SIMULATIONS OF DE 1-UV AIRGLOW IMAGES

In this paper we present simulations of the UV airglow observed in selected images obtained by the spinscan auroral imager experiment on the Dynamics Explorer 1 satellite. In particular, we present one example each of observed and modeled images for the dayglow and for the nightglow. The model dayglow emissions include the O I 130.4 nm triplet (excited by both photoelectron impact excitation of O atoms and resonant scattering of the solar O I 130.4 nm triplet), the O I 135.6 nm doublet (excited by photoelectron impact excitation of O atoms), and the N2 Lyman-Birge-Hopfield (LBH) molecular bands (excited by photoelectron impact excitation of N2 molecules). The model neglects minor contributions from H I 121.6 run and N I 149.3 nm dayglow emissions. The model nightglow emissions are comprised of the same O I 130.4 nm and 135.6 nm features, but on the nightside they are produced through recombination of O+ ions. The model neglects a contribution to the nightglow O I 130.4 nm and 135.6 nm emissions due to recombination of O+ and O- ions. The results presented here demonstrate that the dayglow emissions are well understood and can be simulated with high accuracy. This allows us to determine relative contributions of the various dayglow emission sources over the disk of the Earth. For example, while the O I 130.4 nm emission is very bright and fairly uniform at about 15-20 kR over much of the disk, the optically thin LBH emissions become much larger than the O I 130.4 nm emission at the limb, with a band-integrated maximum brightness of about 35 kR. Although the image simulation code used is fairly CPU intensive, it should prove useful in studying variations in the abundances of 0 and N2 following geomagnetic storms or in extracting the dayglow contribution from images of the sunlit auroral oval, for instance. The nightglow emissions are not as well fit by the model, indicating that the O+-O- mutual neutralization source is significant and should be included in future simulations. The observed tropical arcs are somewhat narrower than produced by the model simulation, probably due to the limited spatial resolution of the model. The model results indicate that the O I 130.4 nm and 135.6 nm recombination nightglow can reach several hundred rayleighs in the middle of the tropical arcs. Although swamped by dayglow emissions, the O I recombination glow on the dayside must typically exceed a kilorayleigh.