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Ann. Geophys., 24, 81-88, 2006
www.ann-geophys.net/24/81/2006/
© European Geosciences Union 2006
Regional variations of mesospheric gravity-wave momentum flux over Antarctica
P. J. Espy1, R. E. Hibbins1, G. R. Swenson2, J. Tang2, M. J. Taylor3, D. M. Riggin4, and D. C. Fritts4
1The British Antarctic Survey, NERC, Cambridge, UK
2Department of Electrical & Computer Engineering, University of Illinois at Urbana-Champaign, USA
3Department of Physics, Utah State University, Logan, Utah, USA
4Colorado Research Associates, a division of NorthWest Research Associates, Boulder, Colorado, USA
Abstract. Images of mesospheric airglow and radar-wind measurements have been combined
to estimate the difference in the vertical flux of horizontal momentum
carried by high-frequency gravity waves over two dissimilar Antarctic
stations. Rothera (67° S, 68° W) is situated in the mountains of the
Peninsula near the edge of the wintertime polar vortex. In contrast, Halley
(76° S, 27° W), some 1658 km to the southeast, is located on an ice
sheet at the edge of the Antarctic Plateau and deep within the polar vortex
during winter. The cross-correlation coefficients between the vertical and
horizontal wind perturbations were calculated from sodium (Na) airglow
imager data collected during the austral winter seasons of 2002 and 2003 at
Rothera for comparison with the 2000 and 2001 results from Halley reported
previously (Espy et al., 2004). These cross-correlation coefficients were combined with
wind-velocity variances from coincident radar measurements to estimate the
daily averaged upper-limit of the vertical flux of horizontal momentum due
to gravity waves near the peak emission altitude of the Na nightglow layer,
90km. The resulting momentum flux at both stations displayed a large
day-to-day variability and showed a marked seasonal rotation from the
northwest to the southwest throughout the winter. However, the magnitude of
the flux at Rothera was about 4 times larger than that at Halley, suggesting
that the differences in the gravity-wave source functions and filtering by
the underlying winds at the two stations create significant regional
differences in wave forcing on the scale of the station separation.
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