Seasonal variability in mesopause region temperatures over Fort Collins, CO (41°N, 105°W) based on lidar observations, 1990 through 2007

Nearly 900 nocturnal temperature profiles (85-105 km) from the Colorado State University Na lidar at Fort Collins, CO (40.59N, 105.14W) from 1990 to 2007. After the removal of an episodic warming attributable to Mt. Pinatubo eruption, the time series is analyzed as the sum of the climatological mean, annual and semiannual oscillation, solar cycle effect and trends along with possible annual/semiannual modulation of the latter two. The direct seasonal variation is consistent with the concept of the two-level mesopause. The trends in summer and winter are comparable 90-96 km at ∼−0.15±0.1 K/year. The summer trend turns positive above 96 km. The winter trend is negative with minimum of ∼−0.3 K/year at ∼100 km but positive at ∼104 km. The negative trend values are a factor of five smaller than an earlier analysis of the early part of this data due to removal of an episodic event.