Comparison of terdiurnal tidal oscillations in mesospheric OH rotational temperature and Na lidar temperature measurements at mid-latitudes for fall/spring conditions

Results from two different instrumental techniques, an Na Wind/Temperature Lidar and an OH Mesospheric Temperature Mapper, have been combined to inves tigate the occurrence and properties of the mid-latitude terdiurnal (8-hr) tide at near mesopause attitudes (80-105 km). High-resolution Na lidar meas urements were taken throughout the diurnal and annual cycle (1996-98) at Ur bana, Illinois (40 degrees N, 88 degrees W) to characterize the seasonal be havior of the 24, 12, 8 and 6-hr tides. Complementary measurements using a recently developed CCD imager capable of mapping OH temperature (at similar to 87 km altitude) were made from Bear Lake Observatory, Utah (41.9 degree s N, 111.6 degrees W) and Ft. Collins, Colorado(40.6 degrees N, 105 degrees W) within the same time period. The "mean day" lidar data for the spring a nd fall periods investigated here each indicate an average amplitude variat ion of similar to 2-5 K over the depth of the OH layer but distinct phases of <1-hr LST and similar to 7-hr LST respectively, for the 8-hr component. The Temperature Mapper data are in excellent agreement with these findings but in addition have shown that the amplitude of this tidal component can v ary by as much as an order of magnitude (1.5-15 K) on a night-by-night basi s resulting in an apparent 8-hr dominance of the nocturnal variation during investigated portions of the spring and fall seasons with little or no diu rnal and semi-diurnal variability evident. Reports of terdiurnal tidal meas urements in the mid-latitude nightglow emissions are exceptionally rare and have yet to be modeled. These innovative joint measurements pave the way f or new research in this important area.