Terdiurnal oscillations in OH Meinel rotational temperatures for fall conditions at northern mid‐latitude sites

High‐precision (∼0.5 K) measurements of OH Meinel (M) (6,2) rotational temperatures above the Bear Lake Observatory, UT (42°N, 112°W) during October 1996 have revealed an interesting and unexpected mean nocturnal pattern. Ten quality nights (>100 h) of data have been used to form a mean night for autumnal, near‐equinoctial conditions. The mean temperature and RMS variability associated with this mean night were 203 ± 5 K and 2.4 K, respectively, and compare very favorably with expectations based on Na‐lidar measurements of mean tidal temperature perturbations over Urbana, IL (40°N, 88°W) during the fall 1996. Furthermore, this comparison shows that the 8‐h tide was the dominant source of the mean nocturnal temperature variability in the OH M region during this period. Additional data, obtained at Fort Collins, CO (41°N, 105°W) in November 1997, illustrate the occurrence of an 8‐h component of OH temperature variability about two months after the equinox and show that daily amplitudes as high as ≅15 K are possible.