ANNUAL AND SEMIANNUAL TEMPERATURE OSCILLATIONS IN THE UPPER MESOSPHERE

Fourier transform spectrometer observations bf the mesosphere have bee n performed at the University of Michigan (latitude: 42 1/2 N) on a lo ng term basis. A database of near infrared Meinel hydroxyl spectra has been accumulated from which rotational temperatures have been determi ned. Harmonic analysis of one-day averaged temperatures for the period 1992.0 to 1994.5 has shown a distinct annual and semi-annual variatio n. Subsequent fitting of a five term periodic function characterizing the annual and semi-annual temperature oscillations to the daily avera ged temperatures was performed. The resultant mean temperature and the amplitudes and phases of the annual and semi-annual variations are sh own to coincide with an emission height slightly above 85 km which is consistent with the mean rocket derived altitude for peak nocturnal hy droxyl emission.