Gravity wave-tidal interactions in the mesosphere and lower thermosphere over Rothera, Antarctica (68 degrees S, 68 degrees W)

A simple technique for measuring gravity wave activity has been used to investigate gravity wave-tidal interactions in the polar mesosphere and lower thermosphere (MLT). The technique uses the radial velocities of individual meteors recorded by meteor radar to derive a statistical measure (variance) of the activity of the high-frequency gravity wave field. This technique can measure gravity waves with horizontal wavelengths of up to about 400 km and periods up to approximately 3 hours. Interactions between the observed gravity wave field and the background wind are investigated using data collected between February 2005 and December 2008 by a meteor radar based at Rothera, Antarctica (68 degrees S, 68 degrees W). The results reveal the presence of significant modulations of the observed gravity wave field at tidal periods of 12 and 24 hours. Correlations between the hourly zonal winds and the gravity wave field measured by the meteor radar reveal an in-phase relationship between the hourly zonal winds and gravity wave variance in winter and an anti-phase relationship in summer. This is consistent with the theory of filtering by tidal winds acting on a zonally-asymmetric gravity wave field in which westward waves dominate in winter and eastward waves dominate in summer. The limitations of the technique and the effect this has on the interpretation of these results are also considered. The effects of the diurnal cycles in meteor count rates, the uncertainty in recorded radial velocities and the uncertainty in the measured heights of meteors are considered.