Quasi-biennial oscillation influence on long-period planetary waves in the Antarctic upper mesosphere

Long-period planetary wave data derived from meteor wind observations recorded over a 12-year period with the SuperDARN radar at Halley, Antarctica, are presented and compared with the phase of the quasi-biennial oscillation (QBO) throughout the equatorial stratosphere. Enhanced planetary wave activity in the Antarctic upper mesosphere is found during the summer months, when the QBO in the equatorial upper stratosphere is westerly, and during the late winter, when the QBO in the upper stratosphere is easterly. These quasi-biennial enhancements in planetary wave activity coincide with a reduction in strength, by up to 30%, of the late-winter eastward winds in the Antarctic upper mesosphere. In addition, when the QBO is in the correct phase for enhanced planetary wave activity in the upper mesosphere above Halley, planetary wave activity measured in the upper mesosphere of the high-latitude Northern Hemisphere is reduced (and vice versa). These results clearly indicate significant interhemispheric propagation of planetary waves from the winter to summer hemispheres. Observational evidence that the stratospheric QBO induces a strong enough QBO in the equatorial upper mesosphere to act as a gate to the interhemispheric propagation of these long-period waves is discussed in light of these results.