Detection of Mesospheric CO 2 Ice Clouds on Mars in Southern Summer

This paper reports the first detections of two high‐altitude nighttime CO 2 clouds on Mars during southern summer ( L s =264° and L s =330°) with stellar occultation measurements by the Imaging Ultraviolet Spectrograph on board the Mars Atmosphere and Volatile Evolution spacecraft. Interpretation of the transmission spectra with Mie theory indicates particle radii of ∼90–110 nm assuming a monodisperse distribution. The altitude profile of extinction indicates that the cloud layers are confined horizontally to sizes less than ∼500–700 km. Examination of the CO 2 density and temperature profiles reveals strong wave‐like perturbations. Supersaturated temperatures occur at the maximum negative extent of these wave‐like perturbations, which are organized in longitude with a dominant m =3 zonal harmonic. This suggests that tides are important in the formation of CO 2 clouds.