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Abstract
Incoherent scatter measurements of the ionospheric F region electron density, electron and ion temperature, and vertical ion drift made at Millstone Hill have been used to derive estimates of the exospheric neutral temperature T∞ and the horizontal component of the neutral wind along the magnetic meridian VHn. These data then were employed in a semiempirical model for the local thermosphere (Emery, 1978a) to calculate the diurnal variation of the zonal and meridional winds for the days of the measurements. A total of 64 geomagnetically quiet days from the years 1970, near solar maximum, through 1975 were analyzed. The mean meridional and zonal winds were found to exhibit a marked seasonal variation of about ±50 and ±30 m/s, respectively. The amplitude of this oscillation did not appear to decrease with decreasing sunspot activity; however, the annual mean meridional wind was found to decrease from 25 m/s equatorward to about 0 m/s over the 6‐year period. It is believed that this is indicative of a decrease in the auroral forcing relative to the solar forcing at solar minimum. The meridional winds near equinox shifted from being generally equatorward at solar maximum to being poleward at solar minimum, also suggesting decreased auroral forcing. The diurnally averaged zonal winds maintained a fairly consistent pattern of eastward winds in winter and westward winds in summer over the 6‐year interval.
Published Version
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