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8 1. INTRODUCTION
of the limb-scanning instruments can measure to as high as 80° latitude, providing near-
global coverage [Reber et al., 19931. The UARS has two instruments for thermospheric wind
measurements. They are a high resolution Doppler imager (HRDI) and a wind imaging inter-
ferometer (WINDII). The HRDI is a triple-etalon Fabry-Perot interferometer/-photometer
which measures the horizontal wind and atmospheric temperature from the Doppler shift
of the 02 atmospheric band (b' X3 E;) absorption and emission features, respectively.
Morton et al. [1993] and Burrage et al. [1994] presented preliminary results of a study
of mesospheric and lower thermospheric diurnal tidal winds obtained with the HRDI on
the UARS. The obtained maximum amplitude of meridional wind is approximately 75 m/s.
The observed vertical wavelength is about 20 km, with amplitudes increasing linearly with
height. The WINDII takes advantage of airglow emission lines photochemically produced
from species in the upper mesosphere (OH), the lower thermosphere (02, O(1S)) and the
middle thermosphere (0(1S), O(1D) and 0+(2P)) for the measurement of winds and tem-
peratures in the altitude range 80 to 300 km. The instrument consists essentially of a charge
coupled device (CCD) camera viewing the Earth's limb through a field-widened Michelson
interferometer. Shepherd et a/. [1995] presented a review of the Doppler imaging concept,
its implementation in the WINDII and the current status of validation and data process-
ing. McLandress et al. [1996] analyzed thermospheric winds measured by the WINDII for
migrating solar tides, and reported some interesting features of thermospheric tides.
1.4 Ground-based observations of the high-latitude
thermospheric neutral wind
1.4.1 Upper thermosphere
Fabry-Perot interferometers have been used for many years to measure winds and tem-
peratures in the upper thermosphere from line-of-sight Doppler shifts of the 01630.0 nm
emission line, for example Armstrong [1969], Hays and Roble [1971], Hernandez and Roble
[1976], Sipler and Biondi [1979], Jacka et al. [1979], Hays et al. [1979], Burnside et al.
[1981] and others. A classical Fabry-Perot interferometer has a photomultiplier at the center
of a pinhole in the image plane of interference fringes by a Fabry-Perot etalon. Scanning
of the etalon by changing the pressure within the etalon cavity or by a physical change of
the etalon's plate separation has widely been used as a mean of producing an emission line
spectrum.