Enhanced Super-rotation before and during the MY34 Martian Global Dust Storm

The presence of an equatorial westerly jet in a planetary atmosphere is often referred to as super-rotation. On Mars, super-rotation affects – and is affected by – the distribution of dust in the atmosphere. We used data assimilation to study the interaction between dust and the equatorial jet during the MY34 Mars global dust storm (GDS). The data assimilation scheme integrated temperature and dust retrievals from the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter and the Atmospheric Chemistry Suite aboard the ExoMars Trace Gas Orbiter into a numerical model of the Martian atmosphere. This created a better representation of the atmospheric state than could be achieved from the observations or the model alone.

We found that super-rotation increased by a factor of two at the peak of the GDS, as compared to the same period in the previous year which did not feature a GDS. A strong westerly jet formed in the tropical lower atmosphere, and easterlies were strengthened above 60 km, as a result of momentum transport by dust-driven thermal tides. We found that the atmosphere was in a state of enhanced super-rotation even before the onset of the GDS, as a result of equatorward advection of dust from the southern mid-latitudes into the tropics. The redistribution of dust across the hemispheres resulted in a more uniform dust distribution across the tropics, leading to a symmetric Hadley cell with a tropical upwelling branch that was closely aligned to the vertical. We argue that the symmetrical circulation and enhanced super-rotation were important environmental factors that encouraged the rapid development of the MY34 GDS.