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

Abstract

[1] 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°S, 68°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.

The diurnal and semidiurnal tides over Ascension Island (° S, 14° W) and their interaction with the stratospheric quasi-biennial oscillation: studies with meteor radar, eCMAM and WACCM

“…The wind and temperature perturbations of tides can act to filter the field of ascending gravity waves and so modulate gravity-wave fluxes of energy and momentum (e.g. Fritts and Vincent, 1987;Beldon and Mitchell, 2010). Non-linear interactions between tides and planetary waves can generate planetary-scale secondary waves which are thought to play a key role in tidal variability and impose a modulation on tidal amplitudes at planetary-wave periods (e.g.…”

Frequency variations of gravity waves interacting with a time-varying tide

“…Tides are believed to strongly modulate the propagation conditions experienced by upward-propagating GWs (Beldon and Mitchell, 2010). In the context of energy conservation, tidal and GW amplitudes grow with increasing altitude because of the exponentially decreasing atmospheric density with height.…”

“…There is considerable observational evidence of strong tidal-GW interactions in the middle and upper atmosphere (Thayaparan et al, 1995;Isler and Fritts, 1996;Nakamura et al, 1997;Manson et al, 1998;Meriwether et al, 1998;Sica et al, 2002;Williams et al, 2006;Sridharan et al, 2008;Beldon and Mitchell, 2010;Huang et al, 2012). In addition to observational studies, numerical models have been employed extensively to study tidal-GW interactions (Forbes et al, 1991;McLandress and Ward, 1994;Eckermann and Marks, 1996;Liu and Hagan, 1998;Mayr et al, 1998Mayr et al, , 2001Meyer, 1999;Norton and Thuburn, 1999;Liu et al, 2000;Akmaev, 2001;England et al, 2006;Ortland and Alexander, 2006;Liu et al, 2008;Senf and Achatz, 2011).…”

“…In addition to observational studies, numerical models have been employed extensively to study tidal-GW interactions (Forbes et al, 1991;McLandress and Ward, 1994;Eckermann and Marks, 1996;Liu and Hagan, 1998;Mayr et al, 1998Mayr et al, , 2001Meyer, 1999;Norton and Thuburn, 1999;Liu et al, 2000;Akmaev, 2001;England et al, 2006;Ortland and Alexander, 2006;Liu et al, 2008;Senf and Achatz, 2011). Based on these observational and numerical studies, we know that tidal-GW interactions can, among others, (1) change the local wind and temperature, e.g., by forming temperatureinversion layers (Liu and Hagan, 1998;Meriwether et al, 1998;Sica et al, 2002;Sridharan et al, 2008); (2) cause short-term and seasonal variability of tidal structures (Mayr et al, 1998;Meyer, 1999); (3) modulate GWs' energy and momentum flux (Beldon and Mitchell, 2010); and (4) lead to GW instability and dissipation at the critical layers (Williams et al, 2006).…”

Diurnal variation in gravity wave activity at low and middle latitudes

“…Studies of GW variances or momentum fluxes to date have addressed primarily seasonal variations (e.g., Antonita et al, 2008;Beldon and Mitchell, 2010;Fritts et al, 2010Fritts et al, , 2012aPlacke et al, 2011a), most using the Hocking (2005) analysis method or a derivative thereof. The Hocking (2005) method in principle allows the use of meteor radar data to estimate the large-scale motions as well as all GW variances and momentum fluxes.…”