Mars’ polar vortices play key roles in the planet’s general circulation and atmospheric transport. The 2018 Global Dust Storm had a strong impact on dynamics at both poles, with implications for tracer transport into and around the polar regions

Holmes, James

Lewis, Stephen

Patel, Manish

Streeter, Paul

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsMartian Polar Vortex Dynamics and the 2018 GlobalDust StormConference or Workshop ItemHow to cite:Streeter, Paul; Lewis, Stephen; Patel, Manish and Holmes, James (2020). Martian Polar Vortex Dynamicsand the 2018 Global Dust Storm. In: Seventh International Conference on Mars Polar Science and Exploration, 13-17Jan 2020, Ushuaia, Argentina.For guidance on citations see FAQs.c© 2020 The AuthorsVersion: PosterLink(s) to article on publisher’s website:https://www.hou.usra.edu/meetings/marspolar2020/pdf/6042.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukMartian polar vortex dynamics and the 2018 Global Dust StormPaul Streeter1, Stephen Lewis1, Manish Patel1,2, & James Holmes11School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK, 2Space Science and Technology Department, STFC, RAL, UK (paul.streeter@open.ac.uk)Summary AcknowledgementsPMS acknowledges support from the UK Science and Technology Facilities Council under STFC grant ST/N50421X/1 and The Open University in the form of a PhD studentship. SRL, MRP and JAH acknowledge support as part of the project UPWARDS-633127, funded by the European Union Horizon 2020 Programme. SRL, MRP and JAH also acknowledge the support of the UK Space Agency/STFC under grants ST/R001405/1 and ST/P001262/1. The authors are particularly grateful for ongoing collaborations with Dan McCleese, David Kass and the MCS team (NASA-JPL) and with Peter Read (Oxford) and François Forget and colleagues (LMD/CNRS Paris).PMS is especially grateful to the Royal Astronomical Society and the Aerosol Society for providing funds enabling his presentation of this poster at the Seventh International Conference on Mars Polar Science and Exploration.References[1] Waugh, D. W. et al (2016) J. Geophys. Res. Planets, 121, 1770-1785. [2] Guzewich, S. D. et al (2016) Icarus, 278, 100-118. [3] Mitchell, D. M. et al (2015) Q.J.R. Meteorol. Soc., 141, 550-562. [4] McCleese D. J. et al (2010) J. Geophys. Res., 115(E12016). [5] Shirley J. H. et al (2018) AGU Fall Meeting Abstracts 43. [6] Lewis S. R. et al (2007) Icarus, 192(2), 327-347. [7] Kleinböhl A. et al (2017) J. Quant. Spectrosc. Radiat. Transfer, 187, 511-522. [8] Forget F. et al (1999) JGR, 104, 24155-24175.North Pole South PoleFig. 1: Potential vorticity at the 300 K isentropic surface (PV)  and zonal wind speeds averaged between 20-30 km for MY 30 and MY 34, and the difference between them, for the north (left) and south (right) poles. Each circular line represents latitudes at 10 degree intervals, with the outermost circle being at 50 degrees. For the difference plots, dashed contour lines represent negative values.Introduction Global dust storm effectsTemporal variationVertical variationMars’ winter atmosphere is characterized by a polar vortex of low temperatures around the winter pole, circumscribed by a strong westerly jet [e.g. 1]. These vortices are a key part of the atmospheric circulation and impact heavily on dust and volatile transport. They have a complex and asymmetrical (north/south) relationship with atmospheric dust loading [1]. Regional and global dust events have been shown to cause rapid vortex displacement [2,3] in the northern vortex, while the southern vortex appears more robust. This has implications for tracer transport through the zonal jets associated with the vortices [4]; a more coherent and low-latitude zonal jet should provide a more effective barrier against tracers entering the polar regions. The 2018 Mars  Global Dust Storm (GDS) was observed through its lifecycle by the Mars Climate Sounder (MCS) instrument aboard the Mars Reconnaissance Orbiter [5]; using data assimilation [6] to integrate MCS retrievals [7] with the LMD-UK Mars Global Circulation Model (MGCM) [8] offers an opportunity to examine the effects of the GDS on the polar vortices.North Pole South PoleFig. 3: As Fig. 1, but for PV at the 400 K isentropic surface and zonal winds between 30-40 km altitude.Fig. 2: difference between zonally-averaged PV (colours) and zonal wind speeds (contours) for MY 34 and MY 30 (MY 34 – MY 30), for the 300 K isentropic surface (PV) and for wind speeds between 20-30 km.➢ Fig. 1 shows the impact of the GDS on the potential vorticity (PV) and zonal wind speeds at the 300 K isentropic surface and as averaged between 20-30 km, respectively➢ In the north, the GDS reduced PV but in an asymmetrical fashion, with maxima in decreases at around 150 and 0 degrees longitude. The pattern of PV decrease indicates a poleward shift of the polar vortex➢ Northern zonal wind speeds decreased at lower latitudes (50-60 degrees) and increased at higher latitudes (60-70 degrees), with maxima in increases tracking maxima in PV decreases. Again this indicates a poleward shift of the westerly jet core➢ In the south, the highly asymmetric and already declining polar vortex showed a dramatic reduction, accelerating its decay➢ Southern zonal wind speeds decreased at all latitudes except at the location of the former PV minimum centred at 30 degrees longitude, with residual high wind speeds at very high latitudes. This shows a remnant polar vortex remained at very high latitudes➢ Fig. 2 shows the effect of the GDS throughout its lifespan on PV and zonal wind speeds➢ At the northern pole, PV decreased at latitudes centred around 60 degrees and increased poleward of that, indicating a poleward shift of the polar vortex. The greatest effect was between LS=220-240°, as the GDS decayed. There was a corresponding increase in zonal wind speeds at around 60° N➢ At the southern pole, PV simply decreased at high latitudes as the polar vortex decay wasaccelerated by high southern dust loading and corresponding warming. Wind speeds around 60° S correspondingly decreased➢ Fig. 3 shows Fig. 1 but at higher altitudes: the 400 K isentropic surface for PV and zonal winds at 30-40 km➢ In the north, PV decrease follows the lower levelpattern but there is a morestriking PV increase within20° of the pole itself. This suggests a higher altitude polar vortex➢ In the south, the resultsfollow the lower level pattern, showing consistent decrease in PV and a narrow increase in wind speeds above the pole as the polar vortex’s annular structure collapsed➢ The 2018 GDS was an equinoctial event, beginning as the northern polar vortex was growing and the southern polar vortex was decaying➢ The GDS appeared to shift the northern polar vortex poleward; the lack of high dust loading at high northern latitudes indicates this was due to the dynamical effects of an enhanced Hadley circulation➢ The GDS drastically accelerated the seasonal decay of the southern polar vortex; this was likely due to the enhanced diabatic heating from the high southern hemisphere dust loading destroying the equator-pole temperature gradient➢ The poleward shift in the highest westerly wind speeds at both poles suggests that equinoctial GDS events could allow greater tracer transport to high latitudes

Martian Polar Vortex Dynamics and the 2018 Global Dust Storm

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Martian Polar Vortex Dynamics and the 2018 Global Dust Storm

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