Tidal modulation of the gravity‐wave momentum flux in the Antarctic mesosphere

Abstract

Airglow imager and dynasonde/IDI radar wind measurements at Halley Station, Antarctica (76°S, 27°W) have been used to estimate the diurnal variation of the vertical fluxes of horizontal momentum carried by high‐frequency atmospheric gravity waves. The cross‐correlation coefficients between the vertical and horizontal wind perturbations were calculated from the sodium airglow imager data collected during four consecutive nights of near total darkness during July of 2000. These were combined with wind‐velocity variances from coincident radar measurements to estimate the upper limit of the vertical flux of horizontal momentum during three‐hour intervals throughout the period. The resulting momentum flux showed a marked semi‐diurnal oscillation in the zonal and meridional components. Calculations of the momentum flux through the Na airglow show variations in period and phase consistent with the observations, implying that tidal propagation and modulated gravity‐wave forcing may both affect observed wind variations.

Gravity wave amplitudes and momentum fluxes inferred from OH airglow intensities and meteor radar winds during SpreadFEx

“…Figure 4b and e suggests a wave field that propagates to the opposite direction of the horizontal wind, which is consistent with the wind filtering theory (e.g. McLandress, 1998;Espy et al, 2004). While the modeled horizontal wind is northwest oriented, the flux of waves points in the opposite direction, which indicates wave blocking in that direction.…”

Seasonal variations of the vertical fluxes of heat and horizontal momentum in the mesopause region at Starfire Optical Range, New Mexico

“…The seasonal variation of the meridional momentum flux is therefore opposite to the variation of the meridional wind. This mean wind filtering effect is also evident in the seasonal variation of gravity wave directions observed by Nakamura et al [1999] at Shigaraki, Japan (35°N, 136°E) and momentum flux by Espy et al [2004a, 2004b] at Halley Station, Antarctica (75.6°S, 26.6°W).…”

Southern Argentina Agile Meteor Radar: Initial assessment of gravity wave momentum fluxes

“…Finally, we note that large local GW momentum flux estimates, either accompanying tidal modulation [ Fritts and Vincent , 1987; Wang and Fritts , 1991; Espy et al , 2004], arising from specific sources [ Espy et al , 2006; Smith et al , 2009], or having no identified cause [ Fritts et al , 2002] often occur in the MLT. These estimates can significantly exceed the mean values reported at various sites, occasionally by one or two decades.…”