The Dependence of the Circulation of the Thermosphere on Solar Activity.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OHIO
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Incoherent scatter radar measurements of the ionospheric electron density, electron and ion temperature, and vertical ion drift made at the Millstone Hill Observatory were used to derive the neutral temperature and a measure of the neutral winds in the mid-thermosphere. Over the six year period 1970, near solar maximum, through 1975, at solar minimum, 83 days of diurnally averaged winds were examined to determine if there was a change in the seasonal variation in the circulation as solar activity decreased. It was found that the magnitude of the seasonal variation in both the zonal and meridional winds remains about the same, although the winter averaged winds become more poleward near solar minimum consistent with the model of Roble et al 1977. For several geomagnetically disturbed days examined, it was found that the diurnal wind pattern was significantly different from quiet days. The nighttime meridional winds were markedly stronger equatorward and the zonal winds tended to be more westward. In the analysis procedures, it was demonstrated that frictional heating by the neutrals is an important factor in deriving the neutral temperature from the ion heat balance equation. It was also shown that electric field effects are important in the derivation of winds during disturbed periods.
- Atmospheric Physics