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We performed retrievals of dust and water–ice optical depths at select times spanning Mars years (MYs) 33 through 36. We used data taken by the Imaging Ultraviolet Spectrograph (IUVS) instrument aboard the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, whose precessing orbit allowed IUVS to image the diurnal evolution of water–ice clouds at local times throughout this MY range where they have not been studied. We created a radiative-transfer retrieval algorithm and used it to simultaneously fit the dust and water–ice optical depth of each usable spectrum in IUVS apoapse data for the majority of the MAVEN mission. We compared our results to other datasets to ensure our retrievals produced plausible values and discuss potential reasons for discrepancies. We obtained global climate model (GCM) simulations from two state-of-the-art models and compared our results to both sets of simulations. We show that there are significant differences between our water–ice retrievals and both sets of simulations, both in the spatial cloud patterns and column-integrated optical depths. We discuss the different approaches both models used for simulating these clouds and the implications for accurately modeling these clouds in future GCM work. • We investigated the diurnal evolution of water–ice clouds across several Mars years. • Global climate models struggle to reproduce the clouds patterns we observe. • Supersaturation and rapid nucleation are necessary to accurately model these clouds. • These insights may further improve global climate model predictions. [ABSTRACT FROM AUTHOR]

We derived the ultraviolet complex refractive indices of Martian dust aerosols using data from the Mars year 34 global dust storm (GDS). We used data taken by the Imaging Ultraviolet Spectrograph (IUVS) instrument aboard the Mars Atmosphere and Volatile Evolution spacecraft and surface-based derivations of the column-integrated optical depth from the Mastcam instrument on Curiosity. We first created an explicit microphysical representation of dust to compute dust-scattering properties at wavelengths within IUVS' spectral range for four dust particle-size distributions plausibly present during this GDS. We then used radiative-transfer techniques to iteratively retrieve the single-scattering albedo from IUVS data using the Mastcam-derived column-integrated optical depth as a constraint. We converted the dust single-scattering albedo into its refractive indices and report the refractive indices at the four particle-size distributions. We performed dust optical depth retrievals at another time period using several of these refractive indices and show that our preferred refractive indices produce optical depths which are consistent with optical depths derived from Mastcam data at similar times. These ultraviolet refractive indices will be particularly beneficial for future observational and theoretical studies of Martian dust. • We derived ultraviolet refractive indices of Martian dust. • These refractive indices do not vary much with wavelength. • We performed retrievals using these indices at lower dust loading conditions. • Our results produce optical depths consistent with independent derivations. [ABSTRACT FROM AUTHOR]