Quasi-2-day wave and tidal variability observed over Ascension Island during January/February 2003

The tidal variability observed in the equatorial mesosphere–lower thermosphere (MLT) region over Ascension Island at a time when a very large quasi-2-day wave was present (January/February 2003) has been investigated. The results indicate that two different types of variability of the diurnal tide were present: (i) a change of the diurnal tidal mode when the period of the 2-day wave was very close to 48 h and the amplitudes were very large, and (ii) a 2-day wave/tidal coupling when the period of the 2-day wave was different from 48 h, the phases were stable, and the amplitudes were not so large as in the previous case. A secondary wave analysis was performed to prove the frequency and vertical wavenumber (wavelength) relationship between the primary and the secondary waves. A cross-correlation analysis between the amplitudes of the primary and secondary waves shed some light on the source of energy for the secondary waves.