PS2.1

EDI
Atmospheres and exospheres of terrestrial planets, satellites, and exoplanets

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.

Co-organized by AS4/ST2
Convener: Arnaud BethECSECS | Co-conveners: Arianna Piccialli, Jan Vatant d'OlloneECSECS
vPICO presentations
| Thu, 29 Apr, 09:00–11:45 (CEST)

vPICO presentations: Thu, 29 Apr

Chairpersons: Arnaud Beth, Arianna Piccialli
Experiments
09:00–09:02
|
EGU21-8424
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ECS
Illia Zymak, Arnaud Sanderink, Bertrand Gaubicher, Jan Žabka, Jean-Pierre Lebreton, and Christelle Briois

In situ composition measurements at Saturn and its moons (Cassini-Huygens1,2) and at comet 67P/Churyumov-Gerasimenko (Rosetta3,4) unveiled the complexity of the atmospheric chemical composition and high abundance of organic compounds in the environments of Solar System bodies. The deciphering of the measurements, obtained by current state-of-the-art instruments, to obtain the composition of complex gas mixtures that include polyatomic molecules and volatile organic compounds (VOCs) often requires having recourse to instrument response modeling supplemented by theoretical chemical models.

One of the limitations in currently flown mass spectrometers is their limited mass resolving power. High mass-resolving power offers the capability to identify unambiguously almost all complex organic compounds. Such technique offers identification of almost all complex organic compounds without application of complementary separation techniques, e.g. chromatography, spectroscopy or collision induced dissociation. A new generation of space mass spectrometers under development (MASPEX5, MULTUM6, CORALS7, CRATER7, among others), aims at reaching mass resolution of > 50 000. CORALS and CRATER are Orbitrap-based instruments using CosmOrbitrap elements.

In collaboration with J. Herovsky institute, the Laboratoire de Physique et de Chimie de l'Environnement et de l'Espace (LPC2E) has developed a new laboratory test-bench based on the Orbitrap™ technology OLYMPIA (Orbitrap anaLYseur MultiPle IonisAtion) to evaluate several space applications of an Orbitrap-based space instrument using different ionization techniques. OLYMPIA is a compact, transportable set-up and is intended to be used as a stand-alone device (currently with an EI ionization source), but later intended to be coupled to different sources of ions. The next step in the next few months is to couple it with the LLILBID set-up in Berlin8.

OLYMPIA is currently directly coupled with a first prototype of a compact electron impact ionization source. A single shot provides a useful signal duration of 200-250ms second before it decays to the noise level, and provide mass resolution for Kr ion isotopes of the order of 30 000 and on C2H4 on fragments of the order of 40 000. Kr is mostly being used to characterize the isotopic measurement capability of OLYMPIA and mixtures of C2H4, CO and N2gases in different proportions.  In this presentation we concentrate on the capability to detect low ethylene lighter VOC concentration in different mixtures of CO and N2. Sensitivity of the instrument is sufficient to detect traces of the carbon dioxide gas in mixture with molecular nitrogen abundant in less than 1% volume ratio.

1 Waite, J. H. et al. Space Sci. Rev. 114, 113–231 (2004)

2 Coates, A. J. et al. Geophys. Res. Lett. 34, (2007)

3 Balsiger, H. et al. Space Sci. Rev. 128, 745–801 (2007)

4 Le Roy, L. et al. A&A 583, (2015)

5 Brockwell, T. G. et al. in 2016 IEEE Aerospace Conference 1–17 (2016)

6 Shimma, S. et al. Anal. Chem. 82, 8456–8463 (2010)

7 Arevalo Jr, R. et al. Rapid Commun. Mass Spectrom. 32, 1875–1886 (2018)

8 Klenner, F. et al. Astrobiology 20, 179–189 (2019)

How to cite: Zymak, I., Sanderink, A., Gaubicher, B., Žabka, J., Lebreton, J.-P., and Briois, C.: OLYMPIA - a compact laboratory Orbitrap-based high-resolution mass spectrometer laboratory set-up: Performance studies for gas composition measurement in analogues of planetary environments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8424, https://doi.org/10.5194/egusphere-egu21-8424, 2021.

09:02–09:04
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EGU21-10036
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ECS
Peter Haun, Florian Zaussinger, Peter Szabo, and Christoph Egbers

AtmoFlow is the third spherical shell experiment designed to investigate planetary flow structures under microgravity conditions. It is in fact the subsequent investigation of a series of experiments on the ISS namely GeoFlow I and GeoFlow II which investigated mantle convection with and without volumetric heating. As the name already indicated the AtmoFlow experiment is designed for the purpose to investigate atmospheric flow structures and their sensibility of changes in the thermal boundary conditions. The experiment is designed to reveal the influence of melting polar ice caps, the role of the baroclinic jet stream and thus on global climate change.

 

In general, there are three main challenges in constructing such an experiment. First, a radial force field is required which surrogates the buoyancy force under micro gravity conditions. Second, the thermal boundary conditions are non-uniform accordingly to the temperature distribution on earth’s surface, with features as cold North and South Pole as well as a hot equatorial zone. The third challenge considers the measurement technique and the restriction to the flow visualisation which has to rely on non-invasive methods, without particles.

 

A radial force field, similar to the earth gravity is established between both spherical boundaries by applying an alternating electric potential. Thus, the experiment can be considered as a spherical capacitor. Buoyancy may than be expressed via an electric force term, the dielectrophoretic force and is in fact an equivalent term to the Archimedean buoyancy for thermo-electrohydrodynamic convection. An electric Rayleigh number may than be formulated which is comparable to the well-known Rayleigh number formulated by Lord Rayleigh.

In order to fulfil the requirements of the thermal boundary conditions, the experiment is thermalised by a heating circuit for the inner sphere and a cooling circuit for each pole, respectively.

The visualization of the thermal flow between both spherical shells is achieved by a Wollaston shearing interferometry (WSI) unit. This method is able to provide high resolved information of the temperature difference between both shells. However, the system is difficult to align and adjust. Results may also be difficult to interpret as reference cases are missing. For this purpose, we are conducting complementary numerical investigations and ground experiments to fully resolve the recorded images of the AtmoFlow project.

 

In combining experimental and numerical investigations one will obtain a better understanding of the physical process in thermo-electric convection. When the experiment is sent to the ISS, we expect to observe various flow structures with temporal evolution to investigate zonal flow fields, their implication on global weather formation and climate.

How to cite: Haun, P., Zaussinger, F., Szabo, P., and Egbers, C.: AtmoFlow - Investigating planetary fluid flow on the International Space Station, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10036, https://doi.org/10.5194/egusphere-egu21-10036, 2021.

09:04–09:06
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EGU21-13639
|
ECS
Martin Airey, Giles Harrison, Karen Aplin, and Christian Pfrang

Cosmic rays cause ionisation in all planetary atmospheres. As they collide with particles in the atmosphere, secondary charged particles are produced that lead to the formation of cluster ions. The incident cosmic ray flux and atmospheric density of the atmosphere in question determine a profile of ion production rate. From the top of the atmosphere to the planetary surface, this rate increases with atmospheric density to a point where the flux becomes attenuated such that the rate then decreases, resulting in a peak ion production rate at some height known as the Pfotzer-Regener maximum. When these ions interact with aerosols and cloud particles, a net charge results on those particles and this is known to affect their microphysical attributes and behaviour. For example, charging may enable the activation of droplets at lower saturation ratios and also enhance collision efficiency and droplet growth. This becomes important when clouds occur at a height where ionisation is sufficient to have a substantive charging effect on the cloud particles. This has very little direct effect on Earth as peak ion production occurs high above the clouds at 15-20 km; however, on Venus for example the Pfotzer-Regener maximum occurs at ~63 km, coinciding with the main sulphuric acid cloud deck. In situations such as this, the direct result of cloud charging due to cosmic ray induced ionisation may strongly influence cloud processes, their occurrence, and behaviour.

This work uses laboratory experiments to explore the effects of charging on cloud droplets. Individual droplets are levitated in a vertical acoustic standing wave and then monitored using a CCD camera with a high magnification objective lens to determine the droplet lifetime and evaporation rate. Experiments were conducted using both the droplets’ naturally occurring charge as well as some where the region around the drop was initially flooded with ions from an external corona source. The polarity and charge magnitude of the droplets was determined by applying a 10 kV/m electric field horizontally across the drop and observing its deflection towards one of the electrodes. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. This occurs when the droplet evaporates until its diameter becomes such that its fissility reaches the threshold at which the instability occurs. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. Therefore, where enhanced ionisation occurs in the presence of clouds the end result may be to reduce droplet stability.

How to cite: Airey, M., Harrison, G., Aplin, K., and Pfrang, C.: Effects of ionisation on cloud behaviour in planetary atmospheres, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13639, https://doi.org/10.5194/egusphere-egu21-13639, 2021.

Mars
09:06–09:08
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EGU21-9457
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ECS
Christophe Mathé, Anni Määttänen, Joachim Audouard, Constantino Listowski, Ehouarn Millour, François Forget, Aymeric Spiga, Déborah Bardet, Lucas Teinturier, Lola Falletti, Margaux Vals, Franscico González-Galindo, and Franck Montmessin

In the Martian atmosphere, carbon dioxide (CO2) clouds have been revealed by numerous instruments around Mars from the beginning of the XXI century. These observed clouds can be distinguished by two kinds involving different formation processes: those formed during the winter in polar regions located in the troposphere, and those formed during the Martian year at low- and mid-northern latitudes located in the mesosphere (Määattänen et al, 2013). Microphysical processes of the formation of these clouds are still not fully understood. However, modeling studies revealed processes necessary for their formation: the requirement of waves that perturb the atmosphere leading to a temperature below the condensation of CO2 (transient planetary waves for tropospheric clouds (Kuroda et al., 20123), thermal tides (Gonzalez-Galindo et al., 2011) and gravity waves for mesospheric clouds (Spiga et al., 2012)). In the last decade, a state-of-the-art microphysical column (1D) model for CO2 clouds in a Martian atmosphere was developed at Laboratoire Atmosphères, Observations Spatiales (LATMOS) (Listowski et al., 2013, 2014). We use our full microphysical model of CO2 cloud formation to investigate the occurrence of these CO2 clouds by coupling it with the Global Climate Model (GCM) of the Laboratoire de Météorologie Dynamique (LMD) (Forget et al., 1999). We recently activated the radiative impact of CO2 clouds in the atmosphere. Last modeling results on Martian CO2 clouds properties and their impacts on the atmosphere will be presented and be compared to observational data.

How to cite: Mathé, C., Määttänen, A., Audouard, J., Listowski, C., Millour, E., Forget, F., Spiga, A., Bardet, D., Teinturier, L., Falletti, L., Vals, M., González-Galindo, F., and Montmessin, F.: Global 3D modelling of Martian CO2 clouds, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9457, https://doi.org/10.5194/egusphere-egu21-9457, 2021.

09:08–09:10
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EGU21-7617
|
ECS
Emily Ball, Dann Mitchell, William Seviour, Geoffrey Vallis, and Stephen Thomson

Mars’ polar vortices play a mjaor role in determining the global-scale transport of trace gases and the composition of the polar caps. Potential vorticity (PV) is a key quantity in determining their dynamical and transport properties. Mars' winter polar vortices are annular in PV, a direct contrast to Earth’s stratospheric polar vortices, whose PV values increase monotonically towards the poles. Given that a ring of high PV is known to be barotropically unstable, the persistence of this phenomenon in observations, simulations and reanalyses is somewhat surprising. Condensation of atmospheric carbon dioxide at the winter pole has been shown to be necessary to maintain the annulus in Martian Global Circulation Models (MGCM). Dust is also known to be a cause of internal and interannual variability in the polar vortices, but given the relatively few years of observations available, it is not yet fully understood. Here we present results of an attribution study of the driving mechanisms of the northern hemisphere Martian polar vortex. Using a reanalysis dataset and an idealized MGCM, we investigate the combined effects of dust, latent heat release, and topography on the polar vortex.

We show that the vertical PV structure of the polar vortex in the reanalysis is dependent on the observations assimilated, and that high atmospheric dust loading (such as that seen during a global dust storm) can disrupt the vortex and cause the destruction of PV in the low-mid altitudes. We also demonstrate that high dust loading can significantly reduce eddy activity within the core of the vortex over the course of a Martian winter. Latent heat release from carbon dioxide condensation is an important driver of variability within the polar vortex, but it is dust in the model that primarily drives the eddy activity throughout the Martian year.

How to cite: Ball, E., Mitchell, D., Seviour, W., Vallis, G., and Thomson, S.: Drivers of Mars' northern winter polar vortex, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7617, https://doi.org/10.5194/egusphere-egu21-7617, 2021.

09:10–09:12
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EGU21-7918
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ECS
Jorge Hernandez-Bernal, Agustín Sánchez-Lavega, and Teresa Del Río-Gaztelurrutia

In a recent work (Hernández-Bernal et al. 2020) we reported the existence and properties of the AMEC (Arsia Mons Elongated Cloud). This cloud appears every martian year around the southern solstice following a quick daily cycle, it expands up to 1800 km after sunrise and disappears before noon. While in the previous work we made an extensive observational study, a number of questions remain unsolved, including the specific specific set of atmospheric conditions that originates this particular cloud at this moment of the year, and why other near volcanoes do not exhibit analogous clouds. In this work we explore, based on models, the physical conditions of the atmosphere around Arsia Mons, such as temperature gradients, winds, and water vapor distribution, as a first step to try to understand this particular cloud.

References:

Hernández-Bernal, J., Sánchez-Lavega, A., Río-Gaztelurrutia, T. D., Ravanis, E., Cardesín-Moinelo, A., Connour, K., ... & Hauber, E. An Extremely Elongated Cloud over Arsia Mons Volcano on Mars: I. Life Cycle. Journal of Geophysical Research: Planets, DOI: 10.1029/2020JE006517

How to cite: Hernandez-Bernal, J., Sánchez-Lavega, A., and Del Río-Gaztelurrutia, T.: Exploring de formation of the Arsia Mons Elongated Cloud on Mars, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7918, https://doi.org/10.5194/egusphere-egu21-7918, 2021.

09:12–09:14
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EGU21-14926
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ECS
James Holmes, Stephen Lewis, Manish Patel, Michael Chaffin, Eryn Cangi, Justin Deighan, Nicholas Schneider, Shohei Aoki, Anna Fedorova, David Kass, and Ann Carine Vandaele

We investigate the evolving water vapour and hydrogen distribution in the martian atmosphere and their associated effect on hydrogen escape during the Mars Year (MY) 34 C storm (a late winter regional dust storm that occurs every Mars year). Improved calculation of the integrated loss of water throughout Mars‘ history (that is currently not well constrained) is possible through tracking the water loss through time from global simulations constrained by available observations. Through constraining water loss we can provide better insight into planetary evolution.

The Open University modelling group global circulation model is combined with retrievals from the ExoMars Trace Gas Orbiter (temperature and water vapour profiles from the Atmospheric Chemistry Suite and water vapour profiles from the Nadir and Occultation for Mars Discovery instrument) and the Mars Climate Sounder (temperature profiles and dust column) on the Mars Reconnaissance Orbiter. This multi-spacecraft assimilation provides the best possible replication of the evolving lower atmosphere.

The unusually intense dusty conditions during the MY 34 C storm led to increased amounts of water vapour and hydrogen above 80 km compared to a more typical C storm, which had an important impact on the amount of water escaping Mars’ atmosphere. Modelled hydrogen escape rates during the MY 34 C storm peaked at around 1.4 x 109 cm-2 s-1, three times the escape rate calculated in the MY 30 C storm scenario and equivalent to those found during previous global-scale dust storms. The weak MY 30 C storm and strong MY 34 C storm can be seen as a bracketing pair of events and therefore the calculated escape rates represent the interannual variabiity expected during C storm events.

Our results indicate water loss during the C storm event each year is highly variable, and must be considered when calculating the integrated loss of water through Mars’ history.

How to cite: Holmes, J., Lewis, S., Patel, M., Chaffin, M., Cangi, E., Deighan, J., Schneider, N., Aoki, S., Fedorova, A., Kass, D., and Vandaele, A. C.: Enhanced water loss during the Mars Year 34 C storm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14926, https://doi.org/10.5194/egusphere-egu21-14926, 2021.

09:14–09:16
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EGU21-12721
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ECS
Mikhail Luginin, Nikolay Ignatiev, Anna Fedorova, Alexander Trokhimovskiy, Alexey Grigoriev, Alexey Shakun, Franck Montmessin, and Oleg Korablev

Carbon dioxide is the major constituent of the Martian atmosphere. Its seasonal cycle plays an important role in atmospheric dynamics and climate. Formation of the polar CO2 frost deposits results in up to 30% of atmospheric pressure variations as well as in dramatic change in surface reflectance and emissivity. Another case of carbon dioxide condensation is formation of a CO2 clouds that are still poorly studied, despite the fact that they have been observed by a number of instruments [1−6] on the orbit of Mars.

In this work, we will present first results of CO2 clouds observations from a combination of thermal-infrared (1.7−17 µm) and near-infrared (0.7-1.6 µm) spectra measured by TIRVIM and NIR instruments onboard the ExoMars Trace Gas Orbiter (TGO) in solar occultation geometry. These instruments are part of the Atmospheric Chemistry Suite (ACS), a set of three spectrometers (NIR, MIR, and TIRVIM) that is conducting scientific measurements on the orbit of Mars since the spring of 2018 [7].

This work was funded by Russian Science Foundation, grant number 20-42-09035.

References

[1] Montmessin et al. (2006). Subvisible CO2 ice clouds detected in the mesosphere of Mars. Icarus, 183, 403–410. https://doi.org/10.1016/j.icarus.2006.03.015

[2] Montmessin et al. (2007). Hyperspectral imaging of convective CO2 ice clouds in the equatorial mesosphere of Mars. Journal of Geophysical Research, 112, E11S90. https://doi.org/10.1029/2007JE002944

[3] Määttänen et al. (2010). Mapping the mesospheric CO2 clouds on Mars: MEx/OMEGA and MEx/HRSC observations and challenges for atmospheric models. Icarus, 209, 452–469. https://doi.org/10.1016/j.icarus.2010.05.017

[4] McConnochie et al. (2010). THEMIS-VIS observations of clouds in the Martian mesosphere: Altitudes, wind speeds, and decameter-scale morphology. Icarus, 210, 545–565. https://doi.org/10.1016/j.icarus.2010.07.021

[5] Vincendon et al. (2011). New near-IR observations of mesospheric CO2 and H2O clouds on Mars. Journal of Geophysical Research, 116, E00J02. https://doi.org/10.1029/2011JE003827

[6] Jiang et al., (2019). Detection of Mesospheric CO 2 Ice Clouds on Mars in Southern Summer. Geophysical Research Letters, 46(14), 7962–7971. https://doi.org/10.1029/2019GL082029

[7] Korablev 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

How to cite: Luginin, M., Ignatiev, N., Fedorova, A., Trokhimovskiy, A., Grigoriev, A., Shakun, A., Montmessin, F., and Korablev, O.: Observations of CO2 clouds on Mars from TIRVIM and NIR solar occultation measurements onboard TGO, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12721, https://doi.org/10.5194/egusphere-egu21-12721, 2021.

09:16–09:18
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EGU21-10804
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ECS
Tatsuya Yoshida and Kiyoshi Kuramoto

   Mars may have obtained a proto-atmosphere enriched in H2, CH4, and CO during accretion. Such a reduced proto-atmosphere would have been largely lost by hydrodynamic escape, but its flux is highly uncertain. To estimate the evolution of the proto-atmosphere of Mars correctly, an exact escape modeling including exact radiative balance and chemical processes is required partly because those reduced species and their photochemical products may act as an effective coolant that suppresses the escape of atmosphere. Here we develop a one-dimensional hydrodynamic escape model that includes radiative processes and photochemical processes for a multi-component atmosphere and apply to the reduced proto-atmosphere on Mars.

   Under the enhanced XUV flux suggested for young Sun, the escape flux decreases by more than one order of magnitude with increasing the mixing fraction of CH4 and CO  from zero to > 10 % mainly because of the energy loss by radiative cooling by these infrared active chemical molecules. Concurrently, the mass fractionation between H2 and other heavier species becomes to be enhanced. Given that the proto-Mars initially obtained > 10 bar of H2 and carbon species equivalent to 1 bar of CO2 was then left behind after the end of the hydrodynamic escape of H2, the total amount of carbon species lost by hydrodynamic escape is estimated to be equivalent to 20 bar of CO2 or more. Such a severe loss of carbon species may explain the paucity of CO2 on Mars compared to Earth and Venus. If the proto-Mars obtained > 100 bar of H2, the timescale for H2 escape exceeds ~100 Myr. This implies that an atmosphere with reduced chemical compositions allowing the production of organic matter deposits may have been kept on early Mars traceable by geologic records.

How to cite: Yoshida, T. and Kuramoto, K.: Sluggish hydrodynamic escape of early Martian atmosphere with reduced chemical compositions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10804, https://doi.org/10.5194/egusphere-egu21-10804, 2021.

09:18–09:20
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EGU21-12816
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ECS
Flavio Petricca, Gael Cascioli, and Antonio Genova

The analysis of atmospheric radio occultations enables an in-depth investigation of planetary ionosphere and neutral atmospheres, by measuring the radio frequency shift that affects a signal propagating through the medium. A precise characterization of the atmospheric layers requires a thorough processing of the radio tracking data to estimate the thermodynamic properties of the atmosphere and their related uncertainties.

A standard procedure to process radio occultation data requires a preliminary knowledge of the spacecraft trajectory. In this work, we present a technique to retrieve refractivity, density, pressure, and temperature profiles with their associated uncertainties through the analysis of raw radio tracking data occulted by the atmosphere. By integrating the algorithm for radio occultation processing with a Precise Orbit Determination (POD) software, an enhanced reconstruction of the spacecraft trajectory is obtained to recover the frequency shift due to the medium refraction. The resulting radio signal is then processed to yield information regarding atmospheric properties. A Monte Carlo simulation algorithm is also included to provide the formal uncertainties of the estimated parameters.

We applied this technique to radio occultation profiles of the NASA mission Mars Reconnaissance Orbiter (MRO). To validate the method, our estimated atmospheric profiles are compared to the numerical predictions of the Mars Global Reference Atmospheric Model (GRAM) and the Mars Climate Database (MCD).

How to cite: Petricca, F., Cascioli, G., and Genova, A.: Analysis of radio occultation data to determine atmospheric profiles and associated uncertainties , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12816, https://doi.org/10.5194/egusphere-egu21-12816, 2021.

09:20–09:22
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EGU21-5562
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ECS
Dmitry Shaposhnikov, Alexander Medvedev, Alexander Rodin, and Paul Hartogh

Effects of atmospheric gravity waves (GWs) on the global water cycle in the middle and high atmosphere of Mars during the global dust storms (Martian years 28 and 34) have been studied for the first time using a general circulation model. Dust storm simulations were compared with those utilizing the climatological distribution of dust in the absence of a GW parameterization. The dust storm scenarios are based on the observations of the dust optical depth by the Mars Climate Sounder instrument on board Mars Reconnaissance Orbiter. The simulations show that accounting for the influence of GWs leads to a change in the concentration of water vapor in the thermosphere. The most significant effect of GWs is twofold. First, cooling of the thermosphere at the poles leads to a decrease in the water vapor abundance during certain periods. Second, heating in the regions representing the main channels of water supply to the upper atmosphere (the so-called water "pump" mechanism) increases, on the contrary, its concentration. Since the temperature increase provides more intensive atmospheric mixing, and also expands the supply channel through an increase in saturation pressure. The dynamic balance of these basic mechanisms drives the changes in the distribution of water vapor in the upper atmosphere. Dust storms enhance pumping of water vapor into the upper atmosphere. Seasonal differences in the storm occurrences in different years allow for tracking the paths of water vapor transport to the upper atmosphere.

How to cite: Shaposhnikov, D., Medvedev, A., Rodin, A., and Hartogh, P.: Impact of atmospheric gravity waves on the Martian global water cycle during dust storms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5562, https://doi.org/10.5194/egusphere-egu21-5562, 2021.

Venus
09:22–09:24
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EGU21-5515
Sebastien Lebonnois, Ehouarn Millour, Antoine Martinez, Thomas Pierron, Aymeric Spiga, Jean-Yves Chaufray, Franck Montmessin, and Fabrice Cipriani

We have over the years developed a state of the art Venus Global Climate Model (GCM, Lebonnois et al. 2016; Gilli et al. 2017; Garate-Lopez & Lebonnois 2018). With funding from ESA in the context of the preparation of the possible upcoming EnVision mission, we have, in the footsteps of what has been done for Mars with the Mars Climate Database (), built a Venus Climate Database (VCD) based on GCM outputs.

The VCD dataset and software overall enable users to:

- extract atmospheric quantities (temperature, pressure, winds, density, …) from the surface to the exobase (~250km) over a climatological Venusian day.

- to better bracket reality, several scenarios are provided, in order to reflect the possible range of solar activity (Extreme UV input from the Sun) which strongly affects the thermosphere (above ~150km), as well as a realistic range of UV albedo cloud top.

- in addition to a baseline climatology, the VCD software provides statistics (internal short term and day-to-day variability) along with means to add perturbations to represent Venusian weather.

At EGU we will present the VCD and its features, emphasizing how it can be useful for scientific users wanting to compare with their models or analyze observations, and for engineers planning future missions.

How to cite: Lebonnois, S., Millour, E., Martinez, A., Pierron, T., Spiga, A., Chaufray, J.-Y., Montmessin, F., and Cipriani, F.: The Venus Climate Database, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5515, https://doi.org/10.5194/egusphere-egu21-5515, 2021.

09:24–09:26
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EGU21-5025
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ECS
Antoine Martinez, Sébastien Lebonnois, Jean-Yves Chaufray, Ehouarn Millour, and Thomas Pierron

For fifteen years, a Global Climate Model (GCM) has been developed for the Venus atmosphere at Institut Pierre-Simon Laplace (IPSL), in collaboration between LMD and LATMOS, from the surface up to 150 km altitude. Its recent extension up to the exobase (roughly 250 km) within the framework of the VCD project now allows us to simulate the Venusian upper atmosphere and the key atmospheric parameters of the aerobraking phases. The aim of this presentation is to study the evolution of the density of the Venusian upper atmosphere as a function of different parameters such as solar irradiance, latitude, local time and zenith solar angle (SZA), for regions from 130 to 180 km of altitude. We will present here several comparisons of the upper atmosphere of Venus between our model results and a selection of aerobraking data from different missions such as Venus Express, Pioneer Venus and Magellan.

How to cite: Martinez, A., Lebonnois, S., Chaufray, J.-Y., Millour, E., and Pierron, T.: Comparison between IPSL Venus Global Climate Model results and aerobraking data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5025, https://doi.org/10.5194/egusphere-egu21-5025, 2021.

09:26–09:28
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EGU21-3657
Masaru Yamamoto, Takumi Hirose, Kohei Ikeda, and Masaaki Takahashi

General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/swith rates of 0.2–0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.

How to cite: Yamamoto, M., Hirose, T., Ikeda, K., and Takahashi, M.: Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3657, https://doi.org/10.5194/egusphere-egu21-3657, 2021.

09:28–09:30
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EGU21-5999
Sanjay Limaye, Rakesh Mogul, Kevin Baines, Mark Bullock, Charles Cockell, James Cutts, Diana Gentry, James Head, Kandis-Lea Jessup, Vladimir Kompanichenko, Yeon Joo Lee, Richard Mathies, Tetyana Milojevic, Rosalyn Pertzborn, Lynn Rothschild, Dirk Schulze-Makuch, David Smith, and Michael Way

The interest in the possibility of life on Venus is driven not just by curiosity about life originating in another Earth-like environment, but because of the possibility that life may be playing a critical role in the planet’s present, and possibly its past, atmospheric state. The brilliance of Venus in the night sky (as viewed from Earth) is due to its highly reflective cloud cover, about 28 km thick at the equator.  Its spectral albedo is about 90% at wavelengths > 500 nm, but it drops gradually to about 40% around 370 nm before rising slightly at shorter wavelengths.  This albedo drop is due to the presence of several absorbers in the atmosphere and the cloud cover.  A very large fraction of the energy absorbed by Venus is at ultraviolet wavelengths with sulfur dioxide above the clouds contributing to the absorption below 330 nm; however, the identities of the other absorbers remain unknown.  The inability to identify the absorbers that are responsible for determining the radiative energy balance of Venus over the last century is a major impediment to understanding how the planet “works”, a major component of NASA’s efforts in planetary exploration.  Limaye et al. (Astrobiology 18, 1181-1198, 2018) presented a hypothesis suggesting that cloud-based microbial life could be contributors to the spectral signatures of Venus’ clouds, building upon previous suggestions of the possibility of life in the clouds of Venus.

Four interconnected themes for the exploration of Venus as an astrobiology target are: – (i) investigations focused on the likelihood that liquid water existed on the surface in the past leading to the potential for the origin and evolution of life, (ii) investigations into the potential for habitable zones within Venus’ clouds and Venus-like atmospheres, (iii) theoretical investigations into how active aerobiology may impact the radiative energy balance of Venus’ clouds and Venus-like atmospheres, and (iv) application of these investigative themes towards better understanding the atmospheric dynamics and habitability of exoplanets. These themes can serve as a basis for proposed Venus Astrobiology Objectives and suggestions for measurements for future missions, as per the goals and objectives developed by the Venus Exploration Analysis Group (VEXAG), which is sponsored by NASA to plan for the future exploration of Venus.  

A Venus Collection to be published in Astrobiology journal in 2021 will include papers from the  “Habitability of the Venus Cloud Layer”, Moscow (October 2019) workshop. 

How to cite: Limaye, S., Mogul, R., Baines, K., Bullock, M., Cockell, C., Cutts, J., Gentry, D., Head, J., Jessup, K.-L., Kompanichenko, V., Lee, Y. J., Mathies, R., Milojevic, T., Pertzborn, R., Rothschild, L., Schulze-Makuch, D., Smith, D., and Way, M.: Venus, an Astrobiology Target, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5999, https://doi.org/10.5194/egusphere-egu21-5999, 2021.

09:30–10:30
Break
Chairpersons: Arnaud Beth, Arianna Piccialli
11:00–11:02
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EGU21-7453
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ECS
Amethyst Johnson and Karen Aplin

Planetary atmospheric electrification has the potential to damage spacecraft, yet for planets with thick, deep atmospheres such as Venus, the level of electrification remains open to interpretation. Partly due to the difficulty of access and potential hostility to spacecraft, there are limited in-situ observations of deep atmospheres, making terrestrial analogies attractive. One proposed explanation of the observations of near-surface electrification on Venus from sensors on Venera 13 & 14 is a haze of charged aerosol. As the Sahara is an environment with lofted dust that is potentially similar to Venus in terms of atmospheric stability, a simple model was developed estimating a mean aerosol charge based on typical Saharan haze aerosol distributions. Spacecraft surface area and descent speeds were used to estimate the accumulated charge and discharge current measured by the Venera missions, but this model underestimated Venera's electrical measurements by three orders of magnitude. This suggests that an aerosol layer alone cannot explain the charge apparently present in the lower atmosphere of Venus. The simple terrestrial analogy employed may not have been suitable due to the modified pressure and temperature profile affecting the mean free path, ionic mobility and consequently the mean charge. Discrepancies in atmospheric stability and wind patterns must also be evaluated, as the effect of terrestrial wind on aerosol distributions may not be directly applicable to other planets. More detailed calculations of ion-aerosol attachment and re-evaluation of the terrestrial analogy may be able to resolve some these issues, but it looks likely that additional significant sources of charge are required to explain the Venera observations. Triboelectric charging of lofted surface material could exceed charging observed in terrestrial situations, or some unknown atmospheric or non-atmospheric source of charge could have contributed to the Venera electrical measurements. 

How to cite: Johnson, A. and Aplin, K.: Planetary aerosol electrification: Lessons learned from a terrestrial analogy for Venus, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7453, https://doi.org/10.5194/egusphere-egu21-7453, 2021.

11:02–11:04
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EGU21-14528
Yeon Joo Lee, Antonio García Muñoz, Takeshi Imamura, Manabu Yamada, Takehiko Satoh, Atsushi Yamazaki, and Shigeto Watanabe

We show that Venus’ disk-integrated brightness at 283, 365, and 2020 nm is modulated by one or both of two periods of 3.7 and 4.6 days, as observed from the Akatsuki Venus orbiter of JAXA. Their typical amplitudes are <10%, but there are occasional events of 20–40%. We find a clear anti-correlation between UV and 2020-nm signals, implying that the cloud top altitudes (2020 nm) and the abundances of UV absorbers (283 and 365 nm) change simultaneously in the global scale. We note that the detected modulations, and their wavelength dependent signals imply the existence of an atmosphere if detected at an exoplanet. Our results should be useful in future direct imaging of terrestrial exoplanets. More details are shown in our paper (https://doi.org/10.1038/s41467-020-19385-6).

How to cite: Lee, Y. J., García Muñoz, A., Imamura, T., Yamada, M., Satoh, T., Yamazaki, A., and Watanabe, S.: Short-term modulations of Venus’ disk-integrated brightness observed from the Venus orbiter Akatsuki, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14528, https://doi.org/10.5194/egusphere-egu21-14528, 2021.

Airless bodies
11:04–11:06
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EGU21-778
Peter Wurz, Audrey Vorburger, Alfred McEwen, Kathy Mandt, Ashley Davies, Sarah Hörst, and Nicolas Thomas

The Io Volcano Observer (IVO) is a proposed NASA Discovery-class mission (currently in Phase A), that would launch in early 2029, arrive at  Jupiter in the early 2033, and perform ten flybys of Io while in Jupiter's orbit. IVO's mission motto is to 'follow the heat', shedding light onto tidal heating as a fundamental planetary process. Specifically, IVO will determine (i) how and where heat is generated in Io's interior, (ii) how heat is transported to the surface, and (iii) how Io has evolved with time. The answers to these questions will fill fundamental gaps in the current understanding of the evolution and habitability of many worlds across our Solar System and beyond where tidal heating plays a key role, and will give us insight into how early Earth, Moon, and Mars may have worked.

One of the five key science questions IVO will be addressing is determining Io's mass loss via atmospheric escape. Understanding Io's mass loss today will offer information on how the chemistry of Io has been altered from its initial state and would provide useful clues on how atmospheres on other bodies have evolved over time. IVO plans on measuring Io's mass loss in situ with the Ion and Neutral Mass Spectrometer (INMS), a successor to the instrument currently being built for the JUpiter Icy moons Explorer (JUICE). INMS will measure neutrals and ions in the mass range 1 – 300 u, with a mass resolution (M/ΔM) of 500, a dynamic range of > 105, a detection threshold of 100 cm–3 for an integration time of 5 s, and a cadence of 0.5 – 300 s per spectrum.

In preparation for IVO, we model atmospheric density profiles of species known and expected to be present on Io's surface from both measurements and previous modelling efforts. Based on the IVO mission design, we present three different measurement scenarios for INMS we expect to encounter at Io based on the planned flybys: (i) a purely sublimated atmosphere, (ii) the 'hot' atmosphere generated by lava fields, and (iii) the plume gases resulting from volcanic activity. We calculate the expected mass spectra to be recorded by INMS during these flybys for these atmospheric scenarios.

How to cite: Wurz, P., Vorburger, A., McEwen, A., Mandt, K., Davies, A., Hörst, S., and Thomas, N.: Modelling of Io’s Atmosphere for the IVO Mission, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-778, https://doi.org/10.5194/egusphere-egu21-778, 2021.

11:06–11:08
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EGU21-2942
Audrey Vorburger and Peter Wurz

With the pending launches of JUICE and Europa Clipper within the next three years, interest in Europa plumes and the implications they might hold has regained momentum.

In 2014, Roth et al. presented first evidence for Europa plume activity based on Hubble Space Telescope (HST) Space Telescope Imaging Spectograph (STIS) Lyman-alpha and OI 1304 Å line emission observations. The observed line emissions imply two underlying plumic sources, located ~20° apart, exhibiting radial expansions of ~200 km and latitudinal expansions of ~20°, and containing ~2,000 kg of H2O (~1.5 ∙ 1016 H2O/cm2). Since then, several more Europa plume observation attempts were undertaken, though only a hand full proved successful. 

Most importantly, the true nature of the observed plume signature still remains to be determined. Plumes can either originate from the topmost surface layer, from within the ice layer, or from the sub-surface ocean. Depending on the location of origin, the plumes contain information about vastly different zones: If they are surficial, they will contain information about the highly irradiated and highly processed surface, if they originate from the sub-surface ocean, they might hold information on Europa’s potentially life-bearing region.

In this presentation, we present 3D Monte-Carlo model results of three different plume scenarios, two of which originate in Europa’s surface ice layer (near-surface liquid inclusion and diapir) whereas the third originates in the sub-surface ocean (oceanic plume). In this model we trace not only the H2O molecules, but also its dissociation products, i.e., OH, H and O. To compare the plume structures obtained from the Monte-Carlo model to the HST-STIS observations, we include all known relevant Lyman-alpha and OI 1304 Å emission excitation mechanisms in our model. Such a comparison does not only shed more light on the plumes that have already been observed, but will also help targeting plume measurements in the near future, as well as interpreting in situ measurements once such become available.

How to cite: Vorburger, A. and Wurz, P.: 3D Monte-Carlo Model of Europa's Water Plumes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2942, https://doi.org/10.5194/egusphere-egu21-2942, 2021.

Exoplanets
11:08–11:10
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EGU21-10235
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ECS
Dominic Samra, Christiane Helling, Michiel Min, and Til Birnstiel

Exoplanets provide excellent laboratories to explore novel atmospheric regimes; using observations coupled with microphysical models we can probe our understanding of the formation and evolution of planets beyond those in the Solar System. However, clouds remain a key challenge in observation of exoplanet atmospheres, both altering the local atmospheric composition and obscuring deeper atmospheric layers. Currently, most observed exoplanet atmospheres are tidally locked gas-giants in close orbit around their host star. These hot and ultra-hot Jupiters have day-side temperatures in excess of 2500 K, and still above 400 K on the night-side, thus they form solid clouds made of minerals, metal oxides and metals. These clouds may form snowflake like structures, either through condensation or by constructive collisions (coagulation).

We explore the effects of non-compact, non-spherical cloud particles in gas-giant exoplanet atmospheres by expanding our kinetic non-equilibrium cloud formation model, to include parameterised porous cloud particles as well as cloud particle growth and fragmentation through collisions. We apply this model to prescribed 1D temperature - pressure Drift-Phoenix atmospheric profiles, using Mie theory and effective medium theory to study cloud optical depths, representing the effects of the non-spherical cloud particles through a statistical distribution of hollow spheres.

Finally, we apply our cloud formation model to a sample of gas-giants as well as ultra-hot Jupiters, using 1D profiles extracted from the 3D SPARC/MITgcm general circulation model. In particular, we take the example cases of gas-giant WASP-43b and the ultra-hot Jupiter HAT-P-7b, where we find dramatic differences in the day-/night-side distribution of clouds between these types of exoplanets due to the intensity of stellar irradiation for HAT-P-7b. Further an asymmetry in cloud coverage at the terminators of ultra-hot Jupiters is observable in the optical depth of the clouds, which affects the observable atmospheric column and thus has implication for detection of key gas phase species. Clouds also enhance the gas phase C/O which is often used as an indicator of formation history. With next-generation instruments such as the James Webb Space Telescope (JWST) such details will begin to be examined, but we find that a detailed understanding of cloud formation processes will be required to interpret observations.

How to cite: Samra, D., Helling, C., Min, M., and Birnstiel, T.: Modelling Mineral Snowflakes in the Atmospheres of Gas-Giant Exoplanets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10235, https://doi.org/10.5194/egusphere-egu21-10235, 2021.

11:10–11:12
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EGU21-936
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ECS
Patrick Barth, Christiane Helling, Eva E. Stüeken, Vincent Bourrier, Nathan Mayne, Paul B. Rimmer, Moira Jardine, Aline A. Vidotto, Peter J. Wheatley, and Rim Fares

Hot Jupiters provide valuable natural laboratories for studying potential contributions of high-energy radiation to prebiotic synthesis in the atmospheres of exoplanets. HD 189733b, a hot Jupiter orbiting a K star, is one of the most studied and best observed exoplanets. We combine XUV observations and 3D climate simulations to model the atmospheric composition and kinetic chemistry with the STAND2019 network. We show how XUV radiation, cosmic rays (CR), and stellar energetic particles (SEP) influence the chemistry of the atmosphere. We explore the effect that the change in the XUV radiation has over time, and we identify key atmospheric signatures of an XUV, CR, and SEP influx. 3D simulations of HD 189733b's atmosphere with the 3D Met Office Unified Model provide a fine grid of pressure-temperature profiles, consistently taking into account kinetic cloud formation. We apply HST and XMM-Newton/Swift observations obtained by the MOVES programmewhich provide combined X-ray and ultraviolet (XUV) spectra of the host star HD 189733 at 4 different points in time. We find that the differences in the radiation field between the irradiated dayside and the shadowed nightside lead to stronger changes in the chemical abundances than the variability of the host star's XUV emission. We identify ammonium (NH4+) and oxonium (H3O+) as fingerprint ions for the ionization of the atmosphere by both galactic cosmic rays and stellar particles. All considered types of high-energy radiation have an enhancing effect on the abundance of key organic molecules such as hydrogen cyanide (HCN), formaldehyde (CH2O), and ethylene (C2H4). The latter two are intermediates in the production pathway of the amino acid glycine (C2H5NO2) and abundant enough to be potentially detectable by JWST. Ultimately, we show that high energy processes potentially play an important role in prebiotic chemistry.

P Barth et al., MOVES IV. Modelling the influence of stellar XUV-flux, cosmic rays, and stellar energetic particles on the atmospheric composition of the hot Jupiter HD 189733b, Monthly Notices of the Royal Astronomical Society, in press, DOI:10.1093/mnras/staa3989

How to cite: Barth, P., Helling, C., Stüeken, E. E., Bourrier, V., Mayne, N., Rimmer, P. B., Jardine, M., Vidotto, A. A., Wheatley, P. J., and Fares, R.: Modelling the influence of high-energy radiation on the atmospheric composition of the hot Jupiter HD 189733b, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-936, https://doi.org/10.5194/egusphere-egu21-936, 2021.

11:12–11:14
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EGU21-2638
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ECS
Guillaume Chaverot, Emeline Bolmont, Martin Turbet, and Jérémy Leconte

There is a strong interest to study the runaway greenhouse effect [1-4] to better determine the runaway greenhouse insolation threshold and therefore the inner edge of the habitable zone (HZ). Some studies [5-7] have shown that the onset of the runaway greenhouse may be delayed due to an increase of the Outgoing Longwave Radiation (OLR) by adding radiatively inactive gas (e.g. N2 or O2, as in the Earth's atmosphere). For such atmosphere the OLR may “overshoot” the Simpson-Nakajima limit [4], i.e. the moist greenhouse limit of a pure vapor atmopshere. This has direct consequences on the position of the inner edge of the HZ [8-11] and thus on how close the Earth is from a catastrophic runaway greenhouse feedback. The OLR overshoot has previously been interpreted as a modification of the atmospheric profile due to the background gas [7,12]. However there is still no consensus so far in the literature on whether an OLR overshoot is really expected or not.

The first aim of our work is to determine, through sensitivity tests, the main important physical processes and parametrizations involved in the OLR computation with a suite of 1D radiative-convective models. By doing multiple sensitivity experiments we are able to explain the origin of the differences in the results of the literature for a H2O+N2 atmosphere. We showed that physical processes usually assumed as second order effects are actually key to explain the shape of the OLR (e.g., line shape parameters). This work can also be useful to guide future 3D GCM simulations. We propose also preliminary results from the LMD-Generic model to study how these effects may be understand in a 3D simulation.

Secondly we propose a reference OLR curve, done with a 1D model built according to the sensitivity tests, for a H2O+N2 atmosphere, to solve the question of the potential overshoot.

 

References

[1] Komabayasi, M. 1967, Journal of the Meteorological Society of Japan. Ser. II

[2] Ingersoll, A. 1969

[3] Nakajima, S., Hayashi, Y.-Y., & Abe, Y. 1992, Journal of the Atmospheric Sciences

[4] Goldblatt, C. & Watson, A. J. 2012, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences

[5] Goldblatt, C., Claire, M. W., Lenton, T. M., et al. 2009, Nature Geoscience

[6] Goldblatt, C., Robinson, T. D., Zahnle, K. J. et al., 2013, Nature Geoscience

[7] Koll, D. D. B. & Cronin, T. W. 2019, The Astrophysical Journal

[8] Leconte, J., Forget, F., Charnay, B. et al., 2013, Nature

[9] Kopparapu, R. k., Ramirez, R., Kasting, J. F., et al. 2013, The Astrophysical Journal

[10] Ramirez, R. M. 2020, Monthly Notices of the Royal Astronomical Society

[11] Zhang, Y. & Yang, J. 2020, The Astrophysical Journal

[12] Pierrehumbert, R. T. 2010, Principles of planetary climate

 

How to cite: Chaverot, G., Bolmont, E., Turbet, M., and Leconte, J.: How does the background atmosphere affect the onset of the runaway greenhouse? Insights from 1D radiative-convective modeling., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2638, https://doi.org/10.5194/egusphere-egu21-2638, 2021.

11:14–11:16
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EGU21-4855
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ECS
Neil Lewis and Peter Read
Super-rotation is a phenomenon in atmospheric dynamics where the specific axial angular momentum of the wind (at some location) in an atmosphere exceeds that of the underlying planet at the equator. Hide's theorem states that in order for an atmosphere to super-rotate, non-axisymmetric disturbances (eddies) are required to induce transport of angular momentum up its local gradient. This raises a question as to the origin and nature of the disturbances that operate in super-rotating atmospheres to induce the required angular momentum transport.

The primary technique employed to investigate this question has involved numerically modelling super-rotating atmospheres, and diagnosing the processes that give rise to super-rotation in the simulations. These modelling efforts can be separated into one of two approaches. The first approach utilises 'realistic', tailor-made models of Solar System atmospheres where super-rotation is present (e.g., Venus and Titan) to investigate the specific processes responsible for generating super-rotation on each planet. The second approach takes simple, 'Earth-like' models, typically dry dynamical cores with radiative transfer represented using a Newtonian cooling approach, and explores the effect of varying a single (or occasionally multiple) planetary parameters (e.g., the planetary radius or rotation rate) on the atmospheric dynamics. Notably, studies of this flavour have shown that super-rotation may emerge 'spontaneously' on planets with slow rotation rate or small radius (relative to the Earth's; Venus and Titan have these characteristics). However, the strength of super-rotation obtained in simulations of this type is far weaker than that observed in Venus' or Titan's atmospheres, or in tailored numerical models of either planet.

In this work, our aim is to bridge the gap between these two modelling approaches. We will present results from a suite of simulations using an idealised general circulation model with a semi-grey representation of radiative transfer. Our experiments explore the effects of varying planetary size and rotation rate, atmospheric mass, and atmospheric absorption of shortwave radiation on the acceleration of super-rotation. A novel aspect of this work is that we vary multiple planetary properties away from their Earth-like 'defaults' in conjunction. This allows us to investigate how properties characteristic of the atmospheres of planets such as Venus and Titan combine to yield the strong super-rotation observed in their atmospheres (and realistic numerical models). We are also able to illustrate how features such as increased atmospheric mass and absorption of shortwave radiation modify the weakly super-rotating state obtained in simple, Earth-like models towards one more characteristic of Titan or Venus.

How to cite: Lewis, N. and Read, P.: Planetary and atmospheric properties leading to strong super-rotation in terrestrial atmospheres studied with a semi-grey GCM, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4855, https://doi.org/10.5194/egusphere-egu21-4855, 2021.

11:16–11:18
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EGU21-15410
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ECS
Fabian Wunderlich, Markus Scheucher, John Lee Grenfell, Franz Schreier, Clara Sousa-Silva, Mareike Godolt, and Heike Rauer

Rocky extrasolar planets orbiting M dwarfs are prime targets in the search for habitable surface conditions and biosignatures with near-future telescopes like the James Webb Space Telescope (JWST) and the Extremely Large Telescope (ELT). Even for the closest known targets the capabilities to characterize Earth-like or CO2-dominated atmospheres with JWST or ELT might still be limited to a few molecules such as CO2 or CH4. Hence it would be difficult to draw conclusions on the surface conditions and potential habitability of these planets. In clear H2-He atmospheres the molecular features in transmission spectra could be much larger and hence potential biosignatures might be detectable.

In this study, we investigate the detectability of the potential biosignatures NH3, PH3, CH3Cl, and N2O, assuming different H2-He atmospheres for the habitable zone super-Earth LHS 1140 b. Recent observations of the atmosphere of LHS 1140 b suggest that the planet might hold a clear H2-dominated atmosphere and might show an absorption feature around 1.4 µm due to H2O or CH4 absorption. Here we use the coupled convective-climate-photochemistry model 1D-TERRA to simulate H2 atmospheres of LHS 1140 b with different amounts of CH4 and assuming that the planet has an ocean and a biosphere.

The destruction of the potential biosignatures NH3, PH3, CH3Cl, and N2O shows a weak dependence on the concentrations of CH4. For weak abundances of CH4 only 5 to 10 transits are required to detect these molecules with JWST or ELT. However, for CH4 surface mixing ratios of a few percent only NH3 and N2O might be detectable with less than 10 transits. A scenario with large abundances of CH4 is consistent with the spectral feature at 1.4 µm and such an atmosphere might allow habitable surface temperatures. If this spectral feature at 1.4 µm originates from H2O absorption, the planet is likely not habitable at the surface.

How to cite: Wunderlich, F., Scheucher, M., Grenfell, J. L., Schreier, F., Sousa-Silva, C., Godolt, M., and Rauer, H.: Detectability of biosignatures on LHS 1140 b, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15410, https://doi.org/10.5194/egusphere-egu21-15410, 2021.

11:18–11:45