Nonlinear interactions between planetary waves in the mesosphere/lower-thermosphere region

A meteor radar has been used to measure horizontal winds during 1992 and 19 93 in the mesosphere/lower-thermosphere region over the England at 54.5 deg rees N, 3.9 degrees W. Evidence is found of quasi-periodic modulation of th e amplitudes of planetary waves. Bispectral analysis applied to the data re veals a wealth of interactions occurring between different members of the p opulation of planetary waves. The results of the bispectral analysis strong ly support the idea that the mechanism of interaction is the quadratic nonl inear process proposed by Teitelbaum and Vial [1991] to account for tidal/p lanetary-wave interactions. The interactions are strongest in summer betwee n the 2-day wave and waves with periods of about 10 and about 16 days. A nu mber of secondary waves are produced in the interactions, and these could e xplain the apparent splitting of the 2-day wave into a number of closely sp aced frequencies. Considerable interannual variability in the waves and int eractions is evident.