Seasonal and Inter-Annual Variability in the Polar Vortex and Snowfall on Mars

Abstract

The polar vortices of Mars are characterized by strong zonal winds that isolate cold air above the pole, allowing CO₂ to condense out of the atmosphere through snowfall and direct deposition. Due to their key role in seasonal variability of the atmosphere, it is important to understand the different factors that affect the strength, shape, and stability of the polar vortices and processes such as snowfall that occur within. We used atmospheric retrievals of temperature and CO₂ ice cloud opacity from the Mars Climate Sounder (MCS) on board NASA's Mars Reconnaissance Orbiter (MRO) to characterize and analyze patterns in the polar vortices and CO₂ ice clouds for Mars years (MY) 29–36. We couple the MCS data with a one-dimensional snowfall model to determine CO₂ snow precipitation rates and analyze patterns in the amounts and distribution of snowfall. We characterize the elliptical nature of both vortices and find that there is significant shrinking and warming of the polar vortex during regional dust storms in the summer hemisphere, which occur more frequently during northern winter. We also find that snowfall in the north pole exceeds that in the south and accounts for ∼1% of surface CO₂ deposition, with a notable pause in snowfall during the solstice. We also find measurable variability in snowfall driven by both regional and global dust storms and persistent yearly patterns in the spatial distribution of snow clouds.