Diurnal and seasonal variations of orographic clouds in the Tharsis region with EMM/EXI observations and the Mars Planetary Climate Model

Abstract

The diurnal and seasonal variations of orographic water ice clouds in the Tharsis region have been investigated with EXI observations for MY 36 and 37. In order to provide context, meteorological fields from the Mars PCM (Mars Planetary Climate Model led by Laboratoire de Météorologie Dynamique Paris, France) have been incorporated. These fields include water ice column, atmospheric temperature, meteorological winds, water vapor, and dust mixing ratio. The diurnal cycle has been studied for sunlit hours (6 am–6 pm) by sampling data into 5 local time bins. Both the EXI observations and the Mars PCM underscore the significant role plays by diurnal thermal tides in controlling the thickness and existence of water ice clouds in the Tharsis region. During Spring and Summer, water ice clouds form in the morning and late-afternoon hours and exhibit greater thickness compared to those that form during the afternoon, primarily due to the influence of thermal tides. During Fall and Winter, water ice clouds are typically observed in the Arsia Mons region, occasionally extending to the Pavonis Mons region. During the Fall and Winter seasons, the clouds that form are mostly thin and have a tendency to develop in the afternoon hours, while the morning hours typically remain cloud-free or exhibit extremely thin clouds. This phenomenon can be attributed to a combination of factors, including the existence of cold temperature zones at higher altitudes formed by the influence of strong trade winds and the impact of diurnal thermal tides. According to the Mars PCM, water ice clouds typically form at altitudes below 25 km during Spring and Summer, whereas during Fall and Winter, cloud formation occurs at altitudes above 25 km.