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

A meteor radar has been used to measure horizontal winds during 1992 and 1993 in the mesosphere/lower‐thermosphere region over the England at 54.5°N, 3.9°W. Evidence is found of quasi‐periodic modulation of the amplitudes of planetary waves. Bispectral analysis applied to the data reveals a wealth of interactions occurring between different members of the population of planetary waves. The results of the bispectral analysis strongly support the idea that the mechanism of interaction is the quadratic nonlinear process proposed by Teitelbaum and Vial [1991] to account for tidal/planetary‐wave interactions. The interactions are strongest in summer between the 2‐day wave and waves with periods of about 10 and about 16 days. A number of secondary waves are produced in the interactions, and these could explain the apparent splitting of the 2‐day wave into a number of closely spaced frequencies. Considerable interannual variability in the waves and interactions is evident.