Abstract
Abstract. Meteor wind data at Grahamstown (33.3° S, 26.5° E) have been used to study the short-term (planetary scale) variations of the diurnal and semidiurnal tidal amplitudes at ~ 90 km altitude. Wavelet multi-resolution and spectral techniques reveal that planetary periodicities of ~ 10 and ~ 16 days dominate the wave spectrum in the ~ 2–20-day period range. The quasi-16-day oscillation is thought to be related to similar oscillations in the lower atmosphere. Also, there seems to be a link between the winter/equinox 16-day oscillation in the mean flow and that in the semidiurnal tidal amplitudes. It is thought that this is probably due to either the coupling between the normal mode-mean flow interactions and the gravity wave-tidal interactions, or to direct nonlinear interactions between planetary waves and the tide. On the other hand, a comparison of the mean flow and the diurnal tide does not show evidence of correlation. Possible reasons for this disparity are discussed briefly.Key words. Meteorology and atmospheric dynamics (waves and tides)
Highlights
In an earlier paper (Malinga and Poole, 2002, which will be referred to as Paper 1), we considered the short-term variations of the mean flow with special emphasis on the quasi16-day oscillation
In this paper we study similar variations in the diurnal and semidiurnal tidal amplitudes
Question that comes to mind is whether the 16-day oscillation in the tidal amplitudes is related to that in the mean flow or not. Such a link could be due to the coupling between the normal mode-mean flow interactions (Paper 1) and gravity wave-tidal interactions
Summary
In an earlier paper (Malinga and Poole, 2002, which will be referred to as Paper 1), we considered the short-term variations of the mean flow with special emphasis on the quasi16-day oscillation. These authors concluded that whether gravity wave forcing results in amplitude decreases (e.g. Fritts and Vincent, 1987; Forbes et al, 1991) or increases (e.g. Wang and Fritts, 1991) depends on the details of the tidally modulated filtering of gravity waves.
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