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Very large vertical and longitudinal gradients in the ion concentrations are observed below the F peak near the magnetic equator with the retarding potential analyzer on Ogo 6. Ion concentration ‘bite outs’ of up to a factor of 10³ are observed above 400 km. They appear to be associated with the bottomside of the nighttime F layer. The ion composition in the minimums may contain large fractions of ions heavier than O+ (e.g., NO+ and Fe+). It is suggested that convective electric fields associated with spread F steepen the bottomside of the F layer and also introduce longitudinal irregularities in the vertical Ni profiles.
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Hanson et al. (1973) studied this question.
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