Seasonal behaviour of Mars' northern polar vortex

Streeter, Paul; Lewis, Stephen; Holmes, James; Rajendran, Kylash and Patel, Manish (2022). Seasonal behaviour of Mars' northern polar vortex. In: BPSC2022: 3rd British Planetary Science Conference, 22-24 Jun 2022, Milton Keynes, UK.



Like Earth, Mars has polar vortices: regions of cold air above the winter pole, circumscribed by powerful jets. Understanding the nature of Mars' polar vortices, and how they behave under different atmospheric dust conditions, is important for understanding the current and ancient martian climate, including the chemical and aerosol cycles. In this work we present a climatology of eight martian years of the northern polar vortex, constructed via data assimilation [1] of orbital temperature and dust measurements [2] into a Mars global climate model [3]. We show that the large-scale seasonal behaviour and characteristics of the northern vortex are highly interannually repeatable, though with the important exception of dust storm activity. Previous work [e.g. 4] has focused on individual regional or global dust events, and specifically solstice-time for the latter; by investigating a full eight-year period containing two global and numerous regional dust storms, we are able to investigate the potentially crucial effects of dust storm seasonal timing on vortex behaviour, as suggested by previous work [5]. We find that the timing of atmospheric dust events has a critical role in controlling storm dynamical effects on the northern polar vortex. Storms which occur later in Mars' perihelion (dusty) season, such as solstitial global dust storms and C-type regional dust storms [6], have a greater impact in disrupting both the morphology (including latitudinal extent) and intensity of the vortex than those early in the season, such as equinoctial global dust storms and A-type regional dust storms.

[1] S. R. Lewis, M. Collins, and P. L. Read, “Data assimilation with a martian atmospheric GCM: an example using thermal data,” Advances in Space Research , vol. 19, pp. 1267–1270, May 1997.

[2] D. J. McCleese, J. T. Schofield, F. W. Taylor, S. B. Calcutt, M. C. Foote, D. M. Kass, C. B. Leovy, D. A. Paige, P. L. Read, and R. W. Zurek, “Mars Climate Sounder: An investigation of thermal and water vapor structure, dust and condensate distributions in the atmosphere, and energy balance of the polar regions,” JGR: Planets , vol. 112, p. E05S06, May 2007.

[3] F. Forget, F. Hourdin, R. Fournier, C. Hourdin, O. Talagrand, M. Collins, S. R. Lewis, P. L. Read, and J.-P. Huot, "Improved general circulation models of the Martian atmosphere from the surface to above 80 km," JGR: Planets, vol. 104, pp. 24155-24175, Oct. 1999.

[4] S. D. Guzewich, A. D. Toigo, and D. W. Waugh, "The effect of dust on the martian polar vortices," Icarus, vol. 278, pp. 100-118, Nov. 2016.

[5] P. M. Streeter, S. R. Lewis, M. R. Patel, J. A. Holmes, A. A. Fedorova, D. M. Jass, and A. Kleinböhl, "Asymmetric Impacts on Mars' Polar Vortices From an Equinoctial Global Dust Storm," JGR: Planets, vol. 126, no. 5, p. e2020JE006774, 2021.

[6] D. M. Kass, A. Kleinböhl, D. J. McCleese, J. T. Schofield, and M. D. Smith, "Interannual similarity in the Martian atmosphere during the dust storm season," GRL, vol. 43, p. 2016GL068978, June 2016.

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