Characterization of warm layers on Mars with the Imaging Ultraviolet Spectrograph on board the Mars Atmosphere and Volatile Evolution spacecraft
Résumé
Four-year stellar occultation observations performed by the Imaging Ultraviolet Spectrograph (IUVS) on board the Mars Atmosphere and Volatile Evolution spacecraft has accumulated hundreds of vertical profiles of temperature and aerosol opacity, as well as the density profiles of molecular species, such as carbon dioxide, oxygen, and ozone in the mesosphere of Mars. These observations span two Mars years and are advantageous for investigating the seasonal and annual variations of Martian mesosphere, which will significantly advance our understanding of the coupling of lower and upper atmosphere. A recent ongoing study with IUVS stellar occultation data of Ls = 0° - 180° by Nakagawa et al. (this conference; Abstract ID# 504703) revealed a warm layer at an altitude of 70 - 90 km in the summer nightside mesosphere of Mars, which worked as an intermediate reservoir of water vapor and thus impacted the water loss to space. In this study, we extend the work of Nakagawa et al. by making a statistical study of warm layers with the IUVS stellar occultation measurements within two Mars years. Preliminary analysis showed that all warm layers occurred at a pressure level of 0.1 - 0.01 Pa and in the nighttime of Mars. The distribution of warm layers exhibited strong spatial and temporal variations. We also investigate the relationship between the variations of dust opacity and the behavior of warm layers.