Physics
Scientific paper
Aug 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002jastp..64.1351r&link_type=abstract
Journal of Atmospheric and Solar-Terrestrial Physics, Volume 64, Issue 12-14, p. 1351-1360.
Physics
7
Scientific paper
In the 1960s, it was deduced from observations of satellite orbits that the thermosphere rotates about 20% faster than the Earth; i.e., there is a prevailing west-to-east wind of order 100ms-1. In the seventies, this `superrotation' was explained as a consequence of the day-to-night variation of ion-drag at low latitudes, caused by the strong nighttime polarization fields generated by the F-layer dynamo. In the eighties, satellite-borne instruments measured prevailing zonal winds of only 20-30ms-1 at low latitudes. In the 1990s, global coupled thermosphere-ionosphere models indicate similar prevailing wind speeds. Can all these be reconciled? The paper briefly reviews the observations and the theory, discussing the essentials of the ion-drag explanation of superrotation. It is now clear that the local time variation of neutral air pressure is not the simple day/night variation that was assumed in the early F-layer dynamo calculations. The present-day thermospheric models can account for a prevailing west-to-east wind of 30-40ms-1 at the magnetic equator, agreeing reasonably well with the wind measurements; the discrepancy with the satellite orbital data has been reduced but not eliminated.
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