Tidal variations of O₂ Atmospheric and OH(6-2) airglow and temperature at mid-latitudes from SATI observations

Abstract

Airglow observations with a Spectral Airglow Temperature Imager (SATI), installed at the Sierra Nevada Observatory (37.06° N, 3.38° W) at 2900-m height, have been used to investigate the presence of tidal variations at mid-latitudes in the mesosphere/lower thermosphere region. Diurnal variations of the column emission rate and vertically averaged temperature of the O2 Atmospheric (0-1) band and of the OH Meinel (6-2) band from 5 years (1998-2003) of observations have been analysed. From these observations a clear tidal variation of both emission rates and rotational temperatures is inferred. It is found that the amplitude of the daily variation for both emission rates and temperatures is greater from late autumn to spring than during summer. The amplitude decreases by more than a factor of two during summer and early autumn with respect to the amplitude in the winter-spring months. Although the tidal modulations are preferentially semidiurnal in both rotational temperatures and emission rates during the whole year, during early spring the tidal modulations seem to be more consistent with a diurnal modulation in both rotational temperatures and emission rates. Moreover, the OH emission rate from late autumn to early winter has a pattern suggesting both diurnal and semidiurnal tidal modulations.