EVIDENCE FOR NONLINEAR COUPLING OF PLANETARY-WAVES AND TIDES IN THE ANTARCTIC MESOPAUSE

Analyses of hourly-mean meridional and zonal winds near 95 km, observe d with the meteor radar system at Molodezhnaya station (68 degrees S, 45 degrees E) during 1990, reveal the presence of long-period (2-18 da y) waves with dominant periods corresponding to those of Rossby normal modes modified by mean zonal winds. Time-varying analyses indicate th at although significant contributions at planetary wave periods persis t with nearly constant periods for intervals of days to weeks, tempora l variability of these periods is observed over longer intervals. Tida l motions, which mainly consist of the semidiurnal and the diurnal per iods, demonstrate considerable modulation of their amplitudes that var y with time. The observed tidal amplitude modulations are investigated through bispectral analyses. The results of these analyses suggest no nlinear interactions of quadratic form between oscillations with perio ds in the range of 2 to 19 days and the diurnal and semidiurnal tides at various intervals during 1990.