MG+ airglow in the low latitude ionosphere: observations and theoretical modelling

The study of the F region metal ion morphology is important because the long-lived ions are tracers of the dynamical processes operating in this region. The behavior of Mg+ was inferred from the 2800 A resonance emission observed by the Visible airglow Experiment on the Atmosphere Explorer E satellite. Observations were obtained during northern winter, solar maximum conditions in 1978 to 1979 and 1979 to 1980. A two-dimensional inversion technique was developed which produces altitude profiles of the number density of the emitting species, referenced to geographic position, from column brightnesses observed by spinning satellites. The Mg+ altitude profiles, restricted to the range of 300 to 475 km, revealed the presence of relatively large number densities approx. 50 to 100 cm-3, which were nearly constant in altitude. This configuration first appeared at 12 to 14/sup h/ within 100N of the dip equator for the Asian and African sectors (geographic longitudes 600E to 1500W and 300W to 600E, respectively) and in the interval 50 to 100N dip latitude in the American sector (geographic longitudes 1500W to 300W). Subsequently, the equatorial densities decreased with time in the Asian and African sectors with larger densities and the steep number density profiles being seen to the north in Asia and in both the north and south in Africa. The American, in contrast, increased in density with time at latitudes with time at latitudes within 150 of the dip equator. In all sectors, the densities at dip latitudes greater than or equal to 200 remain small and essentially constant all day. Theoretical modelling of the Mg+ number density was undertaken by solving the coupled continuity and momentum equation for one major and one minor ion. A uniform layer of 100 ions cm-3 at 125 km was assumed