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 investigate the occurrence and properties of the mid-latitude terdiurnal (8-hr) tide at near mesopause altitudes (80-105 km). High-resolution Na lidar measurements were taken throughout the diurnal and annual cycle (1996-98) at Urbana, Illinois (40° N, 88° W) to characterize the seasonal behavior of the 24, 12, 8 and 6-hr tides. Complementary measurements using a recently developed CCD imager capable of mapping OH temperature (at~87 km altitude) were made from Bear Lake Observatory, Utah(41.9° N, 111.6° W) and Ft. Collins, Colorado (40.6° N, 105° W) within the same time period. The mean day lidar data for the spring and fall periods investigated here each indicate an average amplitude variation of~2-5 K over the depth of the OH layer but distinct phases of < 1-hr LST and~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 vary by as much as an order of magnitude (1.5-15 K) on a night-by-night basis resulting in an apparent 8-hr dominance of the nocturnal variation during investigated portions of the spring and fall seasons with little or no diurnal and semi-diurnal variability evident. Reports of terdiurnal tidal measurements in the mid-latitude nightglow emissions are exceptionally rare and have yet to be modeled. These innovative joint measurements pave the way for new research in this important area.