RAYLEIGH LIDAR OBSERVATIONS OF MESOSPHERE TEMPERATURE STRUCTURE

Ground-based observations of atmospheric density profiles to 92 km wer e obtained for four successive seasons between summer 1989 and spring 1990. These results were obtained with a powerful Rayleigh lidar facil ity located at Wright Patterson Air Force Base (Dayton, Ohio). This in strument combined a 14-W XeF laser transmitter with a 2.54-m receiver mirror to observe returns from altitudes between 40 and 95 km. Analysi s of the scale height dependence of the density profiles produced temp eratures with a measurement error of about 5 K (approximately 2.5%) at 90 km when the lidar data was averaged for 20 min. and smoothed in he ight over 2.7 km. Examination of these profiles for the total of 18 ni ghts showed that there often existed in the mesophere a layer of enhan ced temperatures when compared with the U.S. standard profile. The lay er centroid height was about 85 km for summer and 70 to 75 km for wint er. Data obtained for the equinoctial periods showed the amplitude of these layers to be weak. The winter temperature profiles showed eviden ce for long-period waves passing through the region of the thermal ano maly while the equinox profiles revealed more sporadic wave activity w ith shorter vertical wavelengths. Both the winter and summer temperatu re data displayed regions where the observed lapse rate approached the adiabatic lapse rate. In the summer the wave activity near the invers ion layer was weak.