Variability of the hydrogen in the martian upper atmosphere as simulated by a 3D atmosphere–exosphere coupling

Chaufray, Jean‐Yves; González‐Galindo, Francisco; Forget, F.; López‐Valverde, M. A.; Leblanc, François; Modolo, Ronan; Hess, S.

doi:10.1016/j.icarus.2014.08.038

Cited by 86 publications

(91 citation statements)

References 89 publications

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“…Additionally, daily irradiances in the 121–122 nm wavelength range measured by MAVEN EUVM clearly display a long‐term trend with increasing intensity when the Sun‐Mars distance decreases (Figure ), thus suggesting an increase in the photoionization frequency of the exospheric H atoms. As stated above, the upper H exosphere is mainly controlled by the averaged temperature at the exobase, which is UV dependent [ Chaufray et al , ]. Temporal variabilities in the simulated H densities (Figure ) partly arise as a result of the Martian thermospheric response to changes in the UV flux associated with variations in the heliocentric distance.…”

Section: Discussionmentioning

confidence: 93%

“…For the purpose of the present study, however, estimations of the exospheric H densities at altitudes higher than MAVEN spatial coverage during the time interval under study are needed. Therefore, H densities obtained in this study are derived using a 3‐D exospheric model detailed in Chaufray et al [, ], taking into account the nonuniform spatial distribution of H densities and temperatures at the exobase given by the 3‐D Laboratoire de Météorologie Dynamique Global Climate Model (LMD‐GCM) model [ González‐Galindo et al , ; Chaufray et al , ]. The LMD‐GCM describes the hydrogen cycle from the water photodissociation in the lower atmosphere to the escape at the exobase assuming Jeans escape only [ Chaufray et al , ].…”

Section: Description Of Maven Instruments and Adopted Numerical Simulmentioning

confidence: 99%

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Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

et al. 2016

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Measurements provided by the Magnetometer and the Extreme Ultraviolet Monitor (EUVM) on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft together with atomic H exospheric densities derived from numerical simulations are studied for the time interval from October 2014 up to March 2016. We determine the proton cyclotron waves (PCWs) occurrence rate observed upstream from Mars at different times. We also study the relationship with temporal variabilities of the high‐altitude Martian hydrogen exosphere and the solar EUV flux reaching the Martian environment. We find that the abundance of PCWs is higher when Mars is close to perihelion and decreases to lower and approximately constant values after the Martian Northern Spring Equinox. We also conclude that these variabilities cannot be associated with biases in MAVEN's spatial coverage or changes in the background magnetic field orientation. Higher H exospheric densities on the Martian dayside are also found when Mars is closer to perihelion, as a result of changes in the thermospheric response to variability in the ultraviolet flux reaching Mars at different orbital distances. A consistent behavior is also observed in the analyzed daily irradiances measured by the MAVEN EUVM. The latter trends point toward an increase in the planetary proton densities upstream from the Martian bow shock near perihelion. These results then suggest a method to indirectly monitor the variability of the H exosphere up to very high altitudes during large time intervals (compared to direct measurements of neutral particles), based on the observed abundance of PCWs.

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Section: Discussionmentioning

confidence: 93%

Section: Description Of Maven Instruments and Adopted Numerical Simulmentioning

confidence: 99%

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

et al. 2016

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“…The H escape flux calculated by Chaufray et al () varies by roughly a factor of 1,000 over the exobase. There is a maximum in the early morning and near the polar regions where temperatures are rising but the H bulge has not yet dissipated.…”

Section: Introductionmentioning

confidence: 89%

“…The interplay of these processes on Mars has been studied by Chaufray et al (, ), who extended the Laboratoire Météorologie Dynamique General Circulation Model (LMD‐GCM; Forget et al, ; Gonzalez‐Galindo et al, ) to include atomic and molecular hydrogen, the associated chemistry, vertical diffusion, and Jeans escape. The simulations encompassed the entire atmosphere, from the surface to the exobase, and were extended into the exosphere using Liouville's equation.…”

Section: Introductionmentioning

confidence: 99%

“…The simulations encompassed the entire atmosphere, from the surface to the exobase, and were extended into the exosphere using Liouville's equation. Chaufray et al () found that the H density near the exobase varied by a factor of several hundred with a density maximum near midnight during solstices and near dawn during equinox, due to circulation patterns in the thermosphere. The H escape rate in these simulations varied by a factor of ~8 due to seasonal effects with a maximum near northern winter solstice and a factor of ~5 due to solar cycle effects.…”

Section: Introductionmentioning

confidence: 99%

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Effect of the Lateral Exospheric Transport on the Horizontal Hydrogen Distribution Near the Exobase of Mars

et al. 2018

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We simulate the hydrogen density near the exobase of Mars, using the 3‐D Martian Global Circulation Model of Laboratoire de Météorologie Dynamique, coupled to an exospheric ballistic model to compute the downward ballistic flux. The simulated hydrogen distribution near the exobase obtained at two different seasons—Ls = 180° and Ls = 270°—is close to Zero Net Ballistic Flux equilibrium. In other words, the hydrogen density near the exobase adjusts to have a balance between the local upward ballistic and the downward ballistic flux due to a short lateral migration time in the exosphere compared to the vertical diffusion time. This equilibrium leads to a hydrogen density n near the exobase directly controlled by the exospheric temperature T by the relation nT5/2 = constant. This relation could be used to extend 1‐D hydrogen exospheric model of Mars used to derive the hydrogen density and escape flux at Mars from Lyman‐α observations to 3‐D model based on observed or modeled exospheric temperature near the exobase, without increasing the number of free parameters.

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Long-term variability of CO₂and O in the Mars upper atmosphere from MRO radio science data

Genova

Goossens

Lemoine

et al. 2015

J. Geophys. Res. Planets

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We estimate the annual variability of CO 2 and O partial density using approximately 6 years of Mars Reconnaissance Orbiter (MRO) radio science data from August 2006 to January 2012, which cover three full Martian years (from the northern hemisphere summer of 28 to the northern hemisphere summer of 31). These two elements are the dominant species at the MRO periapsis altitude, constituting about 70-80% of the total density. We report the recovered annual cycle of CO 2 and the annual and seasonal cycle of O in the upper atmosphere. Although no other observations are available at those altitudes, our results are in good agreement with the density measurements of the Mars Express Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars, which uses stellar occultations between 60 and 130 km to determine the CO 2 variability, and with the Mars Global Reference Atmospheric Model 2010 for the O annual and seasonal variabilities. Furthermore, the updated model provides more reasonable MRO drag coefficients (C D ), which are estimated to absorb mismodeling in the atmospheric density prediction. The higher content of dust in the atmosphere due to dust storms increases the density, so the C D s should compensate for this effect. The correlation between the drag coefficient and the dust optical depth, measured by the Mars Odyssey Thermal Emission Imaging System (THEMIS) instrument, increases from 0.4 to 0.8 with the a priori and adjusted models, respectively. The trend of C D s not only confirms a substantial improvement in the prediction of the atmospheric density with the updated model but also provides useful information for local dust storms, near MRO periapsis, that cannot be measured by the opacity level since THEMIS does not always sample the southern hemisphere evenly.

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Variability of the hydrogen in the martian upper atmosphere as simulated by a 3D atmosphere–exosphere coupling

Cited by 86 publications

References 89 publications

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

Effect of the Lateral Exospheric Transport on the Horizontal Hydrogen Distribution Near the Exobase of Mars

Long-term variability of CO₂and O in the Mars upper atmosphere from MRO radio science data

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Variability of the hydrogen in the martian upper atmosphere as simulated by a 3D atmosphere–exosphere coupling

Cited by 86 publications

References 89 publications

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

Proton cyclotron waves occurrence rate upstream from Mars observed by MAVEN: Associated variability of the Martian upper atmosphere

Effect of the Lateral Exospheric Transport on the Horizontal Hydrogen Distribution Near the Exobase of Mars

Long-term variability of CO2and O in the Mars upper atmosphere from MRO radio science data

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Product

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Long-term variability of CO₂and O in the Mars upper atmosphere from MRO radio science data