Characteristics of atmospheric waves in the tidal period range derived from zenith observations of O2(0–1) Atmospheric and OH(6‐2) airglow at lower midlatitudes

Abstract

From about 100 nights of ground‐based measurements of fluctuations in airglow brightness and rotational temperature, taken from two sites at 32°S and 37°N, a considerable number of new determinations of complex values of Krassovsky's η are derived, and compared with observations by other investigators and model predictions. Our findings support the model of Hines, Tarasick, and Shepherd (HTS), which leads to practical consequences regarding the usefulness of airglow observations for deriving vertical propagation of atmospheric waves in the mesopause region. It is shown, at least in part, that the vertical wave propagation can be inferred from zenith observations of one airglow emission, alone, and that consistent information can be obtained simultaneously for the two airglow layers. The analysis presented comprises the range of observed periods between 3 and 24 hours. The salient feature is that η values are essentially limited to the fourth quadrant, for both the O2 and OH emissions, which means, according to the HTS model, that the majority of the waves observed propagate upward, with vertical wavelengths between 20 and 60 km, and only a few are possibly evanescent. This would not contradict the interpretation that most if not all of the wave signatures may be due to the semidiurnal tide, or tidal transients.