Climatology of a midlatitude mesopause region observed by a lidar at Fort Collins, Colorado (40.6°N, 105°W)

On the basis of 147 nights of quality lidar data over a period of 3 years the thermal structure of the mesopause region over Fort Collins, Colorado (40.6°N, 105°W), has been constructed. False color contour plots depicting seasonal temperature variations are given. Monthly mean temperatures between 81 and 105 km are tabulated, from which a cool mean summer mesopause of 178 K at 86 km and a warm mean winter mesopause of 195 K at 101 km are determined. The mean temperature profiles exhibit double temperature minima in the mesopause region in spring and fall, but they are less obvious in summer and winter. Seasonal variations of the associated temperature maximum show a minimum in temperature (196 K) and a maximum in altitude (95 km) a month before summer solstice. These results elucidate the heating mechanisms in the mesopause region. Harmonic analysis of the temperature profiles identifies a node at 99 km in the annual amplitude, below which point an out-of-phase evolution between temperature and mean solar flux forcing is observed, suggesting a dynamics-dominated mesopause.