Interannual and Diurnal Variability of PMCs Using 10 years of Lidar and 14 years of CIPS Observations at McMurdo, Antarctica

Polar mesospheric clouds (PMCs) are important tracers of the mesosphere and lower
thermosphere (MLT); thus, it is vital to characterize them and understand their long-term trends
and causes of their variability. This study aims to characterize PMCs at McMurdo and address
the dynamical factors that contribute to PMC interannual and diurnal variability. Over 939 hours
of PMCs have been detected using a ground-based Fe Boltzmann lidar, with an occurrence rate
of 30.8% during the austral summer seasons from Dec 2010 to Feb 2020.  The mean centroid
altitude of these clouds in the last 10 years is 84.35 ± 0.04 km with the average total backscatter
coefficient of 4.96 ± 0.095  10 -6 sr -1 These results verify the previous studies on latitudinal
dependence of PMCs. On comparing the 10 years of lidar PMC observations with PMCs
observed by CIPS onboard NASA’s AIM satellite, strong correlations are seen between lidar
PMC brightness and CIPS PMC albedo. 

Using stratospheric wind reversal dates as a proxy for polar vortex break-up timing, a strong
correlation of R= -0.63 with a confidence level of 98.1%, is observed between PMC albedo and
wind reversal dates. Thus, late polar vortex break-up timing leads to a weak, less bright PMC
season. When the effect of solar flux, is combined with wind reversal dates, the correlation
further increases by 0.12, with R = -0.75 with a confidence level of 99.7%. Our results conclude
that the dynamical forcing of the polar vortex overshadows the radiative forcing, causing the
solar cycle to take a back seat in driving PMC interannual variability. Finally, this study shows
that the diurnal variability of Lidar PMC brightness over the 10 years has a time lag correlation
with meridional winds, indicating the role of upwelling winds in PMC formation.