ATMOSPHERIC WINDS CALCULATED FROM DIURNAL CHANGES IN THE MIDLATITUDE IONOSPHERE

Diurnal variations in the electron content (N(t)) and peak density (N( m)) of the ionosphere are calculated using a full time-varying model w hich includes the effects of electric fields, interhemispheric fluxes and neutral winds. The calculation is iterated, adjusting the assumed hourly values of neutral wind until a good match is obtained with mean experimental values of N(t) and N(m). Using accurate ionospheric data for quiet conditions at 35-degrees-S and 43-degrees-S, winds are deri ved for summer, equinox and winter conditions near solar maximum and s olar minimum. Solar maximum results are also obtained at 35-degrees-N. Changes in the neutral wind are found to be the major cause of season al changes in the ionosphere, and of differences between the two hemis pheres. Calculated winds show little variation with latitude, but the winds increase by about 30% at solar minimum (in equinox and winter). The HWM90 wind model gives daytime winds which are nearly twice too la rge near solar maximum. The theoretical VSH model agrees better with o bserved daytime variations, and both models fit the observed winds rea sonably well at night. Results indicate that modelling of the quiet, m id-latitude ionosphere should be adequate for many purposes when impro ved wind models are available. Model values for the peak height of the ionosphere are also provided; these show that wind calculations using servo theory are unreliable from sunrise to noon and for several hour s after sunset.