UV Dayglow Variability on Mars: Simulation With a Global Climate Model and Comparison With SPICAM/MEx Data

摘要

abstract_textpA model able to simulate the CO Cameron bands and the CO2+ 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 CO2 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./ppPlain Language Summary The analysis of the radiation emitted by atmospheric species has long been used to derive information from planetary atmospheres. In this work we focus on two of the most intense emissions produced on the dayside of Mars in the UV range. For the first time we have simulated these emissions using a global model covering the whole planet, in contrast with all previous models that only considered a single vertical profile. We have validated our model with observations from the SPICAM instrument on board the European Space Agency spacecraft Mars Express. We have studied the variability of the emissions as predicted by our global model. We have found that the variability of the atmospheric density induces a similar variability in the emissions. While previous results indicated that both emission systems were produced basically from CO2 only, we have found a significant contribution from CO to one of them. This complicates the derivation of the atmospheric temperature from the vertical variation of that emission./p/abstract_text