Measurements of Upper-Atmosphere Rotational Speed from Changes in Satellite Orbits
ROYAL AIRCRAFT ESTABLISHMENT FARNBOROUGH (UNITED KINGDOM)
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The rotation of the upper atmosphere subjects a satellite to an aerodynamic force normal to the orbit, which has the effect of slightly reducing the inclination of the orbit to the equator. The average rotational speed of the upper atmosphere at heights a little above that of perigee can be evaluated from the observed changes in orbital inclination. Since the change in inclination is small less than 0.1 degree, the values generally have to be averaged over several months, and they can also be regarded as applying over latitudes up to about half the inclination, the effects being strongest at the equator. Recent results reviewed in the report confirm a previous finding that the upper atmosphere at heights of 200 to 350 km rotates on average faster than the Earth, and that the average rate of rotation increases with height from about 1.1 revday at 200 km to nearly 1.4 revday at 350 km. However, it appears that the rotation rate decreases above 350 km, to about 1.0 revday at 420 km and 0.7 revday at 500 km.
- Atmospheric Physics
- Spacecraft Trajectories and Reentry