Analysing martian polar dust transport using data assimilation

Streeter, Paul; Lewis, Stephen; Patel, Manish and Holmes, James (2017). Analysing martian polar dust transport using data assimilation. In: 1st British Planetary Science Congress, 3-5 Dec 2017, Glasgow.

Abstract

Mars’ winter atmosphere is characterised by a polar vortex of low temperatures around the winter pole, circumscribed by a strong westerly jet. These vortices have a significant effect on the atmospheric circulation and on dust and volatile transport: modelling work has shown that increasing model dust opacity has a large effect on the northern vortex, but little effect on the southern vortex [1]. Meanwhile, new MCS retrievals with updated, 2D geometry [2] have revealed a sharp exclusion of dust aerosol from the southern polar vortex, despite the presence of transported water ice; the northern polar vortex displays less dust exclusion and a greater water ice abundance [3]. This exclusion remains to be explained, as does a more general characterisation of how dust drives and is driven by Mars’ polar atmosphere.

This study uses data assimilation to integrate MCS temperature and dust profiles into a Mars Global Circulation Model. While MCS dust profiles have been assimilated before and yielded improved fit to retrievals [4,5], this represents the first attempt to assimilate dust profiles for this purpose specifically using new and improved MCS 2D retrievals. By combining our best model and our most comprehensive observations, dust profile assimilation offers a uniquely powerful way to examine polar dust processes. Dust transport quantities and patterns are presented for the martian polar regions at various times of year, and compared to free-run models and retrievals.

[1] Guzewich, S. D., Toigo, A. D. & Waugh, D. W. The effect of dust on the martian polar vortices. Icarus 278, 100–118 (2016). [2] Kleinböhl, A., Friedson, A. J. & Schofield, J. T. Two-dimensional radiative transfer for the retrieval of limb emission measurements in the martian atmosphere. J. Quant. Spectrosc. Radiat. Transf. 187, 511–522 (2017). [3] McCleese, D. J. et al. Comparisons of Observations and Simulations of the Mars Polar Atmosphere. in 1104 (2017). [4] Ruan, T. The climate of Mars from assimilations of spacecraft data. (University of Oxford, 2015). [5] Navarro, T. Etude de la météorologie de la planète Mars par assimilation de données satellite et modélisation. (Université Pierre et Marie Curie - Paris VI, 2016).

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