Analysis and modeling of the GLO-1 observations of meteoric metals in the thermosphere

The GLO-1 experiment measured the radiance of ambient atmospheric species a nd of meteoric metals, including Na, Mg, Mg+ and Ca+, along lines of sight with tangent altitudes between 120-350 km. The results confirm earlier obse rvations of a strong dawn/dusk asymmetry in thermospheric ion density and t he concentration of ion density near the geomagnetic equator. The data also show a substantial amount of neutral Na in the thermosphere, with a dawn/d usk asymmetry similar to the ions. We observe the presence of Ca+ and Mg+ i n the relative abundance comparable to the abundance ratio in meteoric mate rial and in the sun. We are also able to simultaneously observe Mg and Mgin a few cases, over a range of altitudes. We have developed a model in an attempt to better understand these features. The one-dimensional model real istically and comprehensively incorporates the deposition of cosmic dust, t ransport by the equatorial electric held and diffusion, and ion and neutral chemistry specific to the three metal species studied. The model is driven by a single source function for dust influx, so that it can be used to pre dict the relative amounts of one metal species to another. These features o f the model allow for diurnal variations and variations in latitude, reprod ucing the observations reasonably well on average. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.