CLIMATOLOGY OF A MIDLATITUDE MESOPAUSE REGION OBSERVED BY A LIDAR AT FORT-COLLINS, COLORADO (40.6-DEGREES-N, 105-DEGREES-W)

On the basis of 147 nights of quality lidar data over a period of 3 ye ars the thermal structure of the mesopause region over Fort Collins, C olorado (40.6 degrees N, 105 degrees W), has been constructed. False c olor 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 w inter mesopause of 195 K at 101 km are determined. The mean temperatur e profiles exhibit double temperature minima in the mesopause region i n spring and fall, but they are less obvious in summer and winter. Sea sonal variations of the associated temperature maximum show a minimum in temperature (196 K) and a maximum in altitude (95 km) a month befor e summer solstice. These results elucidate the heating mechanisms in t he mesopause region. Harmonic analysis of the temperature profiles ide ntifies 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.