The morphology of equatorial Mg⁺ ion distribution deduced from 2800‐Å airglow observations

The Visible Airglow Experiment on the Atmosphere Explorer E satellite has observed the resonantly scattered emission from Mg II at 2800 Å in the equatorial ionosphere. Altitude profiles of the Mg + ion distribution have been obtained from the inversion of the surface brightness measurements made on spinning orbits. These data show a daytime metallic ion layer between 150 and 200 km developing in the early morning and reaching about 100 ions/cm³ in the afternoon. Mg + ions are also seen in the F 2 region mostly in the late afternoon hours within a few degrees of the dip equator. The study of the vertical column density measured in the despun mode indicates that the amount of Mg + in the F region is most variable in the afternoon hours at low dip latitudes. These results can be explained in part by the diurnal variation of the E × B drift velocity which lifts the metallic ions up into the F region. The observations suggest that the vertical polarization electric field is not the primary transport mechanism extracting the Mg + ions from the low‐altitude source layer.