Mesopause-region tidal variability observed by meteor radar

Observations of mesopause-region neutral winds made by a meteor-radar at Sheffield (53 degrees 27'N, 1 degrees 35'W) have been used to study the short-term variability of the velocity amplitudes of the terdiurnal, semidiurnal, and diurnal tides during the summer of 1993. Modulation of the amplitudes of the latter two tides is observed in July. The period of modulation of the semidiurnal tide corresponds to that of the quasi-two-day planetary wave which was observed contemporaneously. A local non-linear interaction is suggested by the presence of the modulated tide, the quasi-two-day-wave and "frequency sum and difference" secondary waves. (C) 1997 COSPAR. Published by Elsevier Science Ltd.