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The circulatory impact of dust from dust profileassimilationConference or Workshop ItemHow to cite:

Streeter, P. M.; Lewis, S. R.; Patel, M. R. and Holmes, J. A. (2018). The circulatory impact of dust fromdust profile assimilation. In: Mars Science Workshop "From Mars Express to ExoMars", 27-28 Feb 2018, ESAC,Madrid, Spain.

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The circulatory impact of the vertical dust structurePaul Streeter1, Stephen Lewis1, Manish Patel1,2, & James Holmes1

1School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK, 2Space Science and Technology Department, STFC, RAL, UK (paul.streeter@open.ac.uk)

Dust Profile Assimilation• Mineral dust is the key radiative forcer in the martian atmosphere.• Data assimilation: LMD-UK MGCM + observations = best estimate of state (e.g. [1]).• Vertical dust structure shown by MCS to be more complex than previously assumed [2].• MCS dust profiles and columns are assimilated to examine impact on the circulation andtransport (“3D”), and compared to a MCS column-only assimilation (“2D”) for MY 31.

Schematic showing assimilated model (right) as combination of TES dust opacity observations (top left) and a free-running MGCM (bottom left).

Zonal Temperatures and Winds Transport

• Vertical dust structure has significant impact on temperature structure, globalcirculation, and transport.• Circulatory impact of increased elevated dust presence appears greatest during lower-insolation times of year: mitigates effect of hemispheric topographic asymmetry and dramatically strengthen the NS Hadley cell. Stronger Hadley cells overall.• Reduced near-surface eddy activity; possible explanation for southern dust exclusion.• TGO will offer a new dataset of dust profiles across a range of martian local times.

Summary

Major difference between assimilation cases is significantly warmer lower-middle atmosphere for the 3D case, due to greater dust representation above 10 km, and enhanced polar warming. Northern polar warming is also shifted higher, potentially heating the lower thermosphere.

In general, 3D case shows strengthened circulation, including as a strengthened southern polar jet; however, northern polar jet mostly unaffected, although strengthened at very high altitudes.

Asymmetry implies vertical dust distribution (ie. more dust higher up) has most significant effect around “clear” season, when insolation is lower and more high-altitude dust layers are present.

Seasonal asymmetry also related to topography: elevated dust layers act to mitigate topographic asymmetry [3,4] by providing elevated heating source in northern hemisphere.

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Acknowledgements

3D assimilation shows lower dust mass in southern polar vortex despite higher overall.

Mean meridional circulation (MMC) structure sees greatest difference around southern winter, with dramatically intensified Hadley cell. Suggests extra high-altitude dust mitigates topographic effects, as high dust loading can [6]. This has implications for long-term inter-hemisphere transport.

3D case sees some reduced surface eddy activity (Ferrel cells) due to greater lower-atmosphere static stability, which could impact eddy dust transport into polar regions. However, also see increased eddy activity at higher altitudes, due to increased thermal contrast at dust layer top.

PMS 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 Francois Forget and colleagues (LMD/CNRS Paris).

Better fit with observed dust exclusion over southern polar vortex [5], suggesting dynamical explanation.

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3D 3D-2D

3D 2D

Above: zonal-mean temperatures and zonal winds for assimilated output from 3D assimilation (left) and the difference between 3D and 2D assimilation (right), averaged over ~15 solar longitude degrees for three periods in MY 31 using MCS data.Top right: average dust mass mixing ratio over southern polar vortex for 3D and 2D assimilations.Bottom right: mean meridional circulation for same periods as above zonal mean plots.

Figures:

References[1] Lewis, S. R., Read, P. L., Conrath, B. J., Pearl, J. C. & Smith, M. D. Assimilation of thermal emission spectrometer atmospheric data during the Mars Global Surveyor aerobraking period. Icarus 192, 327–347 (2007). [2] McCleese, D. J. et al. Structure and dynamics of the Martian lower and middle atmosphere as observed by the Mars Climate Sounder: Seasonal variations in zonal mean temperature, dust, and water ice aerosols. J. Geophys. Res. Planets 115, E12016 (2010). [3] Richardson, M. I. & Wilson, R. J. A topographically forced asymmetry in the martian circulation and climate. Nature 416, 298–301 (2002). [4] Takahashi, Y. O. et al. Topographically induced north-south asymmetry of the meridional circulation in the Martian atmosphere. J. Geophys. Res. Planets 108, 5018 (2003). [5] McCleese, D. J. et al. Comparisons of Observations and Simulations of the Mars Polar Atmosphere. in 1104 (2017). [6] Zalucha, A. M., Plumb, R. A. & Wilson, R. J. An Analysis of the Effect of Topography on the Martian Hadley Cells. J. Atmospheric Sci. 67, 673–693 (2010).