Mesospheric temperature inversions observed from long-term lidar measurements at mid and low latitudes

Abstract

Results from new observations of mesospheric temperature inversion layers using long-term lidar measurements at mid- and low-latitudes are presented. Observations of inversions above Table Mountain, California, (34.4 degrees N) and Mauna Loa, Hawaii, (19.5 degrees N) are in very good agreement with previous lidar and satellite observations. At least two distinct types of events have been observed. The winter inversions occur near 70 km altitude at midlatitudes in December-January and about 1 - 2 months laster at subtropical latitudes. The tidal signature in the middle atmospheric thermal structure has been investigated using more than 140 hours of nighttime lidar measurements at TMF during January 1997 and February 1998. The temperature profiles (30 - 85 km) revealed the presence of persistent mesospheric inversions around 65 - 70 km altitude with a clear Local-Solar-Time (LST) dependence. Also, some higher altitude inversions (80 - 85 km) have been observed at lower latitudes around the equinoxes and 1 - 2 months later at mid-latitudes. In particular the temperature minimum systematically observed at the altitude of approximately 80 km and propagating downward throughout the night might also suggest the important role played by the tides.