Comparison of simultaneous Na lidar and mesospheric nightglow temperature measurements and the effects of tides on the emission layer heights

A detailed comparative study of two new mesospheric temperature data sets, measured by different remote- sensing techniques, has been performed as part of a longterm investigation of low- latitude mesospheric dynamics. Coincident observations using the University of Illinois Na wind/ temperature lidar and the Utah State University CEDAR Mesospheric Temperature Mapper ( MTM) were conducted from the summit of ;Haleakala Crater, Maui, Hawaii ( 20.8 degrees N, 156.2 degrees W, similar to 3000 m) as part of the Maui- MALT program. High- quality joint measurements were obtained during four lidar campaign periods, and 16 nights of data, spanning the interval January 2002 to October 2003, are presented here as example observations during each season. The Na lidar was coupled to the Air Force 3.7 m diameter steerable telescope providing exceptional quality temperature ( and wind) data spanning the altitude range similar to 80 - 105 km. At the same time the MTM sequentially sampled the NIR OH ( 6,2) Meinel band and the O-2 ( 0,1) Atmospheric band nightglow emissions to determine the height- weighted mesospheric temperature at two nominal altitudes within this region. Comparison of these two nocturnal data sets shows exceptionally good agreement on a point- to- point, as well as a nightly mean basis, especially when allowances were made for physically reasonable changes in height during the course of the night for each of the nightglow layers. This analysis yields mean nocturnal altitudes of 88.6 km with a nocturnal variability of +/- 3.0 km for the OH M ( 6,2) band emission layer and 94.4 km for the O2 ( 0,1) Atmospheric band mean altitude with a nocturnal variability of +/- 4.2 km. These results are in excellent accord with previous rocket, satellite and ground- based observations and further establish the validity of these two complementary measurement techniques. Furthermore, analysis of the computed height changes inferred from this study indicates a systematic decrease in altitude of both emission layers by up to several kilometers, whenever the lidar data showed evidence of strong diurnal or semidiurnal tidal forcing. The apparent downward trend in altitude was found to track the phase of the prevailing tidal motion providing new evidence for the effects of tides ( or long- period gravity waves) on the height variability of the nightglow layers.