Abstract

Spectra of the Meinel hydroxyl emissions in the wavelength range LO-l.6 um, which originate at altitudes close to the mesopause, have been obtained, using a Fourier transform spectrometer at Maynooth (53.23°N, 6.35*W), Ireland, on all suitable nights during the period December 1992 to July 1995. Rotational temperatures and integrated band intensities have been calculated from the spectra of the OH (3, 1) vibrational band. These data have been analysed for evidence of tidal activity. Our results show a post sunset increase in the emission brightness throughout the year; over 70% of the time this is followed by a decline to a midnight minimum, after which the emission rate recovers to a secondary maximum in the early morning. The months of September and October show a completely different pattern with the intensity and temperature data showing a pre-midnight maximum followed by a steady decline until dawn. A cross-correlation of the intensity and temperature data reveals a periodic variation with a period in the range 8-12 hours for all months.