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Ann. Geophys., 20, 2033-2038, 2002
www.ann-geophys.net/20/2033/2002/
© European Geosciences Union 2002
The 16-day variation in tidal amplitudes at Grahamstown (33.3° S, 26.5° E)
S. B. Malinga and L. M. G. Poole
Department of Physics and Electronics, Rhodes University, Grahamstown, 6140, South Africa
Correspondence to: L. M. G. Poole (g.poole@ru.ac.za)
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)
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