References of "Gkouvelis, Leonardos"
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See detailMAVEN‐IUVS observations of the CO2+ UV doublet and CO Cameron bands in the Martian thermosphere: Aeronomy, seasonal and latitudinal distribution.
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Ritter, Birgit ULiege et al

in Journal of Geophysical Research. Space Physics (2019)

We analyze two Martian years of dayglow measurements of the CO Cameron bands and the CO2+ ultraviolet doublet (UVD) at 298-299 nm with the Imaging UltraViolet Spectrograph on board the Maven orbiter. We ... [more ▼]

We analyze two Martian years of dayglow measurements of the CO Cameron bands and the CO2+ ultraviolet doublet (UVD) at 298-299 nm with the Imaging UltraViolet Spectrograph on board the Maven orbiter. We show that the altitude and the brightness of the two emissions peaks are strongly correlated, although data were collected over a wide range of latitudes and seasons. veraged limb profiles are presented and compared with numerical simulations based on updated calculations of the production of the CO (a3Π) and the CO2+ (B 2Σ) states. The model simulations use the solar flux directly measured on board MAVEN with the Extreme Ultraviolet Monitor (EUVM) and the neutral densities provided by the Mars Climate Database (MCD) version 5.3, adapted to the conditions of the observations. We show that the altitude and the shape of the sample limb profiles are well reproduced using the MCD neutral atmosphere. The simulated peak intensities of the CO2+ UVD and Cameron bands are in good agreement considering the uncertainties on the excitation cross sections and the calibration of the IUVS and EUVM instruments. No significant adjustment of the electron impact cross section on CO2 to produce the a3Π state is needed. Seasonal-latitudinal maps of the Cameron and UVD peak altitude observed during two Martian years show variations as large as 23 km. Model simulations of the amplitude of these changes are in fair agreement with the observations except during the southern summer dust period (Ls = 270°-320°) when the calculated rise of the dayglow layer is underestimated. [less ▲]

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See detailCharacteristics of Mars UV dayglow emissions from atomic oxygen at 130.4 and 135.6 nm: MAVEN/IUVS limb observations and modeling.
Ritter, Birgit ULiege; Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege et al

in Journal of Geophysical Research. Space Physics (2019)

We present an overview of two Martian years oxygen dayglow limb observations of the ultraviolet (UV) emissions at 130.4 nm and 135.6 nm. The data have been collected with the IUVS instrument on board the ... [more ▼]

We present an overview of two Martian years oxygen dayglow limb observations of the ultraviolet (UV) emissions at 130.4 nm and 135.6 nm. The data have been collected with the IUVS instrument on board the MAVEN spacecraft. We use solar flux measurements of EUVM on board MAVEN to remove the solar induced variation and show the variations of the maximum limb brightness and altitude with season, SZA and latitude, which reflects the strong variability of the Martian atmosphere. The 130.4 and 135.6 nm peak brightness and altitudes are strongly correlated and behave similarly. Both emissions are modeled for selected data using Monte Carlo codes to calculate emissions arising from electron impact on O and CO2. Additional radiative transfer calculations are made to analyze the optically thick 130.4 nm emission. Model atmospheres from the Mars Climate Database serve as input. Both simulated limb profiles are in good agreement with the observations despite some deviations. We furthermore show that the observed 130.4 nm brightness is dominated by resonance scattering of the solar multiplet with a contribution (15-20%) by electron impact on O. Over 95% of the excitation at 135.6 nm arises from electron impact on O. Simulations indicate that the limb brightness is dependent on the oxygen and CO2 content, while the peak emission altitude is mainly driven by the CO2 content because of absorption processes. We deduce [O]/[CO2] mixing ratios of 3.1% and 3.0% at 130 km for datasets collected at LS=350° in Martian years 32 and 33. [less ▲]

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See detailMartian dust storm impact on atmospheric H 2 O and D/H observed by ExoMars Trace Gas Orbiter
Vandaele, A. C.; Korablev, O.; Daerden, F. et al

in Nature (2019), 568

Global dust storms on Mars are rare 1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere 3 , primarily owing to ... [more ▼]

Global dust storms on Mars are rare 1,2 but can affect the Martian atmosphere for several months. They can cause changes in atmospheric dynamics and inflation of the atmosphere 3 , primarily owing to solar heating of the dust 3 . In turn, changes in atmospheric dynamics can affect the distribution of atmospheric water vapour, with potential implications for the atmospheric photochemistry and climate on Mars 4 . Recent observations of the water vapour abundance in the Martian atmosphere during dust storm conditions revealed a high-altitude increase in atmospheric water vapour that was more pronounced at high northern latitudes 5,6 , as well as a decrease in the water column at low latitudes 7,8 . Here we present concurrent, high-resolution measurements of dust, water and semiheavy water (HDO) at the onset of a global dust storm, obtained by the NOMAD and ACS instruments onboard the ExoMars Trace Gas Orbiter. We report the vertical distribution of the HDO/H 2 O ratio (D/H) from the planetary boundary layer up to an altitude of 80 kilometres. Our findings suggest that before the onset of the dust storm, HDO abundances were reduced to levels below detectability at altitudes above 40 kilometres. This decrease in HDO coincided with the presence of water-ice clouds. During the storm, an increase in the abundance of H 2 O and HDO was observed at altitudes between 40 and 80 kilometres. We propose that these increased abundances may be the result of warmer temperatures during the dust storm causing stronger atmospheric circulation and preventing ice cloud formation, which may confine water vapour to lower altitudes through gravitational fall and subsequent sublimation of ice crystals 3 . The observed changes in H 2 O and HDO abundance occurred within a few days during the development of the dust storm, suggesting a fast impact of dust storms on the Martian atmosphere. © 2019, The Author(s), under exclusive licence to Springer Nature Limited. [less ▲]

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See detailNo detection of methane on Mars from early ExoMars Trace Gas Orbiter observations
Korablev, O.; Vandaele, A. C.; Montmessin, F. et al

in Nature (2019), 568

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today 1 . A number of different measurements of methane show evidence of ... [more ▼]

The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today 1 . A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations 2–5 . These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere 6,7 , which—given methane’s lifetime of several centuries—predicts an even, well mixed distribution of methane 1,6,8 . Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections 2,4 . We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater 4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally. [less ▲]

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See detailThe O(1S) 297.2 nm dayglow emission: a tracer of CO2 density variations in the Martian lower thermosphere
Gkouvelis, Leonardos ULiege; Gérard, Jean-Claude ULiege; Ritter, Birgit ULiege et al

in Journal of Geophysical Research. Planets (2018), 123

The O(1S) metastable atoms can radiatively relax by emitting airglow at 557.7 and 297.2 nm. The latter one has been observed with the Imaging Ultraviolet Spectrograph onboard the Mars Atmosphere and ... [more ▼]

The O(1S) metastable atoms can radiatively relax by emitting airglow at 557.7 and 297.2 nm. The latter one has been observed with the Imaging Ultraviolet Spectrograph onboard the Mars Atmosphere and Volatile Evolution Mars orbiter since 2014. Limb profiles of the 297.2-nm dayglow have been collected near periapsis with a spatial resolution of 5 km or less. They show a double-peak structure that was previously predicted but never observed during earlier Mars missions. The production of both 297.2-nm layers is dominated by photodissociation of CO2. Their altitude and brightness is variable with season and latitude, reflecting changes in the total column of CO2 present in the lower thermosphere. Since the lower emission peak near 85 km is solely produced by photodissociation, its peak is an indicator of the unit optical depth pressure level and the overlying CO2 column density. Its intensity is directly controlled by the Lyman-α solar flux reaching the Martian upper atmosphere. We take advantage of the Lyman-α flux measurements of the solar Extreme Ultraviolet Monitor instrument onboard Mars Atmosphere and Volatile Evolution to model the observed OI 297.2-nm limb profiles. For this, we combine photodissociation sources with chemical processes and photoelectron impact excitation. To determine the relative importance of the excitation processes, we apply the model to the atmospheric structure measured by the Viking 1 lander before applying it to a model atmosphere. We find very good agreement with the lower peak structure and intensity if the CO2 density provided by the Mars Climate Database is scaled down by a factor between 0.50 and 0.66. We also determine that the previously uncertain quantum yield for production of O(1S) atoms by photodissociation of CO2 at Lyman-α wavelength is about 8%. [less ▲]

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See detailMars emissions from CO and CO2+: IUVS-MAVEN limb observations and model
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Ritter, Birgit ULiege et al

Poster (2018, September 17)

The IUVS Ultraviolet spectrograph (McClintock et al. 2014) on board MAVEN has been collecting thousands of airglow (Jain et al. 2015) or auroral (Schneider et al., 2015) limb profiles in the range 120 to ... [more ▼]

The IUVS Ultraviolet spectrograph (McClintock et al. 2014) on board MAVEN has been collecting thousands of airglow (Jain et al. 2015) or auroral (Schneider et al., 2015) limb profiles in the range 120 to 340 nm (Fig. 1) since November 2014. We have analyzed more that three years of airglow observations and compared them to model simulations. MAVEN has been quasi-continuously collecting airglow observations since November 2014, covering more than 1.5 Martian year and various latitudes ranges. The main features are emissions from CO, CO2+, O, N2 and C. In this work, we compare the characteristics of the CO2+ ultraviolet doublet (UVD) limb profiles with model simulations. From this comparison, we derive the CO2 column density above the 120-130 km region. [less ▲]

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See detailAtomic oxygen in the Martian thermosphere traced by the 130.4 and 135.6 nm emission lines with MAVEN/IUVS
Ritter, Birgit ULiege; Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege et al

Conference (2018, September)

We analyze limb observations of dayglow emissions from atomic oxygen in the upper Martian atmosphere. The data has been collected during the last almost four years by the Imaging Ultraviolet Spectrograph ... [more ▼]

We analyze limb observations of dayglow emissions from atomic oxygen in the upper Martian atmosphere. The data has been collected during the last almost four years by the Imaging Ultraviolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) spacecraft. Mean profiles for specific solar longitude, latitude and solar zenith angle ranges are created. We then use atmospheres from the Mars General Circulation models and in situ solar flux data from the MAVEN Extreme Ultraviolet Monitor (EUVM) to perform Monte Carlo and radiative transfer modeling for comparison with the observations. In order to match the results and to eventually retrieve oxygen densities, scaling factors are applied to the GCM atmospheric densities. We will present preliminary results of this analysis [less ▲]

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See detailComparison between IUVS-MAVEN limb dayglow observations and modelling
Gkouvelis, Leonardos ULiege; Gérard, Jean-Claude ULiege; Ritter, Birgit ULiege et al

Poster (2018, May)

Limb observations of airglow emissions is a standard technique to study the altitude profiles of the chemical elements in the Martian atmosphere and its thermal structure. Several previous missions have ... [more ▼]

Limb observations of airglow emissions is a standard technique to study the altitude profiles of the chemical elements in the Martian atmosphere and its thermal structure. Several previous missions have performed observations in the past (Mariners, Mars express). Recently the IUVS Ultraviolet spectrograph (McClintock et al. 2014) on board MAVEN has been collecting thousands of airglow (Jain et al. 2015) or auroral (Schneider et al., 2015) limb prof iles in the range 120 to 340 nm. We have analysed more than three years of airglow observations and compared them to model simulations. The objective is to study the CO2, O, CO and other density prof iles as well as thermospheric temperatures. [less ▲]

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See detailMetastable oxygen O(1S) Martian airglow: observations and model
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Ritter, Birgit ULiege et al

Conference (2018, May)

Limb profiles of OI 297.2 nm dayglow observed with IUVS/MAVEN show seasonal and latitudinal variations of the intensity and altitude of both peaks. The production of O(1S) atoms in the Martian upper ... [more ▼]

Limb profiles of OI 297.2 nm dayglow observed with IUVS/MAVEN show seasonal and latitudinal variations of the intensity and altitude of both peaks. The production of O(1S) atoms in the Martian upper atmosphere is dominated by photodissociation of CO2 at all altitudes below 200 km. The lower peak is produced by penetration of Ly-α solar radiation down to the 80 km region. The quantum yield for O(1S) production by CO2 dissociation by Lyman-α is about 10%. The 297.2 nm emission changing peak altitude reflects variations of the CO2 column density and thus the pressure level [less ▲]

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See detailMars UV-Visible airglow observations and predictions for EXOMARS-TGO
Gérard, Jean-Claude ULiege; Gkouvelis, Leonardos ULiege; Ritter, Birgit ULiege et al

Conference (2018, February)

Airglow observations have proven to be an efficient tool to probe composition and dynamics of planetary atmospheres. Several missions to Mars such as Mariners, Mars Express and MAVEN were equipped with ... [more ▼]

Airglow observations have proven to be an efficient tool to probe composition and dynamics of planetary atmospheres. Several missions to Mars such as Mariners, Mars Express and MAVEN were equipped with ultraviolet spectrometers that probed the distribution of airglow intensity features in the spectral range extending from 120 to 340 nm. They have provided a wealth of information on several emissions arising from O, C and N excited atoms or CO, CO2 + and N2 molecules. These, in turn, have been analyzed to provide thermospheric temperature, O densities, etc. [less ▲]

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See detailAurorae on Mars
Ritter, Birgit ULiege; Gérard, Jean-Claude ULiege; Hubert, Benoît ULiege et al

Conference (2018, February)

Three kinds of UV aurora have been detected on Mars: the discrete aurora [1], the diffuse aurora [2], and the proton aurora [3]. The discrete and the diffuse aurora are seen on the Martian nightside and ... [more ▼]

Three kinds of UV aurora have been detected on Mars: the discrete aurora [1], the diffuse aurora [2], and the proton aurora [3]. The discrete and the diffuse aurora are seen on the Martian nightside and result from electron impact on the upper atmosphere. Figure 1 shows an electron excited auroral spectrum extended into the visible using laboratory measurements. The proton aurora is observed on the dayside and originates from precipitating protons. We present an overview of these aurorae, combining observations of the SPICAM ultraviolet spectrometer on board Mars Express and modeling results, giving an estimate of what we might be able to observe in the future with UVIS-NOMAD [4] on board Trace Gas Orbiter (TGO). [less ▲]

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See detailThe Mars atomic oxygen dayglow: predictions based on the OI 297.2 nm MAVEN/IUVS observations
Gkouvelis, Leonardos ULiege; Gérard, Jean-Claude ULiege; Hubert, Benoît ULiege

Conference (2017, June 23)

The oxygen green line at 557.7 nm corresponds to the 1S →1D forbidden transition of the O atom. It shares the same upper level as the 1S→ 3P UV line at 297.2 nm. The green line is a major component of the ... [more ▼]

The oxygen green line at 557.7 nm corresponds to the 1S →1D forbidden transition of the O atom. It shares the same upper level as the 1S→ 3P UV line at 297.2 nm. The green line is a major component of the visible terrestrial dayglow spectrum and accounts for the dominant color of the high-latitude auroral display. The 297.2 nm emission was first detected with spectrometers on board the Mariner missions. It has since has been observed at the limb in the Martian dayglow with the SPICAM (Mars Express) and IUVS (MAVEN) spectrographs. The sources of the 1S excitation in the Mars dayglow are electron impact on O, photodissociation and electron impact dissociation of CO2 and CO and dissociative recombination of O2+ ions. [less ▲]

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