Interannual variability of the S=1 and S=2 components of the semidiurnal tide in the Antarctic MLT

Twelve years of horizontal wind data from the Scott Base MF radar and the Halley SuperDARN radar recorded between January 1996 and December 2007 are analysed to study the interannual variability of the migrating (S¼2) and non-migrating (S¼1) components of the semidiurnal tide around 781S in the Antarctic upper mesosphere. Significant quasi-biennial modulation of the summer time S¼1 component is observed. During early summer the amplitude of the component is up to 4 ms1 stronger during the easterly phase of the equatorial stratospheric quasi-biennial oscillation (QBO) measured at 30 hPa. No statistically significant effect is seen in amplitude of the migrating component of the tide, or in the phase (time of maximum) of either component. These results are discussed in the light of previous observations of the interannual variability of the semidiurnal tide.