UV Dayglow Variability on Mars: SimulationWith a Global Climate Model and ComparisonWith SPICAM/MEx Data

摘要

A model able to simulate the CO Cameron bands and the CO_2~+ UV doublet, two of the most prominent UV emissions in the Martian dayside, has been incorporated into a Mars global climate model. The model self-consistently quantifies the effects of atmospheric variability on the simulated dayglow for the first time. Comparison of the modeled peak intensities with Mars Express (MEx) SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) observations confirms previous suggestions that electron impact cross sections on CO_2 and CO need to be reduced. The peak altitudes are well predicted by the model, except for the period of MY28 characterized by the presence of a global dust storm. Global maps of the simulated emission systems have been produced, showing a seasonal variability of the peak intensities dominated by the eccentricity of the Martian orbit. A significant contribution of the CO electron impact excitation to the Cameron bands is found, with variability linked to that of the CO abundance. This is in disagreement with previous theoretical models, due to the larger CO abundance predicted by our model. In addition, the contribution of this process increases with altitude, indicating that care should be taken when trying to derive temperatures from the scale height of this emission. The analysis of the geographical variability of the predicted intensities reflects the predicted density variability. In particular, a longitudinal variability dominated by a wave-3 pattern is obtained both in the predicted density and in the predicted peak altitudes.