Climatology of martian super-rotation in the OpenMARS reanalysis

Rajendran, Kylash; Lewis, Stephen; Holmes, James; Streeter, Paul and Patel, Manish (2022). Climatology of martian super-rotation in the OpenMARS reanalysis. In: 44th COSPAR Scientific Assembly, 16-24 Jul 2022, Athens, Greece.



A planetary atmosphere is said to be super-rotating if the total axial angular momentum of the atmosphere is greater than the angular momentum of its solid-body component. Super-rotation often takes the form of a westerly jet at the equator, and this modified tropical circulation can have significant impacts on the distribution of aerosols and chemical species in the tropics.

In this work, we present a multi-year study of super-rotation in the martian atmosphere using the OpenMARS reanalysis dataset, in order to examine the relationship between dust and tropical winds on Mars. In the reanalysis scheme, observations of temperature and dust retrieved from the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter were assimilated together with output from the Open University Mars Global Circulation Model.

We found a clear seasonal pattern in super-rotation, with peaks occurring at equinoxes and troughs at the solstices. This seasonal cycle was found to be directly related to variations in the strength of the extratropical jets. Inter-annual variability was dominated by variations in the tropical circulation, with the largest amount of variability found during the dusty season. Dust loading in the atmosphere was found to have the most significant impact on the tropical circulation close to equinox, and had surprisingly little impact at solstice. This effect was clearly seen by comparing the impacts of equinoctial and solstitial global dust storms (GDS) on super-rotation. Whereas the equinoctial GDS caused atmospheric super-rotation to increase by a factor of two, during the solstitial GDS there was barely any change in super-rotation. Our results suggest that the background atmospheric circulation has an important role in controlling the strength of atmospheric super-rotation, and therefore constrains the potential evolution mechanisms of global dust storms.

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