The upper atmosphere of Venus is still nowadays a highly unknown region in the scientific context of the terrestrial planetary atmospheres. The Earth’s stratosphere and mesosphere continue being studied with increasingly sophisticated sounders and in-situ instrumentation [1, 2]. Also on Mars, its intensive on-going exploration is gathering a whole new set of data on its upper atmosphere [3, 4, 5]. On Venus, however, the only recent progress came from theoretical model developments, from ground observations and from revisits of past missions’ data, like Pioneer Venus. More and new data are needed [6, 7, 8]. The arrival of the European Venus Express (VEX) mission at Venus on April 2006 marked the start of an exciting period with new data from a systematic sounding of the Venus atmosphere from orbit [9, 10]. A suite of diverse instrumentation is obtaining new observations of the atmosphere of Venus. After one and a half years in orbit, and although the data are still under validation and extensive analysis, first results are starting to be published. In addition to those global descriptions of VEX and its first achievements, we present here a review on what VEX data are adding to the exploration of this upper region of the atmosphere of Venus. We present measurements at those altitudes from one of the infrared sounders aboard VEX, the instrument VIRTIS, as an example of unique insights on the upper mesosphere and lower thermosphere of Venus, and discuss briefly the synergy with other instruments on VEX. We will conclude with our opinion on the importance and limitations of the Venus Express mission in order to broaden our global understanding of the upper layers of the terrestrial atmospheres.
<p><strong>Abstract</strong></p> <p>The D/H ratio measured in the Martian atmosphere gives an estimation of the planet&#8217;s water escape rate. We present here a global circulation model including the water isotope HDO and the main physical processes of fractionation. Modeling the D/H cycle accompanies the recent measurements from the ACS spectrometer onboard the orbiter TGO. The comparison between the model outputs and the TGO/ACS observations reveal some discrepancies, in particular during the second half of the martian year, when the escape is supposed to be the most efficient. The present work aims at studying these main differences.</p> <p><strong>Introduction</strong></p> <p>The high value of the Martian D/H ratio, derived from the HDO/H<sub>2</sub>O abundance ratio, in comparison to that of the Earth&#8217;s oceans[1],[2],[3],[4], is an indicator of the large escape of water from Mars over time. Apart from the mass difference between both isotopes, the differential escape of H and D comes from the preferential photolysis of H<sub>2</sub>O over HDO[5] and the preferential condensation of HDO over H<sub>2</sub>O [6],[7],[8]. The NOMAD and ACS instruments onboard ExoMars Trace Gas Orbiter (TGO) have recently provided unprecedented observations of vertical variations in HDO abundance and D/H ratio in the martian atmosphere [9],[10],[11],[12], motivating model development [13],[14]. In particular, TGO data cover the second half (&#8220;dusty season&#8221;) of martian year (MY) 34, which includes a Global Dust Storm (GDS) (Ls 180&#176;-230&#176;) and a regional dust storm (Ls 315&#176;-330&#176;). These dust events have been proven to be of particular importance in the hydrogen escape inventory [12],[15],[16],[17],[18].</p> <p><strong>HDO modeling</strong></p> <p>The D/H ratio measured in the Martian atmosphere gives an estimation of the planet&#8217;s water escape rate. We present here a global circulation model including the water isotope HDO and the main physical processes of fractionation. Modeling the D/H cycle accompanies the recent measurements from the ACS spectrometer onboard the orbiter TGO. The comparison between the model outputs and the TGO/ACS observations reveal some discrepancies, in particular during the second half of the martian year, when the escape is supposed to be the most efficient. The present work aims at studying these main differences. Based on Montmessin et al. 2005[19], Rossi et al. 2021[13] have introduced the HDO cycle in the Mars Planetary Climate Model (Mars PCM), formely known as the LMD Mars Global Climate Model[20]. Vals et al. 2022[21] have recently adapted these implementations to the complete representation of the water ice clouds, including the radiative effect of clouds[22] and microphysics, the latter allowing the modeling of supersaturation[23]. The effect of kinetics in the fractionation by condensation has also been included, as has the photodissociation of HDO and the photochemical reactions of the deuterated species [24],[25],[26]. Rossi et al. 2022[27] have used the improved model to compare with TGO/ACS/MIR retrievals of D/H profiles[28] and revealed some discrepancies, which account for the challenge of reproducing the D/H cycle, depending on key components of the Martian atmosphere such as the water and dust cycles.</p> <p><strong>Preliminary results</strong></p> <p>By comparing the simulations and the observations, we particularly notice an overestimation by the model of water vapor above &#8764;60 km occuring near the GDS in MY34, and an underestimation near perihelion in the southern hemisphere (see Figure 1). The difference in water vapor vertical distribution has a direct impact on the D/H profiles (see Figures 2 and 3). In this work, we want to analyse these differences to eventually propose some model improvements. Further comparisons and results for MY34 and 35 will be shown at the conference.</p> <p><img src="" alt="" width="1103" height="735" /></p> <p>Figure 1: Water vapor volume mixing ratio in ppmv as measured by TGO/ACS/NIR[16] (black) and as computed by the model (red) at different altitude ranges.</p> <p><img src="" alt="" /></p> <p>Figure 2: Water vapor volume mixing ratio, temperature and saturation as measured by TGO/ACS/NIR[16], and D/H profiles as measured by TGO/ACS/MIR[28] (black) and as computed by the model (red) during MY34 between solar longitudes 235&#176;, 245&#176; and latitudes -25&#176;N, 25&#176;N.</p> <p><img src="" alt="" /></p> <p>Figure 3: Same layout as Figure 2 between solar longitudes 270&#176;, 300&#176; and latitudes -60&#176;N, 45&#176; N.</p> <p><strong>References</strong></p> <p>[1] Owen et al.: Science, 240 (4860), 1767-1770, 1988</p> <p>[2] Encrenaz et al.: A&A, 612 , A112, 2018.</p> <p>[3] Krasnopolsky: Icarus, 257 , 377 - 386, 2015</p> <p>[4] Villanueva et al.: Science, 348 (6231), 218&#8211;221, 2015.</p> <p>[5] Cheng et al.: Geophysical Research Letters, 26 (24), 3657-3660, 1999</p> <p>[6] Krasnopolsky: Icarus, (2), 597-602, 2000.</p> <p>[7] Fouchet et al.: Icarus, 144 , 114-123, 2000.</p> <p>[8] Bertaux et al.: Journal of Geophysical Research: Planets, 106 (E12), 32879-32884, 2001.</p> <p>[9] Vandaele et al.: Space Science Reviews, 214 (5), 80, 2018.</p> <p>[10] Vandaele et al.: Nature, 568 (7753), 521-525, 2019.</p> <p>[11] Korablev et al.: Space Science Reviews, 214 , 7, 2018.</p> <p>[12] Korablev et al.: Nature, 568 (7753),517-520, 2019.</p> <p>[13] Rossi et al.: grl , 48 (7), e90962, 2021.</p> <p>[14] Daerden et al.: Journal of Geophysical Research (Planets), 127 (2), e07079, 2022.</p> <p>[15] Aoki et al.: Journal of Geophysical Research (Planets), 124 (12), 3482-3497, 2019.</p> <p>[16] Fedorova et al.: Science, 367 (6475), 297-300, 2020.</p> <p>[17] Neary et al.: Geophysical Research Letters, 47 (7), e84354, 2020.</p> <p>[18] Chaffin et al.: Nature Astronomy, 5 , 1036-1042, 2021.</p> <p>[19] Montmessin et al.: Journal of Geophysical Research, 2005.</p> <p>[20] Forget et al.: JGR, 104:24,155&#8211;24,176, 1999.</p> <p>[21] Vals et al.: Journal of Geophysical Research (Planets), under revision, 2022.</p> <p>[22] Madeleine et al. : Geophys. Res. Lett., 39 , 23202, 2012.</p> <p>[23] Navarro et al.: Journal of Geophysical Research (Planets), 2014.</p> <p>[24] Lef&#232;vre et al.: Journal of Geophysical Research (Planets), 126 (4), 2021.</p> <p>[25] Cheng et al.: Journal of Chemical Physics, 120 (1), 224-229, 2004.</p> <p>[26] Chung et al.: Nuclear Instruments and Methods in Physics Research A, 467 (2002), 1572-1576, 2001.</p> <p>[27] Rossi et al.: Journal of Geophysical Research (Planets), under revision, 2022.</p> <p>[28] Alday et al.: Nature Astronomy, 5, 943-950, 2021.</p>
Abstract We report results from a study of two consecutive Martian years of imaging observations of nitric oxide ultraviolet nightglow by the Imaging Ultraviolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution (MAVEN) mission spacecraft. The emission arises from recombination of N and O atoms in Mars' nightside mesosphere. The brightness traces the reaction rate as opposed to the abundance of constituents, revealing where circulation patterns concentrate N and O and enhance recombination. Emissions are brightest around the winter poles, with equatorial regions brightening around the equinoxes. These changes offer clear evidence of circulation patterns transitioning from a single cross‐equatorial cell operating during solstice periods to more symmetric equator‐to‐poles circulation around the equinoxes. Prominent atmospheric tides intensify the emissions at different longitudes, latitude ranges, and seasons. We find a strong eastward‐propagating diurnal tide (DE2) near the equator during the equinoxes, with a remarkably bright spot narrowly confined near (0°, 0°). Wave features at the opposite winter poles are dissimilar, reflecting different circulation patterns at perihelion versus aphelion. LMD‐MGCM simulations agree with the patterns of most observed phenomena, confirming that the model captures the dominant physical processes. At the south winter pole, however, the model fails to match a strong wave‐1 spiral feature. Observed brightnesses exceed model predictions by a factor of 1.9 globally, probably due to an underestimation of the dayside production of N and O atoms. Further study of discrepancies between the model and observations offers opportunities to improve our understanding of chemical and transport processes controlling the emission.
Abstract. Global distributions of the CO2 vmr (volume mixing ratio) in the mesosphere and lower thermosphere (from 70 km up to 142 km) have been derived from high resolution mid-IR spectra. This is the first time that the CO2 vmr has been retrieved in the 120–140 km range. The CO2 vmrs have been retrieved using MIPAS daytime limb emission spectra from the 4.3 µm region in its upper atmosphere (UA) mode (data version v5r_CO2_622). The dataset spans from January 2005 until March 2012. The retrieval of CO2 has been performed jointly with the line of sight (LOS) by using a non-local thermodynamic equilibrium (non-LTE) retrieval scheme. The non-LTE model incorporates the accurate vibrational-vibrational and vibrational-translational collisional rates recently derived from the MIPAS spectra. It also takes advantage of simultaneous MIPAS measurements of other atmospheric parameters, as the kinetic temperature (up to ~100 km) from the CO2 15 µm region, the thermospheric temperature from the NO 5.3 µm emission, and the O3 measurements (up to ~100 km). The latter is very important for the calculations of the non-LTE populations because it strongly constrains the O(1D) concentration below ~100 km. The estimated precision of the retrieved CO2 vmr profiles varies with altitude ranging from ~1 % below 90 km, to 5% around 120 km and larger than 10 % above 130 km. There are some latitudinal and seasonal variations of the precision, which are mainly driven by the solar illumination conditions. The retrieved CO2 profiles have a vertical resolution of about 5–7 km below 120 km and between 10 and 20 km at 120–142 km. We have shown that the inclusion of the LOS as joint fit parameter improves the retrieval of CO2, allowing a clear discrimination between the information of CO2 concentration and the LOS and also leading to significantly smaller systematic errors. The retrieved CO2 has a much better accuracy than previous limb emission measurements, because of the highly accurate rate coefficients recently derived from MIPAS, and the simultaneous MIPAS measurements of other key atmospheric parameters needed for the non-LTE modeling like the kinetic temperature and the O3 concentration. The major systematic error source is the uncertainty of the pressure/temperature profiles, inducing errors of up to 15 % above 100 km, and of ~5% around 80 km at mid-latitude conditions. The errors due to uncertainties in the O(1D) and O(3P) profiles are within 3–4 % in the 100–120 km region, and those due to uncertainties in the gain calibration and in the near-IR solar flux are within ~2 % at all altitudes. The retrieved CO2 shows the major features expected and predicted by general circulation models. In particular, its abrupt decline above 80–90 km and the seasonal change of the latitudinal distribution, with higher CO2 abundances in polar summer from 70 km up to ~95 km and lower CO2 vmr in the polar winter. Above ~95 km, CO2 is more abundant in the polar winter than at mid-latitudes and polar summer regions, caused by the reversal of the mean circulation in that altitude region. Also, the solstice seasonal distribution, with a significant pole-to-pole CO2 gradient, lasts about 2.5 months in each hemisphere, while the seasonal transition occurs quickly.
The recently discovered super-Earth LP 890-9 c is an intriguing target for atmospheric studies as it transits a nearby, low-activity late-type M-dwarf star at the inner edge of the Habitable Zone. Its position at the runaway greenhouse limit makes it a natural laboratory to study the climate evolution of hot rocky planets. We present the first 3D-GCM exo-Venus model for a modern Venus-like atmosphere (92 bar surface pressure, realistic composition, H$_2$SO$_4$ radiatively-active clouds), applied to the tidally-locked LP 890-9c to inform observations by JWST and future instruments. If LP 890-9 c has developed into a modern exo-Venus, then the modelled temperatures suggest that H$_2$SO$_4$ clouds are possible even in the substellar region. Like on modern Venus, clouds on LP 890-9 c would create a flat spectrum. The strongest CO$_2$ bands in transmission predicted by our model for LP 890-9 c are about 10 ppm, challenging detection, given JWST estimated noise floor. Estimated phase curve amplitudes are 0.9 and 2.4 ppm for continuum and CO$_2$ bands, respectively. While pointing out the challenge to characterise modern exo-Venus analogues, these results provide new insights for JWST proposals and highlight the influence of clouds in the spectrum of hot rocky exoplanet spectra.
Abstract We study the seasonal and geographical variability of the peak electron density and the altitude of the main ionospheric peak at Mars. For this purpose, we use the data obtained by the ESA Mars Express mission, namely by the radar MARSIS and the radio occultation experiment MaRS. The accumulation of data during the long lifetime of Mars Express provides for the first time an almost complete seasonal and geographical coverage. We first remove the dominant variability factors affecting the main ionospheric peak, namely the effect of changes in the solar zenith angle (SZA), and the changes in the solar ultraviolet radiation output at the Sun. When averaging results obtained at all latitudes, we find that the seasonal variation of both the peak density and the peak altitude can be well reproduced by sinusoidal functions with amplitudes about 8%–9% of the annually averaged peak density, and between 8 and 9.5 km for the peak altitude. We also find elevated peak electron densities in the region of strong crustal fields and latitudinal asymmetries in both the peak density and altitude. Comparing the seasonal evolution of the peak altitude during Mars Year 28, a year with a global dust storm, and the rest of the years, we find that the global dust storm raised the altitude of the ionospheric peak by about 10–15 km.
Abstract During Mars dust storms, atmospheric heating and expansion moves the ionospheric peak upward. Typically, peak altitude increases by no more than 10 km, and this increase occurs simultaneously with the expansion of the dust storm. However, Felici et al. (2020), https://doi.org/10.1029/2019JA027083 , using the Mars Atmosphere Volatile EvolutioN (MAVEN) Radio Occultation Science Experiment (ROSE), reported an unusually large increase of ∼20 km at southern latitudes in early October 2016 during a modest dust storm. Here, we investigate why the ionospheric peak altitude increased so much in these observations. We extend the time series of ionospheric peak altitude values beyond the limited extent of the ROSE observations by applying a one‐dimensional photochemical model, in which neutral atmospheric conditions are based on in situ MAVEN Neutral Gas Ion Mass Spectrometer observations at similar latitudes and solar zenith angles to those observed by ROSE. We find that the ionospheric peak altitude was highest throughout October 2016 yet both the local and global atmospheric dust loading were greatest 1 month earlier. We hypothesize that (a) a portion of the unusually large 20 km enhancement in peak altitude and (b) the unusual delay between the greatest dust loading and the highest peak altitude were both associated with the occurrence of perihelion, which maximizes solar heating of the atmosphere, in late October 2016.
General introductionThe Mars Climate Database (MCD) is a database of meteorological fields derived from General Circulation Model (GCM) numerical simulations of the Martian atmosphere using the Mars Planetary Climate Model (PCM) and validated using available observational data. The MCD includes complementary post-processing schemes such as high spatial resolution interpolation of environmental data and means of reconstructing the variability thereof [1].The latest version of the MCD, version 6.1, was released in December 2022. The Mars PCM (formerly known as the LMD GCM) that is used to create the MCD data is developed at Laboratoire de Météorologie Dynamique du CNRS (Paris, France) [2] in collaboration with LATMOS (Paris, France), the Open University (UK), the Oxford University (UK) and the Instituto de Astrofisica de Andalucia (Spain) with support from the European Space Agency (ESA) and the Centre National d'Etudes Spatiales (CNES). The MCD is intended to be useful and used in the framework of engineering applications as well as in the context of scientific studies which require accurate knowledge of the state of the Martian atmosphere. Over the years, various versions of the MCD have been released and handed to more than 400 teams around the world. It is cited in more than 600 peer-reviewed publications (source: NASA ADS). The MCD is freely available upon request via an online form on the dedicated website: http://www-mars.lmd.jussieu.fr which moreover includes a convenient web interface for quick looks. Overview of the Mars Climate Database contentsThe MCD provides mean values and statistics of the main meteorological variables (atmospheric temperature, density, pressure and winds) as well as atmospheric composition (including dust and water vapor and ice content), as the GCM from which the datasets are obtained includes water cycle, chemistry, and ionosphere models[2]. The database extends up to and including the thermosphere (~350km). Since the influence of Extreme Ultra Violet (EUV) input from the sun is significant in the latter, 3 EUV scenarios (solar minimum, average and maximum inputs) account for the impact of the various states of the solar cycle. As the main driver of the Martian climate is the dust loading of the atmosphere [3-4], the MCD provides climatologies over a series of synthetic dust scenarios: standard year (a.k.a. climatology), cold (i.e: low dust), warm (i.e: dusty atmosphere) and dust storm (see Figure 2 for an illustrative example), These are derived from home-made, instrument-derived (TES, THEMIS, MCS, MERs), dust climatology of the last 12 Martian years [5]. In addition, we also provide additional “add-on” scenarios which focus on individual Martian Years (from MY 24 to MY 35) for users more interested in more specific climatologies than the MCD baseline scenarios.MCD outputs and validationThe MCD in intended to be useful for both engineering and scientific studies. Known applications include entry descent and landing (EDL) studies for Mars missions, investigations of some specific Martian issues (via coupling of the MCD with homemade codes), analysis of observations (Earth-based as well as with various instruments onboard Mars Express, Mars Reconnaissance Orbiter, Trace Gas Orbiter, Emirates Mars Mission),… In practice the MCD provides users with:- Mean values and statistics of main meteorological variables (atmospheric temperature, density, pressure and winds), as well as surface pressure and temperature, CO2 ice cover, thermal and solar radiative fluxes, dust column opacity and mixing ratio, [H20] vapor and ice concentrations, along with concentrations of many species: [CO], [O2], [O], [N2], [Ar], [H2], [O3], [H] ..., as well as electrons mixing ratios. Column densities of these species are also given.- Physical processes in the Planetary Boundary Layer (PBL), such as PBL height, minimum and maximum vertical convective winds in the PBL, surface wind stress and sensible heat flux.- The possibility to reconstruct realistic conditions by combining the provided climatology with additional large scale (derived from Empirical Orthogonal Functions extracted from the GCM runs) and small scale perturbations (gravity waves).- Dust mass mixing ratio, along with estimated dust effective radius and dust deposition rate on the surface are provided.- A high resolution mode which combines high resolution (32 pixel/degree) MOLA topography records and Insight pressure records with raw lower resolution GCM results to yield, within the restriction of the procedure, high resolution values of atmospheric variables (pressure, but also temperature and winds via dedicated schemes). MCD version 6.1 has been validated using many available datasets, and these comparisons are detailed in the validation document [6] distributed with the software. References[1] Bierjon A. et al. (2023) International Planetary Probe Workshop 2023.[2] Forget F. et al. (2022) 7th Mars Atmosphere Modeling and Observation.[3] Bierjon A. et al. (2022) 7th Mars Atmosphere Modeling and Observation.[4] Pierron T. et al. (2022) 7th Mars Atmosphere Modeling and Observation.[5] Montabone L. et al. (2024) EuroPlanet Science Congress.[6] Forget F. et al. (2022) Mars Climate Database V6.1 Validation Document
