We present an analysis of a long-term archive ofhorizontal wind data derived from meteor windobservations from a SuperDARN radar at Halley,Antarctica (76S, 27W). Systematic differences betweenthe 12-hour component in the meridional wind and theclimatological mean are observed showing evidence of aquasi-biennial modulation of the high-latitude semidiurnaltide in the upper mesosphere. The amplitude of the observedtides is enhanced when the equatorial stratospheric quasibiennialoscillation above 10 hPa is westerly. Thisenhancement is greatest in the summertime tidalamplitudes when the zonal wavenumber one (S = 1) nonmigratingcomponent dominates the semidiurnal wind field,and is coincident with an enhancement of the summertimeplanetary wave activity in the upper mesosphere. Theseobservations strongly support the hypothesis that the S = 1component of the semidiurnal tide observed at high latitudesis due to a non-linear interaction between the migrating S = 2semidiurnal tide and quasi-stationary S = 1 planetary waves.