The research activity under this proposal will consist of a combination of theoretical modeling and data analysis. Its primary objective is to gain an increased understanding of the energetics and dynamics of the atmospheric region situated between heights of 50 and 100 km. It will consist of an indepth study of Polar Mesospheric Clouds (PMC), a phenomenon which is a prominent manifestation of the energetics and dynamics in the summertime polar mesopause region near 84 km height. New modeling techniques which we have previously developed for simulating PMC evolution and optical properties will be combined with existing dynamical-photochemical models for the thermal and compositional structure of this atmospheric region. Newly- available satellite measurements of atmospheric properties will be used to develop a diagnostic model of the region's thermal, dynamical and transport processes. A second objective will be to determine the extent to which long-term anthropogenic changes in chemical composition of the lower atmosphere has impacted the thermal and dynamical structure of this region. In particular, we will develop both empirical and first-principles modeling methods to support our recent hypothesis that PMC is a relatively recent phenomenon, an indirect result of rising levels of tropospheric methane.
