Observational Evidence of Nonlinear Wave-Wave Interaction Over Antarctic MLT Region

Using meteor radar observations over King Sejong Station (62.22 degrees S, 58.78 degrees W) in the Antarctic Peninsula, we investigated the wave-wave interaction in the mesosphere and lower thermosphere (MLT) region. We analyzed hourly horizontal wind measurements at altitudes of 84-96 km from March 2016 through February 2017 and found that the MLT region is dominated by a semidiurnal tide (SDT) and the signature of planetary waves (PWs) with a period of similar to 8-27 days. The PW activity was substantially intensified during the winter. The day-to-day variability of SDT amplitudes are estimated and the higher-order spectral analysis of SDT amplitudes exhibits intermittent modulation of SDT at PW periods similar to 8 and 27 days in the zonal winds and periods of 8 and 16 days in the meridional winds. We observed an intense episode of tidal modulation from June through September 2016, during which a set of subsidiary spectral components around the SDT were found as a result of wave-wave interaction. Further, the bi-spectral analysis reveals that quadratic coupling (nonlinear interaction) occurred between SDT and PWs at a band period of 8-27 days, at above 90 km. We compared the spectral powers between the secondary waves created by the nonlinear interaction between the SDT and 16-day PWs. Further, we found that sum-secondary waves generated by the nonlinear interaction are stronger than the difference-secondary waves during austral winter 2016. We thus conclude that the non-linear interaction between the tides and PWs may play a major role in the short-term tidal variability in the MLT region during austral winter 2016.