The asymmetric effects of an equinoctial Global Dust Storm on Mars’ polar vortices

Streeter, Paul; Lewis, Stephen; Patel, Manish; Holmes, James; Fedorova, Anna; Kass, David and Kleinböhl, Armin (2021). The asymmetric effects of an equinoctial Global Dust Storm on Mars’ polar vortices. In: National Astronomy Meeting 2021, 19-23 Jul 2021, Virtual.



Like Earth, Mars has dynamical atmospheric features known as polar vortices. These are regions of cold, isolated polar air surrounded by powerful westerly jets which can serve as barriers to transport of atmospheric dust, water, and chemical species. Unlike Earth, Mars also experiences planet-encircling Global Dust Storms which can last for months and have significant meteorological effects. The most recent such event in 2018 (beginning at northern autumn equinox) was observed by multiple spacecraft, enabling the opportunity to study its effects on the polar vortices in detail. We do this by assimilating spacecraft data from the Mars Reconnaissance Orbiter and the ExoMars Trace Gas Orbiter into a 4D numerical model of the martian atmosphere. We find that the storm had asymmetrical impacts in each hemisphere: the northern polar vortex remained relatively robust, while the southern polar vortex was significantly disrupted. This asymmetry was due to both the storm’s latitudinal extent, which was greater in the south than in the north, and its timing, occurring as the southern vortex was already decaying after equinox. Both polar vortices and especially the northern showed reductions in their ellipticity, and this correlated with a reduction in high-latitude stationary wave activity in both hemispheres. We show that the characteristic elliptical shape of Mars’ polar vortices is the pattern of the stationary waves; this was suppressed during the storm by the shifting of the polar jet away from regions of high mechanical forcing in the north, and by the reduced polar jet due to the decreased meridional temperature gradient in the south. These asymmetric effects suggest enhanced transport into the southern, but not northern, polar region during Global Dust Storms around northern autumn equinox, as well as more longitudinally symmetric transport around both poles.

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