A MODEL FOR METEORIC MAGNESIUM IN THE IONOSPHERE

We present a model of neutral and ionized magnesium in the equatorial ionosphere at altitudes of 50-350 km. The model was developed in an at tempt to understand recent spectroscopic measurements made from the sp ace shuttle. The model incorporates ablation of cosmic dust particles, ion and neutral chemistry, diffusion, and vertical drift due to the e quatorial electric field. We find that in the absence of electric fiel d drift, there is little or no variation in Mg and Mg+ density profile s above 120 km. With the electric field included, the high-altitude be havior of the Mg+ ion changes dramatically. At dawn, almost all the io n density is confined to the 90- to 125-km altitude range, while at du sk there is significant ion density as high as 350 km. A radiance mode l is developed to allow for direct comparison with measurements. The m odel incorporates shielding of incident solar UV by ozone and variable local time of observation and tangential height of instrument line of sight. Comparisons between model and measurement are encouraging.