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Ann. Geophys., 24, 1199-1208, 2006
www.ann-geophys.net/24/1199/2006/
© European Geosciences Union 2006
Gravity wave propagation through a large semidiurnal tide and instabilities in the mesosphere and lower thermosphere during the winter 2003 MaCWAVE rocket campaign
B. P. Williams1, D. C. Fritts1, C. Y. She2, and R. A. Goldberg3
1Northwest Research Associates, Colorado Research Associates division, Boulder, Colorado, USA
2Department of Physics, Colorado State University, Fort Collins, Colorado, USA
3NASA/Goddard Space Flight Center, Laboratory for Solar and Space Physics, Greenbelt, MD, USA
Abstract. The winter MaCWAVE (Mountain and convective waves ascending vertically)
rocket campaign took place in January 2003 at Esrange, Sweden and the ALOMAR
observatory in Andenes, Norway. The campaign combined balloon, lidar, radar,
and rocket measurements to produce full temperature and wind profiles from
the ground to 105 km. This paper will investigate gravity wave propagation
in the mesosphere and lower thermosphere using data from the Weber sodium
lidar on 28–29 January 2003. A very large semidiurnal tide was present in
the zonal wind above 80 km that grew to a 90 m/s amplitude at 100 km. The
superposition of smaller-scale gravity waves and the tide caused small
regions of possible convective or shear instabilities to form along the
downward progressing phase fronts of the tide. The gravity waves had periods
ranging from the Nyquist period of 30 min up to 4 h, vertical
wavelengths ranging from 7 km to more than 20 km, and the frequency spectra
had the expected –5/3 slope. The dominant gravity waves had long vertical
wavelengths and experienced rapid downward phase progression. The gravity
wave variance grew exponentially with height up from 86 to 94 km, consistent
with the measured scale height, suggesting that the waves were not
dissipated strongly by the tidal gradients and resulting unstable regions in
this altitude range.
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