Abstract
Nonlinear interactions among gravity waves and among tides and planetary waves (PWs) have extensively been studied, however, resonant interactions between tides and annual (AO) and semiannual (SAO) oscillations were not reported. By using meteor radar observations and reanalysis data for 9 years, we demonstrate that the sum and difference resonant interactions between the diurnal (DT)/semidiurnal (SDT) tides and the AO/SAO do occur in the mesosphere and lower thermosphere (MLT). Both the frequencies and wavenumbers of the secondary waves in the sum (difference) resonant interactions just equal the sum (difference) frequencies and wavenumbers between the DT/SDT and the AO/SAO. Spectral analysis shows that only the DT, SDT, AO, SAO and their secondary waves are the predominant components in both the zonal and meridional winds at 90 km with the spectral amplitudes of 3.5–17.7 ms-1, being much stronger than all the other spectral amplitudes, including the amplitudes (2.1–2.2 ms-1) of the relatively strong terdiurnal tide and 16-day PW. At some altitudes in the MLT, the secondary waves are more intense than the DT/SDT, thus in tidal studies, the magnitude of the secondary waves may be regarded as the tidal one if the observational period is not long enough or their spectral peaks are not distinguished carefully.
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