Lidar Measurements of the MLT Thermal Structure At Maui, HI (20.7çN) And Starfire Optical Range, NM (35çN)

The University of Illinois Na wind/temperature lidar was coupled to large astronomical telescopes at the Starfire Optical Range (SOR) in Albuquerque, New Mexico (35.0çN, 106.5çW), and at the Maui Space Surveillance Complex on the top of the Haleakala in Maui, Hawaii (20.7çN, 156.3çW). Hundreds of hours of high-quality temperature and wind data have been collected at these two locations. This provided us a good opportunity to study the subtropical thermal structure of the mesosphere and lower thermosphere (MLT) region, and make comparisons with mid-latitudes. We also compared the observations with the MSIS-00 model. Both locations exhibit mesospheric temperature inversion layers (MIL) between 85 and 100 km, which are not predicted by the MSIS-00 model. The amplitudes of the Maui MILs are about half of those at SOR and the Maui MILs have a smaller width compared to the SOR MILs. The Maui lidar temperatures are generally warmer than the MSIS-00 predictions, while the SOR lidar data are comparable to the MSIS-00 except in the MIL altitude range. Both SOR and Maui mesopause temperatures are coldest in mid-summer and warmest during the mesopause transition periods. However, the Maui mesopause is warmer than the SOR, and the amplitude of the mesopause temperature variations at Maui is much smaller than at SOR. Two distinct levels of mesopause altitudes are clearly shown in the SOR seasonal data with a low altitude around 86.5 km in summer (May through August) and a high altitude around 101 km during the rest of the year. Abrupt transitions between the two stable levels occur in early May and early September. At Maui, the lidar measurements indicate a low mesopause altitude near 87.5 km in July when averaging over a 10-h period centered at local midnight. Tides strongly influence the MLT temperature and the mesopause structure. The composite night in July shows that the lowest temperature is near 87.5 km at the beginning of the night and then switches to a higher altitude around 100 km after local midnight. With the semi-diurnal tides removed from the data, the composite night indicates that the mesopause stays at the low altitude through most of the night in July at Maui.