Evidence for nonlinear coupling of planetary waves and tides in the Antarctic mesopause

Analyses of hourly-mean meridional and zonal winds near 95 km, observed with the meteor radar system at Molodezhnaya station (68 degrees S, 45 degrees E) during 1990, reveal the presence of long-period (2-18 day) waves with dominant periods corresponding to those of Rossby normal modes modified by mean zonal winds. Time-varying analyses indicate that although significant contributions at planetary wave periods persist with nearly constant periods for intervals of days to weeks, temporal variability of these periods is observed over longer intervals. Tidal motions, which mainly consist of the semidiurnal and the diurnal periods, demonstrate considerable modulation of their amplitudes that vary with time. The observed tidal amplitude modulations are investigated through bispectral analyses. The results of these analyses suggest nonlinear interactions of quadratic form between oscillations with periods in the range of 2 to 19 days and the diurnal and semidiurnal tides at various intervals during 1990.