This session primarily focuses on the neutral atmospheres of terrestrial bodies other than the Earth. This includes not only Venus and Mars, but also exoplanets with comparable envelopes and satellites carrying dense atmospheres such as Titan or exospheres such as Ganymede. We welcome contributions dealing with processes affecting the atmospheres of these bodies, from the surface to the exosphere. We invite abstracts concerning observations, both from Earth or from space, modeling and theoretical studies, or laboratory work. Comparative planetology abstracts will be particularly appreciated.

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Co-organized by AS4/ST3
Convener: Arnaud BethECSECS | Co-conveners: Francisco González-Galindo, Arianna Piccialli
| Attendance Tue, 05 May, 16:15–18:00 (CEST)

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Chat time: Tuesday, 5 May 2020, 16:15–18:00

Chairperson: Arnaud Beth
D2895 |
Neil Lewis, Greg Colyer, and Peter Read
Super-rotation is a phenomenon in atmospheric dynamics where the axial angular momentum of an atmosphere in some way exceeds that of the underlying planet. In this presentation, we will discuss the dependency of both globally-integrated, and local metrics of super-rotation on planetary rotation rate, revealed through analysis of idealised General Circulation Model experiments. The model used here is based on the Held-Suarez benchmark for a dry, 'Earth-like' atmosphere, and results from both axisymmetric and three-dimensional experiments will be presented. Previous work has shown that the three-dimensional configuration used here will transition to a state of equatorial super-rotation if the rotation rate is reduced sufficiently from the Earth's. This motivates the question: How does super-rotation strength depend on rotation rate?

We will use the term 'global super-rotation' to refer to an atmosphere with excess of globally-integrated axial angular momentum relative to that achieved by solid body co-rotation with the underlying planet, and 'local super-rotation' to refer to the existence of some region within the atmosphere where axial angular momentum exceeds that of the underlying planet at the equator. In an inviscid, axisymmetric atmosphere, the axial component of specific angular momentum is materially conserved. Consequently, in such a system local super-rotation is forbidden, although global super-rotation may still be achieved if a meridional circulation is able to transport fluid equilibrated with the equatorial surface poleward. If the restriction of axisymmetry is lifted, then local super-rotation may exist if non-axisymmetric disturbances that act to transport angular momentum up-gradient are present. The atmospheres of Venus, the Earth, Mars, and Titan may be considered to be globally super-rotating, however only Venus and Titan exhibit permanent local super-rotation at the equator.

The results from axisymmetric experiments reveal that at high rotation rate (e.g., greater than 1/4 of the Earth's), the degree of global super-rotation scales inversely with the square of the rotation rate. In the low rotation rate limit, the degree of global super-rotation saturates, and becomes independent of rotation rate. We will show that the high, and low rotation rate dependencies can be predicted by a single analytic scaling for global super-rotation. Our three-dimensional experiments exhibit the same scaling behaviour for global super-rotation as observed in the axisymmetric experiments. The degree of global super-rotation achieved by the three-dimensional experiments is less than that of the axisymmetric experiments at high rotation rates, and greater at lower rotation rates, but in both limits the deviation from the axisymmetric 'base circulation' is small. In the low-rotation rate limit, local super-rotation is accelerated at the equator, which is consistent with the three-dimensional experiments obtaining a higher degree of global super-rotation than their axisymmetric counterparts. Estimates for global super-rotation strength on the Earth and Mars agree closely with the results of our three-dimensional numerical experiments, but Venus and Titan achieve substantially stronger global, and local super-rotation than found here. It appears that low rotation rate alone cannot induce substantial excess global super-rotation, relative to the axisymmetric base circulation we identify.

How to cite: Lewis, N., Colyer, G., and Read, P.: The dependence of global and local metrics of super-rotation on planetary rotation rate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1032, https://doi.org/10.5194/egusphere-egu2020-1032, 2019

D2896 |
Martin Airey, Giles Harrison, Karen Aplin, and Christian Pfrang

Galactic cosmic rays are ubiquitous in solar system atmospheres. On Venus, the altitude of peak ion production due to cosmic rays (the Pfotzer-Regener maximum) occurs at ~63 km, within the optically thick region of the upper clouds. This indicates the possibility of electrical effects on droplets within Venusian clouds. Motivated by this, our VENI (Venusian Electricity, Nephology, and Ionisation) project explores effects of galactic cosmic ray (GCR) induced ionisation on cloud droplets in circumstances with relevance to Venus’ atmosphere. Charge is known to lower the critical supersaturation required for cloud droplets to form; slightly larger droplets are stable at lower saturation ratios if sufficiently charged. Condensation of gas directly onto ions is also potentially possible on Venus if the atmosphere is sufficiently supersaturated. GCRs and the secondary charged particles they produce are therefore anticipated to affect cloud droplet behaviour on Venus.

Experiments have been conducted using electrically isolated droplets, through levitation in a standing acoustic wave. The droplets are monitored with a high-magnification CCD camera to determine their evaporation rate and charge. The charge is measured both by the deflection in an electric field and by passing the droplet through a custom-built induction ring. A relationship between the evaporation rate and charge of the droplets is found to be consistent with theory, allowing droplet lifetime to be predicted for a given charge. Further experiments using sulphuric acid droplets in a carbon dioxide environment offer more direct relevance to the Venusian environment and cosmic ray enhancement due to solar energetic particles (SEPs) in space weather events will be simulated using a corona source.

How to cite: Airey, M., Harrison, G., Aplin, K., and Pfrang, C.: Galactic cosmic ray induced ionisation on Venus and its effect on cloud droplet stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3000, https://doi.org/10.5194/egusphere-egu2020-3000, 2020

D2897 |
Adhithiyan Neduncheran and Sruthi Uppalapati

Lightning in Venus is still a matter of debate due to lack of evidence in optical and simultaneous radio emissions. Several evidence of electromagnetic emissions were previously measured by various landers and orbiters studying Venus atmosphere such as the Venera 13 and 14 landers, Venus Express and the Pioneer Venus Orbiter. This theoretical work proposes the mechanism of lightning is possibly due to the super-rotation of the clouds. Excessive amount of atmospheric turbulence and the formation of plumes in the clouds of Venus should possibly lead to the formation of charges in the clouds and thereby trigger lightning. As per Lorenz 2018, it is expected that there might exist charged aerosols in the lower atmosphere. This imposes another possibility of triboelectric charging mechanism which lead to lightning in the lower and middle cloud region. Lightning induced electromagnetic emissions that takes place in the clouds might be a result of momentum transfer and charge dispersion in the clouds of Venus. Venus can be considered to be an optically active planet with phenomenon like reflection and refraction ruling to some extent which possibly imposes a difficulty in lightning detection as the photons emitted during this process are scattered away. In the end, the possible lightning mechanism and difficulties related to its detection shall be discussed

How to cite: Neduncheran, A. and Uppalapati, S.: Possibility of lightning in the Venusian clouds due to Super-rotation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16220, https://doi.org/10.5194/egusphere-egu2020-16220, 2020

D2898 |
Anna Fedorova, Franck Montmessin, Oleg Korablev, Mikhail Luginin, Alexander Trokhimovskiy, Denis Belyaev, Juan Alday, Nikolay Ignatiev, Franck Lefevre, Kevin Olsen, Ehouarn Millour, Jean-Loup Bertaux, Alexey Shakun, Alexey Grigoriev, Andrey Patrakeev, Svyatoslav Korsa, Colin Wilson, Francois Forget, and Anna Maattanen

The water vapour vertical distribution is an eloquent gauge of the relative roles of the various sources, sinks and processes that control the Martian water cycle. However, its behaviour is still poorly studied while it is instrument for our understanding of the loss of water from Mars to space, which results from the transport of water to the upper atmosphere where it is disassociated to hydrogen atoms that later escape. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution with altitude. Here we present results of the Atmospheric Chemistry Suite (ACS) instrument NIR channel for the first year of TGO observations covering the almost full year from Ls 160° of the Martian year 34 (April 2018) to Ls 130° of the Martian year 35 (January 2020). Simultaneous measurements of the water vapour mixing ratio, temperature and dust vertical distribution and formation of water ice clouds allow us to constrain the complex water behaviour and estimate the saturation state of H2O. Water profiles during the 2018-2019 southern spring and summer stormy seasons show that high altitude water is preferentially supplied close to perihelion and that large supersaturation occurs even when clouds are present. Here we attempt to complete the story by studying water vapor during the northern spring and summer to explore whether saturation impacts water transport between hemispheres in this season. The data analysis of MY35 was supported by RSF (project No. 20-42-09035).

How to cite: Fedorova, A., Montmessin, F., Korablev, O., Luginin, M., Trokhimovskiy, A., Belyaev, D., Alday, J., Ignatiev, N., Lefevre, F., Olsen, K., Millour, E., Bertaux, J.-L., Shakun, A., Grigoriev, A., Patrakeev, A., Korsa, S., Wilson, C., Forget, F., and Maattanen, A.: The distribution and saturation of water vapor as inferred from ACS during the first Martian year of TGO Science observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17962, https://doi.org/10.5194/egusphere-egu2020-17962, 2020

D2899 |
Hayley Williamson, Robert Johnson, Ludivine Leclercq, and Meredith Elrod

We examine high altitude gravity waves in the upper atmosphere of Mars using the data from the Neutral Gas and Ion Mass Spectrometer (NGIMS) on the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, orbiting Mars since late 2014. Since the Martian atmosphere is very thin it is also highly perturbed and the effects of these perturbations are debated. Therefore, on 252 trajectories through the Martian atmosphere large amplitude, high altitude perturbations seen in the NGIMS database are examined. When the perturbations are organized by column density rather than altitude, the perturbations both peak and dissipate at similar column densities. These perturbations also increase the O/CO2 ratio above that measured for orbits without a significant perturbation. To understand this effect, the perturbations are subsequently categorized by location and found to be roughly consistent with wave activity seen lower in the atmosphere. Because the NGIMS data for each perturbation cannot measure the temperature or long term behavior, we simulate wave propagation using a Direct Simulation Monte Carlo (DSMC) model. The results from such simulations suggest that these perturbations are most likely large amplitude acoustic gravity waves, whose high frequency and fast phase speed allow them to propagate into the Martian exosphere, affecting the diffusive separation of species and depositing heat.

How to cite: Williamson, H., Johnson, R., Leclercq, L., and Elrod, M.: Large amplitude exospheric waves seen in MAVEN NGIMS data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2183, https://doi.org/10.5194/egusphere-egu2020-2183, 2020

D2900 |
Jorge Hernandez Bernal, Agustín Sánchez-Lavega, Teresa del Río-Gaztelurrutia, Ricardo Hueso, Iñaki Ordóñez-Etxeberria, Alejandro Cardesín-Moinelo, Eleni Ravanis, Simon Wood, Dmitrij Titov, Kyle Connour, Nick Schneider, Daniela Tirsch, Ralf Jaumann, Ernst Hauber, and Brigitte Gondet

Starting in September 2018, a daily repeating extremely elongated cloud was observed extending from the Mars Arsia Mons volcano. We study this Arsia Mons Elongated Cloud (AMEC) using images from VMC, HRSC, and OMEGA on board Mars Express, IUVS on MAVEN, and MARCI on MRO. We study the daily cycle of this cloud, showing how the morphology and other parameters of the cloud evolved with local time. The cloud expands every morning from the western slope of the volcano, at a westward velocity of around 150m/s, and an altitude of around 30-40km over the local surface. Starting around 2.5 hours after sunrise (8.2 Local True Solar Time, LTST), the formation of the cloud resumes, and the existing cloud keeps moving westward, so it detaches from the volcano, until it evaporates in the following hours. At this time, the cloud has expanded to a length of around 1500km. Short time later, a new local cloud appears on the western slope of the volcano, starting around 9.5 LTST, and grows during the morning.

This daily cycle repeated regularly for at least 90 sols in 2018, around Southern Solstice (Ls 240-300) in Martian Year (MY) 34. According with these and previous  MEx/VMC observations, this elongated cloud is a seasonal phenomenon occurring around Southern Solstice every Martian Year. We study the interannual variability of this cloud, the influence of the Global Dust Storms in 2018 on the cloud’s properties (Sánchez-Lavega et al., Geophys. Res. Lett. 46, 2019), and its validity as a proxy for the global state of the Martian atmosphere (Sánchez-Lavega et al., J. Geophys. Res., 123, 3020, 2018). We discuss the physical mechanisms behind the formation of this peculiar cloud in Mars.

How to cite: Hernandez Bernal, J., Sánchez-Lavega, A., del Río-Gaztelurrutia, T., Hueso, R., Ordóñez-Etxeberria, I., Cardesín-Moinelo, A., Ravanis, E., Wood, S., Titov, D., Connour, K., Schneider, N., Tirsch, D., Jaumann, R., Hauber, E., and Gondet, B.: Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-433, https://doi.org/10.5194/egusphere-egu2020-433, 2019

D2901 |
Nelly Mouawad, Judy Chebly, François Leblanc, Jonathan Fraine, and Kahil Fatima

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging NASA’s spacecraft, known as MESSENGER, flew by Mercury on September 29, 2009. It was the spacecraft’s third and final flyby, before it went into orbit around the planet. The flyby presented a unique trajectory approach and perspective on the planet’s exosphere, not available when in orbit. We present very high spectral resolution ground-based data obtained at the University of Texas McDonald 2.7-m telescope. These data were acquired within hours of the data taken with the Ultraviolet and Visible Spectrometer (UVVS) onboard MESSENGER. Both datasets targeted similar spatial regions, in the polar altitudes of Mercury. We compare the sodium emissions from both measurements in the exosphere. We find that close to the surface, both intensity measurements match, but the intensities fall off differently with altitude, with the MESSENGER data showing an exponential drop off, sharper than that of the ground-based data; an effect that we attribute to atmospheric seeing. In addition, our ground-based data provided Full Width Half Maximum (fwhm) speeds and Doppler shift speeds; our results suggest energetic processes took place in the polar regions on the dusk side of the planet, but arguably on the dawn side as well. We confirm previous conclusions of Leblanc et al. (2008, 2009) where signatures of energetic processes seem to be coupled with high fwhm speeds and intensity peaks. We compare our Doppler shift velocities with previous works, and find agreement within the uncertainties with Potter et al., (2013) on their transit velocity measurements. Although our peak emissions along the terminator vary in structure and in brightness, they do not exhibit distinctive signatures in the intensity profiles at altitudes above the poles, when compared with convolved MESSENGER space data.

How to cite: Mouawad, N., Chebly, J., Leblanc, F., Fraine, J., and Fatima, K.: Mercury's Na exosphere as seen with very high spectral resolution from the ground, and from space with MESSENGER, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22650, https://doi.org/10.5194/egusphere-egu2020-22650, 2020

D2902 |
Seiko Takagi, Arnaud Mahieux, Valérie Wilquet, Séverine Robert, Ann Carine Vandaele, and Naomoto Iwagami

The Venus cloud consists of a main cloud deck at 47 – 70 km, with thinner hazes above and below.The upper haze on Venus lies above the main cloud surrounding the planet, ranging from the top of the cloud (70 km) up to as high as 90 km.

The Solar Occultation in the InfraRed (SOIR) instrument onboard Venus Express was designed to measure the Venusian atmospheric transmission at high altitudes (65 – 220 km) in the infrared range (2.2 – 4.3 µm) with a high spectral resolution. We investigate the optical properties of Venus’s haze layer above 90 km using SOIR solar occultation observations. Vertical and latitudinal profiles of the extinction coefficient, optical thickness, and mixing ratio of aerosols are retrieved. One of the most remarkable results is that the aerosol mixing ratio tends to increase with altitude above 90 km at both high and low latitude. We speculate how aerosols could be produced at such high altitudes.

How to cite: Takagi, S., Mahieux, A., Wilquet, V., Robert, S., Vandaele, A. C., and Iwagami, N.: An uppermost haze layer above 100 km found over Venus by the SOIR instrument onboard Venus Express, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21185, https://doi.org/10.5194/egusphere-egu2020-21185, 2020

D2903 |
Sebastien Lebonnois, Gabriella Gilli, Diogo Quirino, Vasco Silva, Thomas Navarro, Franck Lefevre, and Anni Määttänen

To investigate the amount of data recently acquired by the Venus Express (VEx) and Akatsuki missions as well as from ground-based telescopes, Venus Global Climate Models (GCM) are powerful tools. Our understanding of the Venusian climate has increased with recent progresses with these models.
The IPSL Venus GCM has been used recently to investigate all regions of the Venusian atmosphere, as it covers the surface up to the thermosphere (150 km). It involves a photochemical module with a simplified cloud scheme that enables the study of the composition and the coupling with the upper atmosphere, where composition plays a crucial role on the non-LTE and EUV heating processes. Other relevant physical processes in the thermosphere (e.g. molecular diffusion and thermal conduction) are taken into account. Below 100 km, the infrared energy budget is computed based on a Net Exchange Rate formalism. The cold collar structure has been modeled when taking into account the latitudinal distribution of the cloud structure. Globally averaged profiles (e.g spatially and temporally) extracted from the state-of-the-art IPSL Venus GCM provide realistic templates of the atmosphere of Venus. 
VEx observations revealed a more variable atmosphere than expected, in particular the “transition” region (~70-120 km) between the retrograde superrotating zonal flow and the day-to-night circulation showed latitude and day-to-day variations of temperature up to 80 K above 100 km at the terminator, and apparent zonal wind velocities measured around 96 km on the Venus nightime highly changing in space and time. Those variations are not fully explained by current 3D models and specific processes (e.g. gravity wave propagation, thermal tides, large scale planetary waves) responsible for driving them are still under investigation. The role of convectively-generated gravity waves and their impact on zonal wind and temperature in the region of aerobraking can be explored with the IPSL-VGCM, thanks to the inclusion of a stochastic non-orographic gravity waves parameterization, based on the Earth GCM. Data-model comparison of distribution of dynamical tracers above the clouds  (e.g O2(1Δ) nightglow, CO and O density) will be crucial to shed a light on a region where no direct wind measurements are available.
Akatsuki’s LIR camera revealed the presence of  planetary-scale mountain waves at the cloud top in the afternoon. Simulations of the upper atmosphere suggest that mountain waves can easily reach the upper atmosphere, to polar latitudes and the nightside, thus affecting atmospheric dynamics as high as 130 km.

How to cite: Lebonnois, S., Gilli, G., Quirino, D., Silva, V., Navarro, T., Lefevre, F., and Määttänen, A.: Exploring the variability of the venusian atmosphere above the clouds with the IPSL Venus GCM, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18583, https://doi.org/10.5194/egusphere-egu2020-18583, 2020

D2904 |
Arnaud Mahieux, Ann Carine Vandaele, Sarah Chamberlain, Valérie Wilquet, Séverine Robert, Arianna Piccialli, Ian Thomas, and Loic Trompet

The Solar Occultation in the InfraRed (SOIR) instrument onboard Venus Express sounded the Venus mesosphere and lower thermosphere at the terminator using solar occultation technique between April 2006 and December 2014.

We report on the water vapor vertical distribution above the clouds and geo-temporal variations, observed during the full Venus Express mission. Water vapor profiles are sampled between 80 and 120 km, and calculations of the water vapor volume mixing ratio agrees with those from previous studies. Short term variations over several Earth days dominate the data set, with densities varying by up to a factor 19 over a 24 hr period. Similarly to what was found for other trace gases detected with the SOIR instrument, such as HCl, HF and SO2, no significant spatial or long term trends are observed.

287 water vapor vertical profiles obtained at the Venus terminator between 80 km and 120 km from August 2006 and September 2014 were analyzed for temporal and spatial abundance variations. Standard deviations are significantly smaller than the full range of volume mixing ratio values at all altitudes indicating that the variations are real.

The decrease in volume mixing ratio abundance below 100 km appears to be a common feature of most water vapor volume mixing ratio profiles and agrees with the decrease in water vapor reported in previous studies. Based on a very limited number of spectra, the variability of the water vapor VMR was found to be higher in the lower than in the upper mesosphere of Venus; this is in agreement with our observations as the standard deviation of the SOIR mean profile is the smallest at 100 km and increases with decreasing altitude.

No significant spatial variations or long term temporal variations are observed in the present data set in which short term variability masks all other possible trends. Our observations agree that short term (between 1 and 10 Earth days) variability is dominant.

We also report on simultaneous observations of the water first isotopologue HDO made by SOIR, which occurred 194 times during the whole VEx mission. Similarly to water vapor, we observe a large variation of HDO with time and space, without any clear time of spatial dependency.

We report on the ratio of the simultaneously measured HDO and H2O profiles, that show a constant ratio of 0.1 ± 0.1 below 100 km, and increase exponentially at higher altitude to reach a value of 1 ± 0.4 at 120 km of altitude. The results are in agreement with previous works below 100 km.

How to cite: Mahieux, A., Vandaele, A. C., Chamberlain, S., Wilquet, V., Robert, S., Piccialli, A., Thomas, I., and Trompet, L.: Mesospheric water vapor and D/H ratio at the Venus terminator from SOIR/VEx, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11323, https://doi.org/10.5194/egusphere-egu2020-11323, 2020

D2905 |
Ekaterina Starichenko, Denis Belyaev, Alexander Medvedev, Anna Fedorova, Oleg Korablev, Franck Montmessin, and Alexander Trokhimovskiy

Atmospheric gravity waves (GW) are periodic oscillations of air masses that manifest themselves as fluctuations of density, temperature, pressure and other quantities. Studying vertical distributions of density and temperature helps to characterize vertical propagation of GWs and evaluate their influence on the coupling between atmospheric layers.

We report on the first results of GWs retrievals in the Martian atmosphere from the solar occultation experiment performed by the Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter TGO [1]. This is the first time when GWs were measured simultaneously in almost the entire atmosphere. The ACS is a set of infrared spectrometers operating on the orbit of Mars since April 2018. The mid-infrared channel (ACS-MIR) is a cross-dispersion spectrometer covering the 2.3–4.2 µm spectral range with the resolving power reaching ~30 000. In the solar occultation mode the spectrometer can observe thin layers of the Martian thermosphere and lower atmosphere in strong (e.g. 2.7 and 4.3 μm) and weak (about 3 μm) CO2 absorption bands with vertical resolution ~1 km. The near-infrared channel (ACS-NIR) is another echelle spectrometer working in the 0.73–1.6 µm spectral range with the resolving power ~25000 [2]. Due to the high resolution, these instruments (operating simultaneously) allow for deriving the temperature, pressure and density fluctuations at the unprecedented altitude range from 10 to 180 km. The dataset we present consists of more than 100 vertical profiles derived at seasons from the second half of MY34 to the beginning of MY35 in the both Martian hemispheres. The data analysis in IKI is supported by the RSF grant #20-42-09035.



[1] Korablev O. et al., 2018. The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev., 214:7. DOI 10.1007/s11214-017-0437-6.

[2] Fedorova A. et al., 2020. Stormy water on Mars: The distribution and saturation of atmospheric water during the dusty season. Science, eaay9522. DOI: 10.1126/science.aay9522.

How to cite: Starichenko, E., Belyaev, D., Medvedev, A., Fedorova, A., Korablev, O., Montmessin, F., and Trokhimovskiy, A.: Characterization of the atmospheric gravity waves on Mars at altitudes 10-180 km as measured by the ACS/TGO solar occultations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18609, https://doi.org/10.5194/egusphere-egu2020-18609, 2020

D2906 |
Denis Belyaev, Anna Fedorova, Alexander Trokhimovskiy, Oleg Korablev, Franck Montmessin, Juan Alday, Kevin S. Olsen, and Miguel Lopez-Valverde

The mid-infrared channel of the Atmospheric Chemistry Suite (ACS-MIR) is a cross-dispersion echelle spectrometer dedicated to solar occultation measurements in the 2.3–4.3 μm wavelength range [1]. The instrumental resolving power λ/Δλ reaches ~30 000, while the altitude resolution is ~1 km. ACS-MIR began regular science operations in April 2018 on board the ExoMars Trace Gas Orbiter (TGO). Each occultation session covers a spectral interval with one or a few CO2 absorption bands appropriate for the atmospheric density and temperature retrievals.

In this paper, we present results from data analysis in the 2.65-2.7 μm spectral range hosting strong CO2 absorption bands detectable up to 180 km. It provides us with unprecedented capability to profile CO2 from 20 to 180 km, covering the troposphere, the mesosphere and the thermosphere of Mars. The homopause is found around ~130 km and CO2 mixing ratio decreases from 96% to 20-40% at 180 km due to photolysis and molecular diffusion. A multiple iteration scheme was applied to retrieve CO2 density and temperature from the rotational absorption lines, while pressure was estimated assuming hydrostatic equilibrium. The vertical profiles coincide well with the simultaneous occultations performed below 100 km by the near-infrared channel ACS-NIR [2]. At the moment, our MIR channel dataset is made of >100 profiles encompassing the second half of MY34 and the beginning of MY35 in both martian hemispheres. The retrievals of density/temperature profiles in IKI are funded by the RSF grant #20-42-09035.


[1] Korablev O. et al., 2018. The Atmospheric Chemistry Suite (ACS) of three spectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev., 214:7. DOI 10.1007/s11214-017-0437-6.

[2] Fedorova A. et al., 2020. Stormy water on Mars: The distribution and saturation of atmospheric water during the dusty season. Science, eaay9522. DOI: 10.1126/science.aay9522.

How to cite: Belyaev, D., Fedorova, A., Trokhimovskiy, A., Korablev, O., Montmessin, F., Alday, J., Olsen, K. S., and Lopez-Valverde, M.: Temperature and CO2 density distribution in Mars upper atmosphere from the ACS-MIR / TGO solar occultations at 2.7 μm absorption band, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18371, https://doi.org/10.5194/egusphere-egu2020-18371, 2020

D2907 |
Alexander Trokhimovskiy, Valery Perevalov, Oleg Korablev, Anna Fedorova, Kevin S. Olsen, Jean-Loup Bertaux, Franck Montmessin, Franck Lefèvre, Andrey Patrakeev, and Alexey Shakun

The CO2-dominated atmosphere of Mars is an ideal natural laboratory to study the spectroscopy of this gas. The Atmospheric Chemistry Suite (ACS) package onboard the ExoMars 2016 Trace Gas Orbiter (TGO) sounds the atmosphere in solar occultation, allowing, in case of a very clear atmosphere, reaching an optical path of 300-400 km at an effective pressure of a few millibars. During the first year of ACS observations, the focus of attention was kept on the spectral range covering the fundamental methane absorption band, 2900-3300 cm–1. No methane was detected, while a further improvement of the data processing led to the identification of weak periodic absorption lines, missing from spectroscopic databases. The observed frequencies of the lines match theoretically computed positions of the Q, P and R branches of the magnetic dipole 01111-00001 absorption band of the main CO2 isotopologue, never measured or computed before. We will report the first observational evidence of a magnetic dipole CO2 absorption. The data analysis was supported by RSF (project No. 20-42-09035).

How to cite: Trokhimovskiy, A., Perevalov, V., Korablev, O., Fedorova, A., Olsen, K. S., Bertaux, J.-L., Montmessin, F., Lefèvre, F., Patrakeev, A., and Shakun, A.: First observation of the magnetic dipole CO2 main isotopologue absorption band at 3.3 µm in the atmosphere of Mars by ACS ExoMars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17433, https://doi.org/10.5194/egusphere-egu2020-17433, 2020

D2908 |
Jean-Yves Chaufray, Majd Mayyasi, Michael Chaffin, Justin Deighan, Dolon Bhattacharyya, John Clarke, Sonal Jain, Nick Schneider, and Bruce Jakosky

The recent observations performed with the high-resolution “echelle mode” by the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission indicated large deuterium brightness near Ls=270°. The deuterium brightness observed at the beginning of the mission, when Mars was close to its perihelion show brightness ~ 1 kR much larger than the first deuterium detection from Earth ~ 20-50R in 20-21 January 1997 (Ls = 67°). This low brightness of the deuterium emission is consistent with the lack of deuterium observation with the echelle mode of IUVS at solar longitudes around aphelion (Ls = 71°). During southern summer (Ls = 270°), especially near the terminator, the Lyman-α emission observed at 121.6 nm with the “low resolution mode” presents some vertical profiles that were not reproducible with models including only the emission from the thermal hydrogen population. In this study, we investigate the possibility to derive quantitative information on the D/H ratio at Mars from the vertical Lyman-α profiles observed with the “low resolution mode”, and the main limits of the method.

How to cite: Chaufray, J.-Y., Mayyasi, M., Chaffin, M., Deighan, J., Bhattacharyya, D., Clarke, J., Jain, S., Schneider, N., and Jakosky, B.: Estimate of the D/H ratio in the Martian upper atmosphere from the low spectral resolution mode of MAVEN/IUVS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13984, https://doi.org/10.5194/egusphere-egu2020-13984, 2020

D2909 |
Megan Brown, Manish Patel, Stephen Lewis, and Amel Bennaceur

This project maps ozone and ice-water clouds detected in the martian atmosphere to assess the atmospheric chemistry between ozone, water-ice and hydroxyl radicals. Hydroxyl photochemistry may be indicated by a non-negative or fluctuating correlation between ozone and water-ice. This will contribute to understanding the stability of carbon dioxide and atmospheric chemistry of Mars.

Ozone (O3) can be used for tracking general circulation of the martian atmosphere and other trace chemicals, as well as acting as a proxy for water vapour. The photochemical break down of water vapour produces hydroxyl radicals known to participate in the destruction of ozone. The relationship between water vapour and ozone is therefore negatively correlated. Atmospheric water-ice concentrations may also follow this theory. The photochemical reactions between ozone, water-ice clouds and hydroxyl radicals are poorly understood in the martian atmosphere due to the short half-life and rapid reaction rates of hydroxyl radicals. These reactions destroy ozone, as well as indirectly contributing to the water cycle and stability of carbon dioxide (measured by the CO2–CO ratio). However, the detection of ozone in the presence of water-ice clouds suggests the relationship between them is not always anti-correlated. Global climate models (GCMs) struggle to describe the chemical processes occurring within water-ice clouds. For example, the heterogeneous photochemistry described in the LMD (Laboratoire de Météorologie Dynamique) GCM did not significantly improve the model. This leads to the following questions: what is the relationship between water-ice clouds and ozone, and can the chemical reactions of hydroxyl radicals occurring within water-ice clouds be determined through this relationship?

This project aims to address these questions using nadir and occultation retrievals of ozone and water-ice clouds, potentially using retrievals from the UVIS instrument aboard NOMAD (Nadir and Occultation for Mars Discovery), ExoMars Trace Gas Orbiter. Analysis will include temporal and spatial binning of data to help identify any patterns present. Correlation tests will be conducted to determine the significance of any relationship at short term and seasonal scales along a range of zonally averaged latitude photochemical model from the LMD-UK GCM will be used to further explore the chemical processes.

Interactions between hydroxyl radicals and the surface of water-ice clouds are poorly understood. Ozone abundance is greatest in the winter at the polar regions, which also coincides with the appearance of the polar hood clouds. The use of nadir observations will enable the comparison between total column of ozone abundance at high latitudes (>60°S) in a range of varying water-ice cloud opacities, as well as the equatorial region (30°S – 30°N) during aphelion. Water-ice clouds may remove hydroxyl radicals responsible for the destruction of ozone and thus the previously assumed anticorrelation between ozone and water-ice will not hold. The project will therefore assess the hypothesis that: water-ice clouds may act as a sink for hydroxyl radicals.

How to cite: Brown, M., Patel, M., Lewis, S., and Bennaceur, A.: Investigating the relationship between ozone and water-ice in the martian atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20354, https://doi.org/10.5194/egusphere-egu2020-20354, 2020

D2910 |
Emily Ball, Dann Mitchell, William Seviour, Geoffrey Vallis, and Stephen Thomson

The Martian winter polar vortex has recently been shown to be annular in nature, with a local minimum in potential vorticity near the pole. This suggests barotropic instability, yet the vortex is remarkably persistent. It has been shown that its annular nature may be due to the release of latent heat from CO2 condensation, CO2 clouds, changes in dust distributions, and the strength of the Hadley circulation circulation, with many of these being interlinked. In this poster, we present results using the the Mars Analysis Correction Data Assimilation (MACDA) reanalysis dataset, which demonstrates clearly the annular vortex. Additionally, we perform simulations of the Martian atmosphere and its response to varying topography and radiation scheme in the flexible Isca framework, a climate model capable of simulating the Martian basic state at varying levels of complexity. It is noted that the strength of the Martian polar vortex is significantly lower in Isca simulations than in the MACDA dataset. Through further simulations with Isca, we aim to investigate the effect of CO2 condensation on the strength and shape of the Martian polar vortex.

How to cite: Ball, E., Mitchell, D., Seviour, W., Vallis, G., and Thomson, S.: Mars' Annular Polar Vortex, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10361, https://doi.org/10.5194/egusphere-egu2020-10361, 2020

D2911 |
Michael Kurgansky

Dust devils play a major role on Mars, providing a significant proportion of the total dust removal from the surface and its injection into the atmosphere, thus largely determining the overall radiative regime and the climatic state of the Martian atmosphere. The amount of dust lifted to the atmosphere by a population of dust devils is determined by the number density of dust devils (their number per unit area) and by their size-frequency and intensity-frequency distributions. Using the Abel transform, a two-step methodology has been developed to determine the marginal statistical distributions of convective vortices, including dust devils, on their intensity (pressure drop in the vortex center) and size (diameter), based on statistics of transient pressure drops recorded when the vortices pass near a pressure sensor placed on the surface of the planet. In a first step, if the pressure profile within the vortex is realistically modeled then the intensity-frequency distribution in the population of vortices can be inferred from the statistics of peak pressure drops recorded alone. If the observed statistics can be approximated with a truncated power-law distribution and in the absence of an apparent correlation between the vortex diameter and the maximum pressure drop at its center, then the measurements provide an unbiased power-law estimate of the actual intensity-frequency distribution. In a second step and in a practically important case when the distribution of vortices on their intensity follows the power law, the problem of determining the vortex size-frequency distribution is solved from data obtained in pressure time-series surveys. This two-step technique has been applied with success to Mars Science Laboratory (MSL) convective vortices.

This work was supported by the Presidium of the Russian Academy of Sciences, project no. 19-270. The method of inferring the vortex size-frequency distribution was developed with the support from the Russian Science Foundation (grant no. 18-77-10076).


Kurgansky M.V. On the statistical distribution of pressure drops in convective vortices: Applications to Martian dust devils // Icarus. Volume 317, 1 January 2019, Pages 209-214. https://doi.org/10.1016/j.icarus.2018.08.004.

Kurgansky M.V. On determination of the size-frequency distribution of convective vortices in pressure time-series surveys on Mars // Icarus. Volume 335, 1 January 2020, 113389. https://doi.org/10.1016/j.icarus.2019.113389.

How to cite: Kurgansky, M.: On Determination of the Intensity and Size Frequency Distribution of Convective Vortices: Applications to Martian Dust Devils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1738, https://doi.org/10.5194/egusphere-egu2020-1738, 2019

D2912 |
Lorenz Roth, Gabriel Giono, Nickolay Ivchenko, Joachim Saur, Kurt Retherford, Darrell Strobel, Stephan Schlegel, and Marcus Ackland

After evidence for present-day geological activity on Jupiter’s moon Europa remained elusive for decades, several recent studies derived the existence of plumes on various locations. We have re-analyzed the three HST/STIS transit images in which Sparks et al. (2016) identified limb anomalies as evidence for Europa’s plume activity. After reproducing the results of Sparks et al. (2016), we find that positive outliers are similarly present in the images as the negative outliers that were attributed to plume absorption. A physical explanation for the positive outliers is missing. We identify two factors that affect the significance of the measured outliers in the region above Europa’s limb: The exact location of Europa on the detector and the description of the statistical fluctuations in the images. When accounting for these factors, the statistical significance of the plume candidate features is about 3 sigma or lower in the three images. The resulting positive and negative outliers are consistent with random statistical occurrence in a sample size given by the number of pixels in Europa's limb region.

How to cite: Roth, L., Giono, G., Ivchenko, N., Saur, J., Retherford, K., Strobel, D., Schlegel, S., and Ackland, M.: Re-analysis of limb anomaly detections in three HST/STIS transit images of Europa: No evidence for plumes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17846, https://doi.org/10.5194/egusphere-egu2020-17846, 2020

D2913 |
Kostas Tsigaridis, Anthony D. Del Genio, Igor Aleinov, Eric T. Wolf, Maxwell Kelley, Michael J. Way, Linda E. Sohl, and Reto A. Ruedy

Understanding the climate of terrestrial planetary atmospheres has been increasingly the focus of research worldwide, in light of the increasing amount of rocky planet discoveries orbiting other stars in or near their habitable zone. Here we present simulations with the new version of the 3D climate model ROCKE-3D, whose version 2.0 will soon become publicly available. A wide range of configurations will be supported, compared to a handful ones in its predecessor, version 1.0 (Way et al., 2017). These include two model resolutions (4x5 and 2x2.5), two radiation schemes (GISS and SOCRATES), three atmospheric configurations (Earth-like, Earth-like without O3 and aerosols, and N2-dominated), and three ocean setups (prescribed sea-surface temperatures and ice cover, q-flux, and dynamic). Simulations of all different configuration combinations have been performed and will become available for use by the community. Key results will be presented across those configurations, together of the role of the structural uncertainty in model setup in the resulting climate calculated by the model.

How to cite: Tsigaridis, K., Del Genio, A. D., Aleinov, I., Wolf, E. T., Kelley, M., Way, M. J., Sohl, L. E., and Ruedy, R. A.: 3D climate simulations of Earth-like planets with a range of atmospheric composition, radiative transfer, ocean, and resolution configurations, using the new version of ROCKE-3D, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8892, https://doi.org/10.5194/egusphere-egu2020-8892, 2020

D2914 |
David Goldstein, Arnaud Mahieux, Philip Varghese, and Laurence Trafton

The two-phase water plumes arising from the Enceladus South pole and extending hundreds of km from the moon are a key signature of what lies below the surface. Multiple Cassini instruments measured the gas-particle plume over the warm Tiger Stripe region during several close flybys. A lot of work has been put into constraining the vent and flow characteristics, such the vent positions and orientations, the mass flows, speeds and temperatures.
The most likely source for these extensive geysers is a subsurface liquid reservoir of somewhat saline water and oth-er volatiles boiling off through crevasse-like conduits into the vacuum of space. The plumes thus provide a window for understanding Enceladus’ subsurface composition and geysering.
We used a DSMC code to simulate the plume, as it exits a vent, under axisymmetric conditions, in a vertical domain extending up to 10 km, where the flows become collisionless. We performed a DSMC parametric study of the flow parameters considering the following eight parameters: vent diameter, outgassed flow density, water vapor/ice mass ratio, gas and ice speed, ice grain diameter, temperature and vent exit angle.
We constructed parametric expressions for the plume characteristics – number density, temperature, velocity compo-nents – using simple analytic expressions to depict the constrained surfaces of these parameter values, at the 10 km upper boundary.
We use these parametrizations to propagate the plumes to higher altitudes – up to thousands of km – assuming free-molecular conditions. The density field at higher altitude is determined from the parametrizations described above, and explicit analytical expressions for the various force fields that the plumes are experiencing: Enceladus and Saturn gravity fields, Coriolis and centripetal accelerations due to Enceladus rotation.
This split domain approach enables rapid numerical computations – ~10 minutes – and tabulations of the density and velocity fields in space.
We then performed a formal Monte Carlo sensitivity analysis of twelve vent parameters – the ones cited above plus vent latitude, longitude, azimuth and zenith angles of the venting direction – conditioned on the number density field measured by the INMS instrument, considering the 98-vent geometry reported in Porco et al. (2014). The sensitivity analysis is used to determine which vent parameters should be considered for a subsequent fit of the INMS observa-tion. We present an advanced way to constrain the vent parameters by performing a Markov Chain Monte Carlo search that returns probability values for the preselected vent parameters, considering a few INMS observations. This ap-proach allows us to constrain many vent parameters (up to a few hundreds), and, uniquely, return probability distri-bution for each of them.

How to cite: Goldstein, D., Mahieux, A., Varghese, P., and Trafton, L.: Enceladus geyser study using Markov Chain Monte Carlo fits of DSMC simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11502, https://doi.org/10.5194/egusphere-egu2020-11502, 2020

D2915 |
Kevin Douglas, Thomas Mangan, Jaun Diego Carrillo-Sanchez, David Bones, Wuhu Feng, Mark Blitz, and John Plane

             Phosphorus, P, is a key biological element with major roles in replication, information transfer, and metabolism. Interplanetary dust particles (IDPs) contain ~0.8 % P by elemental abundance, and meteoric ablation in a planetary atmosphere is a significant source of atomic P. Orthophosphate (oxidation state +5) is the dominant form of inorganic P at the Earth’s surface, however, due to their low water solubility and reactivity, such P(V) salts have a poor bio-availability. Less oxidised forms of P (oxidation state ≤ +3) are however far more bio-available. Previous studies have focused on the direct delivery of P to the surface in meteorites. In contrast, the atmospheric chemistry of P has so far been ignored.

            The vaporized P atoms entering the upper atmospheres of the terrestrial planets will undergo chemical processing to form a variety of compounds in which P may exist in different oxidation states due to the presence of both oxidizing and reducing agents. Initial oxidation of P will proceed to produce PO2. From PO2, an exothermic route to phosphoric acid (H3PO4) exists via the formation of HOPO2; however, the bio-available compound phosphonic acid (H3PO3) should also form via HPO2.

            Using a combination of both experiment and theory, rate coefficients for the reactions of meteor ablated P have been determined. Using a pulsed laser photolysis-laser induced fluorescence (LIF) technique, the reactions of P, PO, and PO2 with atmospherically relevant species have been studied as a function of temperature for the first time. Rate coefficients for the subsequent reactions of PO2 leading onto to phosphoric and phosphonic acid were calculated from high-level electronic structure calculations.

            In addition to understanding the reaction kinetics, the delivery of P to the upper atmospheres of Earth, Mars, and Venus via the ablation of IDPs has also been investigated. Using a meteor ablation simulator, micron-size particles were flash heated, and the ablation of PO and Ca recorded simultaneously by LIF. These ablation profiles were used to validate the output of a Chemical Ablation Model (CABMOD), a thermodynamic model that predicts the ablation rates of different elements from IDPs. By combining CABMOD with an astronomical model of dust sources, the global injection rates of P into the atmospheres of Earth, Mars, and Venus has been estimated to be 0.017, 1.15×10-3, and 0.024 t d-1 (tonnes per Earth day) respectively.

            The results from the kinetics experiments, together with the P injection rates from CABMOD, have been input into a global chemistry-climate model of the Earth’s atmosphere (WACCM). Using WACCM, the relative amounts of phosphoric and phosphonic acid produced from meteor ablated P in the Earth’s atmosphere can be assessed. Preliminary results indicated that both H3PO4, and the bio-available H3PO3 are formed, with around a third of the ablated P ending up as H3PO3. Further work is also underway to determine where on the Earth’s surface H3PO3 will be deposited, to understand how accretion rates would have differed on the early Earth, and to input the P chemical scheme into a Mars atmospheric model.

How to cite: Douglas, K., Mangan, T., Carrillo-Sanchez, J. D., Bones, D., Feng, W., Blitz, M., and Plane, J.: Meteor Ablated Phosphorus as a Source of Bioavailable P to the Terrestrial Planets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10457, https://doi.org/10.5194/egusphere-egu2020-10457, 2020