temperature change in the middle-upper atmosphere, thus representing an important tool for the monitoring of climate change. The Fe Boltzmann temperature lidar, located at McMurdo and run by the University of Colorado Boulder, has continuously been operating since December 2010 at Arrival Heights near McMurdo, Antarctica. The lidar provided multiple years of PMC measurements, which allow one to effectively monitor the occurrence and the main characteristics of PMC.

The purpose of this study is to analyze seven seasons (2010-2017) of polar mesospheric clouds during the months of November, December, January and February. The research focuses on the hourly mean profiles of backscatter ratio R(z), volume backscatter coefficient beta(z), total backscatter coefficient beta_Total(z), centroid altitude Z_C and the RMS width. In order to improve the accuracy of the study, a method of data screening has been implemented. By comparing the signal to noise ratios integrated at Rayleigh altitude (30-45 km), it was possible to notice that generally anything with SNR < 8 had to be excluded from the data sets. This screening resulted in much clearer 374 nm and 372 nm Fe layer and PMC contours, which therefore facilitated the recognition of PMC. After plotting histograms of the aforementioned hourly parameters for each season, the study compares seasonal means, seasonal variations, and diurnal variations in order to characterize the PMC properties at this important high southern latitude. The preliminary results confirm the findings by Chu et al. [GRL, 2011] that the mean PMC centroid altitude is ~84.6 km, in between the altitudes at the South Pole and Rothera stations. Furthermore, the seven seasons of data clearly exhibit an anti-correlation between the total backscatter coefficient and centroid altitude. Our further analysis will reveal the diurnal variations in addition to the seasonal and inter-annual variations.