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.