Climate and Chemistry on Mars

The climate of the Martian atmosphere was subject of studies since the late 1960s. After Mariner 4 provided the first pictures of the Mars surface in 1964, lander missions were prepared and knowledge of the Mars atmosphere, especially its winds was desired. Leovy & Mintz (1969) provided the first general circulation model (GCM) of the Martian atmosphere. Subsequently five more and more complex GCMs from research groups in the US, France, UK, Canada and Japan followed. In 2005 we published a description of the MPS GCM and its climatology (Hartogh et al., 2005). Especially its prediction of the upper Martian atmosphere temperature structure, not constrained by observations yet was subject of debate, because the MPS model diverged substantially from the prediction of all other models mentioned above and it was a big success when the first observation of Mars Climate Sounder published in 2008 (McCleese et al, 2008) confirmed our predictions rather precisely. First attempts to add photochemistry into the model followed (Sonnemann et al, 2010) and the physics in the model, especially the effect of waves was permanently improved (e.g. Medvedev et al. 2011). A sophisticated water cycle was implemented and the recently observed unexpected high amounts of water vapor in the upper Martian atmosphere were explained by using our model (Shaposhnikov et al, 2019).

Recently new, very sensitive observation of the ExoMars Trace Gas Orbiter (TGO) and its instruments NOMAD (Nadir and Occultation for MArs Discovery) an ACS  (Atmospheric Chemistry Suite) became available and initiated a number of interesting scientific questions. Some of them, formulated and described below are part of the proposed PhD using the MPS-GCM project:
 

1. The D/H ration in the present Martian atmospheric water is at least 5 times VSMOW. This fact is believed to be an indication of a large loss of Martian water to space, because thermal (Jeans) escape of hydrogen is more likely than deuterium escape. TGO observations showed an increased transport of water vapour into the upper atmosphere (Fedorova et al, 2020) and escape of hydrogen (Chaffin et al, 2021) during dust storms and provided vertically resolved HDO observations (Villanueva et al, 2021). How are H2O and HDO transported from the surface/troposphere to the thermosphere, considering advection, cloud microphysics - related and photochemical fractionation effects? Does the model quantitatively confirm the observed increase in H escape during dust storms? How does the deuterium escape correlate with the hydrogen escape?
2. The ACS MIR instrument observed for the first time HCl in the Martian atmosphere (Olsen, 2021). HCl is believed to be of volcanic origin, however the observations on Mars show a correlation with the humidity and the amount of dust in the atmosphere. HCl lines never appears in the MIR spectra without water lines. The hydration of NaCl (in the dust) and subsequent oxidation by HO2 is proposed as the main production process of HCl.  Generally, HCl disappears rapidly once the dust disappears.  There is no easy explanation, because the photochemical lifetime of HCl is large and it is speculated that the HCl falls down to the lowest height levels above the surface, where the MIR sensitivity is not sufficient. Alternatively, HCl may be integrated into or on the surfaces of water ice particles during its decent. Thus far no quantitatively sound pathway was identified. The idea is to use our GCM including the microphysics part in order to quantitatively evaluate the proposed pathways on HCl sources and sinks.
3. Relatively large amounts of molecular oxygen in the Martian atmosphere were observed from ground under favourable conditions in the early 1970s for the first time. It took nearly 40 years until high signal-to-noise observations of Herschel confirmed the observations (Hartogh at al. 2010), and provided for the first time the possibility to constrain the vertical distribution of O2. While most observations showed the expected constant vertical profile (large photochemical lifetime of O2 like on Earth), in one case a decay with altitude was observed. Curiosity observations of O2 in the Gale crater showed a larger than expected annual and seasonal variation (Trainer et al, 2019). There is no obvious explanation for these observations, suggesting an unknown atmospheric or surface process at work. New data of TGO about the vertical profile of O2 will come soon and may provide additional insights into this problem. The idea is to tackle this problem by the development of hypotheses and their quantitative evaluation with the model.

 
C. Leovy and Y. Mintz, Numerical Simulation of the Atmospheric Circulation and Climate of Mars, JAS, vol. 26, I6, 1969.
 
P. Hartogh, A. S. Medvedev, T. Kuroda, R. Saito, G. Villanueva, A. G. Feofilov, A. A. Kutepov, and U. Berger, Description and climatology of a new general circulation model of the Martian atmosphere, J. Geophys. Res., 110, E11008, doi:10.1029/2005JE002498, 2005.
 
D.J. McCleese et al: Intense polar temperature inversion in the middle atmosphere on Mars, Nature Geoscience, Volume 1, Issue 11, pp. 745-749 (2008).
 
G. R. Sonnemann, P. Hartogh, M. Grygalashvyly, and A. Medvedev, A New Coupled 3D-Model of the Dynamics and Chemistry of the Martian Atmosphere, in: Advances in Geosciences (edited by A. Bhardwaj, S. A. Haider, P. Hartogh, W.-H. Ip, T. Ito, Y. Kasaba, G. M. Muños Cara, and C. Y. R. Wu), vol. 19, pp. 177–194, World Scientific Publishing Co., Singapore, 2010.
 
S. Medvedev, E. Yi?it, P. Hartogh, and E. Becker, Influence of gravity waves on the Martian atmosphere: General circulation modeling, J. Geophys. Res., 116, E10004, doi:10.1029/2011JE003848, 2011.
 
D. S. Shaposhnikov, A.S. Medvedev, A.V. Rodin and P. Hartogh, Seasonal Water "Pump" in the Atmosphere of Mars: Vertical Transport to the Thermosphere, GRL 46, I8, doi:10.1029/2019GL082839, 2019.
 
Anna Fedorova et al: Stormy water on Mars: The distribution and saturation of atmospheric water during the dusty season, Science 367, 6475, doi:10.1126/science.aay9522, 2020.
 
M.S. Chaffin et al: Martian water loss to space enhanced by regional dust storms, Nature Astronomy, doi:10.1038/s41550-021-01425-w, 2021.
 
G.L. Villanueva et al: Water heavily fractionated as it ascends on Mars as revealed by ExoMars/NOMAD, Science Advances, 7, doi:10.1126/sciadv.abc8843, 2021.
 
K.S. Olsen et al, Seasonal reappearance of HCl in the atmosphere of Mars during the Mars year 35 dusty season, A&A, 647, A161, doi:10.1051/0004-6361/202140329, 2021.
 
P. Hartogh et al: Herschel/HIFI observations of Mars: First detection of O2 at submillimetre wavelengths and upper limits on HCl and H2O2, Astron. & Astrophys., 521, L49, doi:10.1051/0004-6361/201015160, 2010.
 
M.G. Trainer, Seasonal Variations in Atmospheric Composition as Measured in Gale Crater, Mars, JGR: Planets, 124, 11,  doi:10.1029/2019JE006175, 2019