Non-linear interactions between tides and planetary waves resulting in periodic tidal variability

Data obtained from a meteor radar at Sheffield, U.K. (53 degrees 27'N, 1 de grees 35'W) between 30 June 1989 and 6 October 1994 have been used to study the variability of tidal amplitudes and the possibility that this is cause d by non-linear interactions with planetary waves. Instances of regular var iations in tidal amplitude with periods corresponding to those of simultane ously-observed planetary waves are investigated. The observed tidal variabi lity is analysed in the light of a current theory of non-linear interaction between tides and planetary waves, which predicts the presence of secondar y waves having frequencies that are the sum and difference of the primary w aves involved in the interaction. Three case studies are presented in which periodogram analysis reveals the presence of these secondary waves and a b ispectral analysis of the same data is used to confirm these findings. The suitability and limitations of this latter technique as a detector of quadr atic phase coupling in data sets of the type used in this study are discuss ed. (C) 1999 Elsevier Science Ltd. All rights reserved.