Mars's Twilight Cloud Band: A New Cloud Feature Seen During the Mars Year 34 Global Dust Storm.

We report a new water‐ice cloud feature observed during the Mars year 34 global dust storm: twilight cloud bands that routinely formed just past the evening terminator. We use images taken by the MAVEN/IUVS instrument. These bands were often latitudinally continuous, spanning over 6,000 km and were present between 18:00 and 19:00 local time. They were present for nearly the entire time IUVS imaged the evening terminator and often reached altitudes of at least 40 to 50 km during the mature phase of the storm. We compare these observations to LMD global climate model simulations. The simulations generally contain the temporal and spatial extents of the bands seen in IUVS data throughout the storm, but there are some discrepancies. We infer that these clouds formed as a result of semidiurnal thermal tides. Plain Language Summary: Water‐ice clouds and dust are among the most common particles in the Martian atmosphere, but the effect of global dust storms on cloud formation is largely unknown. We observed cloud bands that repeatedly formed near dusk during the Mars year 34 global dust storm. We saw these bands throughout the storm at locations all across the planet. We investigate this feature by using a global climate model, which predicted the formation of these cloud bands as a result of rapidly changing temperatures. The simulations of the bands contain several features seen in our observations, but not all. Key Points: We observed a new cloud formation phenomenon just after sunset during the Mars year 34 global dust storm in MAVEN/IUVS imagesGlobal climate model simulations are able to reproduce several but not all aspects of our observationsThese twilight clouds formed due to semidiurnal thermal tides [ABSTRACT FROM AUTHOR]