Quasi-biennial modulation of the semidiurnal tide in the upper mesosphere above Halley, Antarctica

We present an analysis of a long-term archive of horizontal wind data derived from meteor wind observations from a SuperDARN radar at Halley, Antarctica (76S, 27W). Systematic differences between the 12-hour component in the meridional wind and the climatological mean are observed showing evidence of a quasi-biennial modulation of the high-latitude semidiurnal tide in the upper mesosphere. The amplitude of the observed tides is enhanced when the equatorial stratospheric quasibiennial oscillation above 10 hPa is westerly. This enhancement is greatest in the summertime tidal amplitudes when the zonal wavenumber one (S = 1) nonmigrating component dominates the semidiurnal wind field, and is coincident with an enhancement of the summertime planetary wave activity in the upper mesosphere. These observations strongly support the hypothesis that the S = 1 component of the semidiurnal tide observed at high latitudes is due to a non-linear interaction between the migrating S = 2 semidiurnal tide and quasi-stationary S = 1 planetary waves.