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Ultraviolet spectral imaging has been a powerful tool to investigate the cloud top of Venus, allowing for measurement of several minor gases (especially SO 2 , SO, O 3), of cloud top aerosol's microphysical properties and of atmospheric dynamics through tracking of the unevenly distributed UV absorber. After a brief review of recent UV instruments that orbited around Venus, we present the results of a state-of-the-art radiative transfer model from Marcq et al. (2020) to derive the spectral resolution and Signal-to-Noise ratio (SNR) required to derive abundances of these gases, retrieve optical properties of the aerosols beyond our current knowledge. This leads us to propose a two-channel UV hyperspectral push-broom imager called VeSUV (standing for Venusian Spectroscopy in UV) whose technical characteristics will improve on existing measurements by a factor of at least 2, and which is well suited to the integration into the payload of future low Venus orbit platforms such as the proposed EnVision mission to ESA M5 call. [ABSTRACT FROM AUTHOR]

The loss of water from Mars to space is thought to result from the transport of water to the upper atmosphere, where it is dissociated to hydrogen and escapes the planet. Recent observations have suggested large, rapid seasonal intrusions of water into the upper atmosphere, boosting the hydrogen abundance. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution by altitude. Water profiles during the 2018–2019 southern spring and summer stormy seasons show that high-altitude water is preferentially supplied close to perihelion, and supersaturation occurs even when clouds are present. This implies that the potential for water to escape from Mars is higher than previously thought. [ABSTRACT FROM AUTHOR]

The study of atmospheric emissions from orbit to probe the middle and upper atmosphere of Mars, which started with the Mariner missions, is living a golden era thanks to the European Space Agency (ESA) Mars Express mission and other subsequent missions built upon its success, including the ESA ExoMars Trace Gas Orbiter (TGO) mission. Here we summarize the most relevant information obtained by the analysis of atmospheric emissions data from Mars Express and TGO, about the temperature and density structure, the atmospheric dynamics, the chemistry and the atmospheric escape to space. Mars Express also opened a new field of research on Mars with the discovery of aurorae on the planet. We present here the most outstanding results collected by Mars Express about aurorae. Finally, we also discuss how later measurements by other missions have complemented Mars Express and TGO results, and the potential future developments relevant to this field of research. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Suite (ACS) on board ESA-Roscosmos ExoMars 2016 TraceGas Orbiter (TGO) spacecraft will complete one year of Mars observations in March 2019.ACS consists of three infrared spectrometers targeting the detection of trace gases of potentialgeophysical or biological interest, as well as the monitoring of the martian atmosphere state.ACS channels feature high resolving power (>10,000) and broad spectral coverage (0.7 to17 μm). The near-infrared (NIR) channel covers the 0.7-1.6 μm spectral rangewith a resolving power of ≥20,000. Results of solar occultation sounding by NIR,including profiling of H2O with high accuracy and in a broad altitude range, and thefirst ever profiling molecular oxygen O2 in the lower atmosphere will be reported.The mid-infrared (MIR) channel is a high spectral resolution (resolving power of≥30,000) instrument dedicated to solar occultation measurements in the 2.2-4.4 μmrange. MIR is conceived to accomplish the most sensitive measurements of the tracegases in the Martian atmosphere, allowing also parallel profiling of the abundantcomponents such as CO2, H2O and their isotopologues. MIR results putting stringentupper limits to methane abundance will be reported. The thermal-infrared channel(TIRVIM) is a Fourier-transform spectrometer with cryogenically-cooled detectorencompassing the spectral range of 1.7-17 μm. Observing the CO2 15-μm band in nadirTIRVIM returns temperature profiles from the surface up to 50-60 km, together withthe dust and water ice optical depth. Also the surface temperature is measured.In solar occultation TIRVIM delivers profiles of CO2, CO, H2O and aerosols, aswell allowing to distinguish between mineral and condensate aerosols. ACS hasmonitored the state of the martian atmosphere before and during the dust event2018A. The status of the experiment and key findings will be summarized in the talk. [ABSTRACT FROM AUTHOR]

The Trace Gas Orbiter (TGO) of the ESA-Roscosmos ExoMars mission has ended its trip to Mars, reaching the planet in October 2016. After a year-long aerobraking phase, its scientific mission has begun on April 22nd, 2018 with the execution of the first solar occultation. The primary objective of TGO is to detect, map and locate trace gas sources, possibly revealing a residual geophysical (or even biological) activity on Mars. The instrument of interest here is the infrared spectrometer Atmospheric Chemistry Suite (ACS). ACS covers a wavelength range from 0.7 to 17 μm at very high spectral resolution (λ / Δλ from 5,000 to 50,000). ACS operates in nadir and solar occultation. Its performance and scientific objectives make it complementary to NOMAD, the other spectrometer dedicated to trace gas characterization.A large part of the first months of the ACS observing mission has enabled the sensitive search of gaseous methane over a substantial fraction of the Martian globe. The results from the first occultation up until early September 2018 will be presented. This period incidentally covered the onset, the full development and the demise of the Planetary Encircling Dust Event observed by several other instruments orbiting currently around Mars. Observed conditions proved more favorable than anticipated, and it was possible in a few cases to probe the Martian atmosphere close to the surface (<5 km) where the MSL Curiosity rover has established the existence of a seasonally varying background level of CH4 concentrations within a range comprised between 240 and 650 pptv. [ABSTRACT FROM AUTHOR]

The deuterium to hydrogen (D/H) ratio is commonly used to investigate the history of water on Mars, yet the mechanisms controlling present‐day HDO behavior are poorly understood. Significant variations of the D/H ratio were first predicted on the basis of a 3D global climate model, which were later confirmed by ground‐based observations. This behavior, consisting of lower HDO/H2O ratios in the colder regions of Mars, is related to the isotopic fractionation occurring at condensation. We leverage this previous effort and present an updated implementation, using the modern version of the model, that remains in agreement with the older version. We explore the impact of the global dust storm (GDS) that occurred during Martian year 34 (MY34) on HDO. Our simulations indicate that HDO is on average 40% more abundant at 100 km during the MY34 GDS year than during a regular year, with likely large consequences for the escape flux of water that year. Plain Language Summary: HDO, the semi‐heavy isotope of water, when compared to water, is a good indicator of how much water has been escaping from the atmosphere of Mars over the ages. Ultimately, it can be used to estimate the past reservoir of water available on Mars in its early youth. Because HDO has a slightly higher molecular mass compared to H2O, condensation induces an enrichment of HDO in the ice phase compared with the vapor phase. This subsequently causes spatial and temporal variations of the deuterium to hydrogen ratio. We use a global circulation model to simulate the HDO cycle in the atmosphere. Our model is an upgrade of the previous model presented in Montmessin et al. (2005, Journal of Geophysical Research, 110(E3), E10004. doi:10.1029/2004JE002357). We then simulate the effect of the global dust storm that affected Mars during the summer of 2018, and show that it should have had a strong impact on the vertical distribution of HDO, allowing it to reach higher altitudes. Such simulations are intended to be compared with observations from the Trace Gas Orbiter, currently in orbit around Mars. Key Points: We reimplemented the HDO cycle in a more recent version of the Laboratoire de Météorologie Dynamique Mars global climate modelWe reproduce the observed gradient of the deuterium to hydrogen ratio between cold and warm regionsThe global dust storm of Martian year 34 has a strong effect on the vertical distribution of HDO [ABSTRACT FROM AUTHOR]

The Perseverance rover is carrying out an original acoustic experiment on Mars: the SuperCam microphone records the spherical acoustic waves generated by laser sparks at distances from 2 m to more than 8 m. These N-shaped acoustic waves scatter from the multiple local heterogeneities of the turbulent atmosphere. Therefore, large and random fluctuations of sound travel time and intensity develop as the waves cross the medium. The variances of the travel times and the scintillation index (normalized variance of the sound intensity) are studied within the mathematical formalism of the propagation of spherical acoustic waves through thermal turbulence to infer statistical properties of the Mars atmospheric temperature fluctuation field. The comparison with the theory is made by simplifying assumptions that do not include wind fluctuations and diffraction effects. Two Earth years (about one Martian year) of observations acquired during the maximum convective period (10:00–14:00 Mars local time) show a good agreement between the dataset and the formalism: the travel time variance diverges from the linear Chernov solution exactly where the density of occurrence of the first caustic reaches its maximum. Moreover, on average, waves travel faster than the mean speed of sound due to a fast path effect, which is also observed on Earth. To account for the distribution of turbulent eddies, several power spectra are tested and the best match to observation is obtained with a generalized von Karman spectrum with a shallower slope than the Kolmogorov cascade, ϕ (k) ∝ (1 + k 2 L 2) − 4 / 3 . It is associated with an outer scale of turbulence, L, of 11 cm at 2 m above the surface and a standard deviation of 6 K over 9 s for the temperature. These near-surface atmospheric properties are consistent with a weak to moderate wave scattering regime around noon with little saturation. Overall, this study presents an innovative and promising methodology to probe the near-surface atmospheric turbulence on Mars. [ABSTRACT FROM AUTHOR]

After launching from the martian surface via the Mars Ascent Vehicle (MAV), the MAV and the Orbiting Sample (OS) capsule containing the samples collected on Mars by the Perseverance rover are to be identified by the Narrow Angle Camera (NAC) on the Earth Return Orbiter (ERO) spacecraft in order to determine the exact orbit of the capsule before rendezvous. To ensure detection of the OS, noise and straylight contributions to the NAC must be well characterized. Here, we assess the radiometric environment at Mars likely to be encountered by the NAC—from the surface through the middle atmosphere—using the High Resolution Stereo Camera (HRSC) onboard Mars Express (MEx) and the Mars Climate Sounder (MCS) onboard the Mars Reconnaissance Orbiter (MRO). The results show that the radiance values in general tend to increase as phase angle increases, as the season progresses from L s = 60° to L s = 230°, and as altitude decreases. We compare HRSC and MCS profiles where observing conditions were similar and find good agreement. At specific latitudes, high-altitude aerosols are present in 1–5% of observations and significantly increase the worst-case radiance contribution above 50 km. We construct envelope profiles from the maximum radiances at 5 km intervals from 0 to 90 km that provide important input for straylight calculations of the NAC and for the validation of models that may be used as input for straylight calculations. [ABSTRACT FROM AUTHOR]

Global climate modeling of the Mars water cycle is usually performed at relatively coarse resolution ( 200 − 300 km ), which may not be sufficient to properly represent the impact of waves, fronts, topography effects on the detailed structure of clouds and surface ice deposits. Here, we present new numerical simulations of the annual water cycle performed at a resolution of 1° × 1° (∼ 60 km in latitude). The model includes the radiative effects of clouds, whose influence on the thermal structure and atmospheric dynamics is significant, thus we also examine simulations with inactive clouds to distinguish the direct impact of resolution on circulation and winds from the indirect impact of resolution via water ice clouds. To first order, we find that the high resolution does not dramatically change the behavior of the system, and that simulations performed at ∼ 200 km resolution capture well the behavior of the simulated water cycle and Mars climate. Nevertheless, a detailed comparison between high and low resolution simulations, with reference to observations, reveal several significant changes that impact our understanding of the water cycle active today on Mars. The key northern cap edge dynamics are affected by an increase in baroclinic wave strength, with a complication of northern summer dynamics. South polar frost deposition is modified, with a westward longitudinal shift, since southern dynamics are also influenced. Baroclinic wave mode transitions are observed. New transient phenomena appear, like spiral and streak clouds, already documented in the observations. Atmospheric circulation cells in the polar region exhibit a large variability and are fine structured, with slope winds. Most modeled phenomena affected by high resolution give a picture of a more turbulent planet, inducing further variability. This is challenging for long-period climate studies. [ABSTRACT FROM AUTHOR]

• Development of a new cloud model for Venus. • Modal Aerosol Dynamics applied to microphysical processes on Venus. • All processes behave as expected in the tested cases. For decades, clouds have remained a central open question in understanding the climate system of Venus. We have developed a new microphysical model for the clouds of Venus that we describe in this paper. The model is a modal aerosol dynamical model that treats the formation and evolution of sulfuric acid solution droplets with a moderate computational cost. To this end, the microphysical equations are derived to describe the evolution of the size distribution of the particles using the moments of the distribution. We describe the derivation of the equations and their implementation in the model. We tested each microphysical process of the model separately in conditions of the Venus' atmosphere and show that the model behaves in a physically sound manner in the tested cases. The model will be coupled in the future with a Venus Global Climate Model and used for elucidating the remaining mysteries. [ABSTRACT FROM AUTHOR]

We present unique polarization data from the SPICAV-IR spectrometer onboard ESA׳s Venus Express (VEx) spacecraft and a first retrieval of cloud parameters. The polarization data have been collected from 2006 to 2010, and cover mostly the northern hemisphere, in the 0.65 to 1.7 μ m spectral range. They contain information about latitudinal and longitudinal variations in the properties of Venus clouds and hazes, and about temporal variations in these properties. The degree of polarization measured on a few test orbits is in agreement with previous observations from the ground and from Pioneer Venus . Using numerical modeling to interpret the nadir observations, we retrieve mean values of r eff ~ 1 μ m and ν eff ~ 0.07 for, respectively, the effective radius and variance of the cloud particle size distribution and a refractive index n r = 1.42 ± 0.02 at λ = 1.101 μ m . We also derive an upper limit τ h = 0.17 at λ = 1.101 μ m for the haze optical thickness at high latitudes. All these values are in good agreement with previous determinations. [ABSTRACT FROM AUTHOR]

We present the Infrared spectrometer of SuperCam Instrument Suite that enables the Mars 2020 Perseverance Rover to study remotely the Martian mineralogy within the Jezero crater. The SuperCam IR spectrometer is designed to acquire spectra in the 1.3– 2. 6 μ m domain at a spectral resolution ranging from 5 to 20 nm. The field-of-view of 1.15 mrad, is coaligned with the boresights of the other remote-sensing techniques provided by SuperCam: laser-induced breakdown spectroscopy, remote time-resolved Raman and luminescence spectroscopies, and visible reflectance spectroscopy, and micro-imaging. The IR spectra can be acquired from the robotic-arm workspace to long-distances, in order to explore the mineralogical diversity of the Jezero crater, guide the Perseverance Rover in its sampling task, and to document the samples' environment. We present the design, the performance, the radiometric calibration, and the anticipated operations at the surface of Mars. • We present the SuperCam infrared spectrometer operating on board the Perseverance Rover • It covers the 1.3–2.6 μ m bandpass, at ∼ 10 and 5 nm spectral resolution and sampling • We describe the design, operation, and the data structure of the instrument [ABSTRACT FROM AUTHOR]

Thermal tides in the Martian atmosphere are analyzed using temperature profiles retrieved from nadir observations obtained by the TIRVIM Fourier‐spectrometer, part of the Atmospheric Chemistry Suite onboard the ExoMars Trace Gas Orbiter. The data is selected near the northern summer solstice at solar longitude (LS) 75°–105° of Martian Year 35. The observations have a full local time coverage, which enables analyses of daily temperature anomalies. The observed zonal mean temperature is lower by 4–6 K at ∼100 Pa, but higher toward the summer pole, compared to the Laboratoire de Météorologie Dynamique (LMD) Mars General Circulation Model (GCM). Wave mode decomposition shows dominant diurnal tide and important semi‐diurnal tide and diurnal Kelvin wave, with maximal amplitudes of 5, 3, and 2.5 K, respectively, from tens to hundreds of Pa. The results generally agree well with the LMD Mars GCM, but with noticeable earlier phases of diurnal (∼1 hr) and semi‐diurnal (∼3 hr) tides. Plain Language Summary: Unlike the Earth, daily temperature variation on Mars is as large as tens of degrees because of its thin atmosphere. The sunlight absorbed by the Martian surface and dust in the atmosphere leads to dramatic temperature increase in the lower atmosphere during daytime. Such large and regular changes can trigger temperature waves, and some modes of them can propagate into higher altitudes, where they become the major factor controlling the daily temperature variation. In this work, temperature profiles obtained using thermal‐infrared spectra are analyzed. Zonal mean temperature is compared with numerical simulations of the Martian atmosphere. Different types of the wave modes are computed through decomposition. Results from the observation agree well with model prediction when the observation mechanisms are taken into consideration. Estimation of the strength of these waves can be improved in the future with improved design of observation strategies. Key Points: Thermal tides in the Martian atmosphere are investigated using temperature profiles retrieved from TIRVIM nadir observationsDiurnal tide dominates daily temperature variations; semi‐diurnal tide and diurnal Kelvin wave are also importantObservations agree well with numerical simulations, but suggest phases of diurnal and semi‐diurnal tides earlier than predicted [ABSTRACT FROM AUTHOR]

Mars northern polar latitudes are known to harbor an enhanced 3 μ m spectral signature when observed from orbit. This may indicate a greater amount of surface adsorbed or bound water, although it has not yet been possible to easily reconcile orbital observations with ground measurements by Phoenix. Here we re-analyzed OMEGA/Mars Express observations acquired during the Northern summer to further characterize this 3 μ m absorption band increase. We identify the presence of a new specific spectral signature composed of an additional narrow absorption feature centered at 3.03 μ m coupled with an absorption at λ ≥ 3. 8 μ m. This signature is homogeneously distributed over a high-albedo open ring surrounding the circumpolar low-albedo terrains between ∼ 68°N and 76°N and ∼ 0°E and 270°E. This location includes the Phoenix landing site. This feature shows no time variability and can be confidently attributed to a seasonally stable surface component. All together, the stability, spectral shape and absence of significant correlation with other signatures in the 1–2.5 μ m range discard interpretations relying on water ice or easily exchangeable adsorbed water. Sulfates, notably anhydrite, provide interesting comparisons to several sections of the spectrum. Analogies with Earth samples also show that the spectral signature could result from a latitudinal modification of the hydration state and/or grains size of salts contaminants. While the exact full spectral shape cannot be easily reproduced, plausible explanations to this observation seem to involve geologically recent water alteration at high northern latitudes. • Using OMEGA data, we have identified a new spectral signature composed of a narrow 3 μ m band associated with a 4 μ m absorption. • This signature is observed exclusively over an open-ring area surrounding the North polar dunes between 68°N and 76°N. • This observation may indicate a specific physical or chemical alteration potentially involving sulfates in a polar environment. [ABSTRACT FROM AUTHOR]

In 2020, hydrogen chloride (HCl) in the gas phase was discovered in the atmosphere of Mars with the Atmospheric Chemistry Suite (ACS) onboard the Trace Gas Orbiter (TGO) mission (Korablev et al., 2021). Its volume mixing ratio (VMR) shows a seasonal increase of up to 5 ppbv during the perihelion season, followed by a sudden drop to undetectable levels, contradicting modelling estimates of the HCl lifetime of several months. In the Earth's stratosphere, heterogeneous uptake of HCl onto water ice is known to be a major sink for this species. This reaction is now also considered when modelling HCl abundances in the Martian atmosphere. In this work, we use simultaneous measurements of water ice and HCl obtained by the ACS instrument to find particular structures in the vertical profiles as detached gas layers at ice-free altitudes ("ice-holes"). From these particular examples we conclude that the heterogeneous uptake of HCl onto water ice operates on Mars and is a fast mechanism regulating the HCl abundance in the atmosphere of Mars. • Simultaneous vertical profiles of water ice and HCl analysed over 2.5 Martian years. • HCl gas layers at ice-free altitudes reveal local anticorrelation of HCl vs water ice. • Heterogeneous uptake of HCl onto water ice rapidly regulates HCl abundance. [ABSTRACT FROM AUTHOR]

Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). In this study, we review the related works on the past climate of Mars, its evolution, and the present climate and weather to describe the scientific goals and strategies of the MMX mission regarding the evolution of the Martian surface environment. The MMX spacecraft will retrieve and return a sample of Phobos regolith back to Earth in 2029. Mars ejecta are expected to be accumulated on the surface of Phobos without being much shocked. Samples from Phobos probably contain all types of Martian rock from sedimentary to igneous covering all geological eras if ejecta from Mars could be accumulated on the Phobos surface. Therefore, the history of the surface environment of Mars can be restored by analyzing the returned samples. Remote sensing of the Martian atmosphere and monitoring ions escaping to space while the spacecraft is orbiting Mars in the equatorial orbit are also planned. The camera with multi-wavelength filters and the infrared spectrometer onboard the spacecraft can monitor rapid transport processes of water vapor, dust, ice clouds, and other species, which could not be traced by the previous satellites on the sun-synchronous polar orbit. Such time-resolved pictures of the atmospheric phenomena should be an important clue to understand both the processes of water exchange between the surface/underground reservoirs and the atmosphere and the drivers of efficient material transport to the upper atmosphere. The mass spectrometer with unprecedented mass resolution can observe ions escaping to space and monitor the atmospheric escape which has made the past Mars to evolve towards the cold and dry surface environment we know today. Together with the above two instruments, it can potentially reveal what kinds of atmospheric events can transport tracers (e.g., H2O) upward and enhance the atmospheric escape. [ABSTRACT FROM AUTHOR]

We present the first water vapor profiles encompassing the upper mesosphere of Mars, 100–120 km, far exceeding the maximum altitudes where remote sensing has been able to observe water to date. Our results are based on solar occultation measurements by Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO). The observed wavelength range around 2.7 μm possesses strong CO2 and H2O absorption lines allowing sensitive temperature and density retrievals. We report a maximum H2O mixing ratio varying from 10 to 50 ppmv at 100–120 km during the global dust storm (GDS) of Martian Year (MY) 34 and around southern summer solstice of MY 34 and 35. During other seasons water remains persistently below ∼2 ppmv. We claim that contributions of the MY34 GDS and perihelion periods into the projected hydrogen escape from Mars are nearly equivalent. Plain Language Summary: We report regular events of high abundances of the water vapor (H2O) in the upper atmosphere of Mars (100–120 km). So far, any water enrichment has not been revealed by remote sensing at such high altitudes. Higher than 80 km, solar light breaks water vapor molecules into H and O atoms, which may reach the exosphere and escape the planet. When Mars is closer to the Sun (the perihelion season), the atmosphere's circulation intensifies, causing increased dust activity with global dust storms (GDS), occurring every 3–4 Mars years. We observed during the second halves of Martian years 34 and 35 (2018–2020), including one GDS and two perihelion seasons. We report that the maximum water relative abundance reaches 10–50 parts per million in volume (ppmv) at 100–120 km during the GDS and every perihelion season. These high values indicate that the Martian atmosphere above 100 km regularly hosts large amounts of water, facilitating the long‐term escape of water from the planet. Key Points: Water abundances are reported in a previously unexplored altitude range: from 100 to 120 kmThe observed GDS (MY34) and two perihelion seasons (MY34, 35) reveal the H2O content around 10–50 parts per million by volume at 100–120 kmContributions of the MY34 GDS and perihelion periods into the projected hydrogen escape from Mars are nearly equivalent [ABSTRACT FROM AUTHOR]

In situ measurements by an atmospheric entry probe allow for sounding and investigating atmospheric composition, structure and dynamics deep into the atmosphere of a Giant planet. In this paper, we describe an Atmospheric Structure Instrument (ASI) for an entry probe at Uranus and/or Neptune. The scientific objectives, the measurements and the expected results are discussed in the framework of a future opportunity for an NASA-ESA joint mission to the Ice Giant planets. [ABSTRACT FROM AUTHOR]

Stellar occultation is a powerful method to study vertical structure of the Venus night mesosphere. The UV channel of SPICAV spectrometer, operated in 2006–2014 on board ESA's Venus Express orbiter, allowed retrieval profiles of atmospheric gases (CO 2 , SO 2 , and O 3) and aerosols. It was also able to register different UV emissions around Venus (nitric oxide airglow, Lyman-α) overlapping the absorption features at 120–300 ​nm. Several calibration steps convert the raw data to atmospheric transmission spectra used for the retrievals. The systematic errors of resulted gaseous concentrations mainly relate to: (i) an uncertainty of the wavelength to pixel assignment; (ii) a portion of emitting light contaminating the analyzed transmission spectra. In the present paper, we have tested a new method of the wavelength-to-pixel assignment based on the spectral features of measured stars. Secondly, using imaging capabilities of the instrument, we have demonstrated an accurate separation between different kinds of registered signal: extended UV nightglow, light from a point star, transmitted through the atmosphere, and, sometimes, solar light, scattered by Venus dusk. The efficiency of two approaches performing the separation was studied. As a result, corrected transmission spectra provided retrievals of gaseous concentrations with 20–40% higher precision respectively to those processed in previous SPICAV stellar occultation studies (Montmessin et al., 2011, Icarus 216, 82; Piccialli et al., 2015, Planet. Space Sci. 113–114, 321; Belyaev et al., 2017, Icarus 294, 58). • Systematic errors in retrievals of the SPICAV UV stellar occultation data were analyzed. • Errors relate to a wavelength to pixel assignment and an overlap of point and extended UV sources spectra. • A new method of the wavelength assignment is based on the stellar spectral features. • Two methods separating spectra of a star and extended light sources were studied. • Corrected spectra provide a 20–40% higher precision of stellar occultation retrievals. [ABSTRACT FROM AUTHOR]

Ozone (O 3) is important in the stabilisation of CO 2 in the Martian atmosphere and thus it is important to study the spatio-temporal variability of O 3 . We retrieve two years of total columnar O 3 from raw spectral data provided by the SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) instrument aboard the Mars Express. The seasonal variability is studied in tropical, mid- and high latitudes and is compared with simulations by a photochemical coupled general circulation model (GCM). The high latitudes exhibit the largest seasonal variations in O 3 , with a winter high and a summer low and a comparison with GCM results is good in general. We have studied the correlation of O 3 with dust, retrieved simultaneously from SPICAM observations. In southern tropical latitudes, the columnar O 3 is seen to increase during a global dust storm year (Martian year (MY) 28) compared to the O 3 column values during a year without global dust storm (MY27), although the water vapour column between these years remains unchanged. This indicates the radiative impact of dust on O 3 and its retrieval. We also study the ozone–carbon monoxide correlation as a tracer of dynamics. The dynamical contribution to the O 3 column is found to be the highest during winter over the southern polar region. [ABSTRACT FROM AUTHOR]

We report a new set of stellar occultation measurements for nightside temperature profiles made by the Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph that provide evidence for a recurring layer of warm air between 70 and 90 km altitudes in the nightside mesosphere of Mars during Ls = 0–180° in Martian Year 33–34. The nightside profiles reveal a recurring peak of atmospheric temperature around 80 km over the equator to the middle latitudes in the northern hemisphere. The predictions of the Mars Climate Database have a warm layer with much smaller amplitudes. The observed peak amplitudes are larger than those predicted by the model by up to 90 K. Wavenumber‐3 structures are seen in the warm layer that are potentially signatures of thermal tides or stationary planetary waves, with amplitudes two times larger than predicted. Plain Language Summary: The Mars middle atmosphere is an intermediate region with rich and complex dynamics influenced by the underlying lower atmosphere and the overlying upper atmosphere. We report a new set of stellar occultation measurements made by the MAVEN/IUVS that provide evidence for a warm layer between 70 and 90 km altitude in the nightside mesosphere of Mars during Ls = 0–180° in Marian Year 33–34. Key Points: MAVEN/IUVS revealed a warm layer between 70 and 90 km altitude in the nightside on Mars during Ls = 0–180° in Martian Year 33–34The observed peak temperature amplitudes of nightside profiles are higher than those predicted by the model by up to 90 KLongitudinal wavenumber‐3 structures are seen in the warm layer, two times larger amplitudes than predicted [ABSTRACT FROM AUTHOR]

We report a new set of stellar occultation measurements for nightside temperature profiles made by the Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph that provide evidence for a recurring layer of warm air between 70 and 90 km altitudes in the nightside mesosphere of Mars during Ls = 0–180° in Martian Year 33–34. The nightside profiles reveal a recurring peak of atmospheric temperature around 80 km over the equator to the middle latitudes in the northern hemisphere. The predictions of the Mars Climate Database have a warm layer with much smaller amplitudes. The observed peak amplitudes are larger than those predicted by the model by up to 90 K. Wavenumber‐3 structures are seen in the warm layer that are potentially signatures of thermal tides or stationary planetary waves, with amplitudes two times larger than predicted. Plain Language Summary: The Mars middle atmosphere is an intermediate region with rich and complex dynamics influenced by the underlying lower atmosphere and the overlying upper atmosphere. We report a new set of stellar occultation measurements made by the MAVEN/IUVS that provide evidence for a warm layer between 70 and 90 km altitude in the nightside mesosphere of Mars during Ls = 0–180° in Marian Year 33–34. Key Points: MAVEN/IUVS revealed a warm layer between 70 and 90 km altitude in the nightside on Mars during Ls = 0–180° in Martian Year 33–34The observed peak temperature amplitudes of nightside profiles are higher than those predicted by the model by up to 90 KLongitudinal wavenumber‐3 structures are seen in the warm layer, two times larger amplitudes than predicted [ABSTRACT FROM AUTHOR]

We describe and document the physics packages in the legacy NASA/Ames Mars Global Climate Model, present simulations of the seasonal water cycle and how it compares with observations, assess the role of radiatively active clouds on the water cycle and planetary eddies, and discuss the strengths and weakness of the model and the implication for future efforts. The physics packages we describe include the treatment of surface properties, the ground temperature model, planetary boundary layer scheme, sublimation physics, cloud microphysics, the use of a moment method for tracer transport, a semi-interactive dust tracking scheme, and a two-stream radiative transfer code based on correlated-k's. With virtually no tuning of the water cycle and assuming the north polar residual water ice cap is the only source of water we find the model gives a reasonably good simulation of the present seasonal water cycle. No persistent clouds form over the residual cap, seasonal variations in column vapor abundances are similar to those observed, the aphelion cloud belt has about the right opacity, and surface and air temperatures are in reasonably good agreement with observations. The radiative effect of clouds does not significantly alter the seasonal and spatial variation of the moisture fields, though the clouds are thicker and the atmosphere somewhat wetter. As others have found cloud radiative forcing amplifies the mean meridional circulation, transient baroclinic eddies, and global thermal tides. However, it also changes the characteristics of forced stationary waves in ways that are not straightforward to understand. The main weakness of the model, we believe, is sluggish vertical mixing. Water is not transported high enough in the model and as a consequence the water cycle is too dry, the aphelion cloud belt is too low, and the mean meridional circulation is too shallow. These, we feel, could be remedied by some combination of non-local mixing, deep mountain-induced circulations, better horizontal and vertical resolution, and/or gravity wave drag. Efforts are now underway to study these issues as we are transitioning away from our legacy code to one with a more modern dynamical core. • Full documentation of the NASA/Ames Legacy Mars Global Circulation Model is provided. • Simulations of the present water cycle are in reasonable agreement with available observations. • The radiative effects of clouds on each of major component of the global circulation are assessed. • The overall dryness of the model may be caused by weak vertical transport. [ABSTRACT FROM AUTHOR]

The Compact Reconnaissance Imaging Spectral Mapper (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) obtains pole-to-pole observations (i.e., full MRO orbits) of vertical profiles for visible/near-IR spectra (λ = 0.4–4.0 μm), which are ideally suited to identifying the composition and particle sizes of Mars ice and dust aerosols over 50–100 km altitudes in the Mars mesosphere. Within the coverage limitations of the CRISM limb data set, a distinct compositional dichotomy is found in Mars mesospheric ice aerosols. CO 2 ice clouds appear during the aphelion period of Mars orbit (Solar Longitudes, L s ∼ 0–160°) at low latitudes (∼20S–10N) over specific longitude regions (Meridiani, Valles Marineris) and at typical altitudes of 55–75 km. Apart from faint water ice hazes below 55 km, mesospheric H 2 O ice clouds are primarily restricted to the perihelion orbital range (L s ∼160 – 350°) at northern and southern mid-to-low latitudes with less apparent longitudinal dependences. Mars mesospheric CO 2 clouds are presented in CRISM spectra with a surprisingly large range of particle sizes (cross section weighted radii, R eff = 0.3 to 2.2 μm). The smaller particle sizes (R eff ≤1 μm) appear concentrated near the spatial (latitude and altitude) boundaries of their global occurrences. CRISM spectra of mesospheric CO 2 clouds also show evidence of iridescence, indicating very narrow particle size distributions (effective variance, V eff ∼ 0.03) and so very abrupt CO 2 cloud nucleation. Furthermore, these clouds are sometimes accompanied by altitude coincident peaks in 1.27 μm O 2 dayglow, which indicates very dry, cold regions of formation. Mesospheric water ice clouds generally exhibit small particle sizes (R eff = 0.1–0.3 μm), although larger particle sizes (R eff = 0.4–0.7 μm) appear infrequently. On average, water ice cloud particle sizes decrease with altitude over 50–80 km in the perihelion mesosphere. Water ice mass appears similar in clouds over a large range of observed cloud particle sizes, with particle number densities increasing to ∼10 cm−3 for R eff = 0.2 μm. Near coincident Mars Climate Sounder (MCS) temperature and aerosol profile measurements for a subset of CRISM mesospheric aerosol measurements indicate near saturation (H 2 O and CO 2) conditions for ice clouds and distinct mesospheric temperature increases associated with mesospheric dust loading. Dayside (3 pm) mesospheric CO 2 clouds with larger particle sizes (R eff ≥0.5 μm) scatter surface infrared emission in MCS limb infrared radiances, as well as solar irradiance in the MCS solar band channel. Scattering of surface infrared emission is most strikingly presented in nighttime (3 am) MCS observations at 55–60 km altitudes, indicating extensive mesospheric nighttime CO 2 clouds with considerably larger particle sizes (R eff ∼7 μm). Mesospheric CO 2 ice clouds present cirrus-like waveforms over extensive latitude and longitude regions (10°×10°), as revealed in coincident Mars Color Imager (MARCI) nadir imaging. Solar tides, gravity waves, and the large orbital variation of the extended thermal structure of the Mars atmosphere influence all of these behaviors. Mesospheric dust aerosols appear infrequently over the non-global (planet encircling) dust storm era of the CRISM limb data set (2009–2016), and exhibit smaller particle sizes (R eff = 0.2–0.7 μm) relative to dust in the lower atmosphere. One isolated case of an aphelion (L s = 96°) mesospheric dust layer with large dust particle sizes (R eff ∼2 μm) over Syria Planum may reflect high altitude, non-local transport of dust over elevated regions. • Characterization of dust and Ice aerosol distributions in the Mars mesosphere • Characterization of Mar mesospheric aerosol compositions and particle sizes • An orbital dichotomy in Mars mesospheric ice cloud composition • Large CO 2 ice cloud particles in the nightside Mars mesosphere • Definition of CO 2 ice cloud iridescence in the Mars mesosphere [ABSTRACT FROM AUTHOR]

Highlights • First detection of cloud top ozone in Venus atmosphere (about 1000 times less than Earth). • Ozone presence is restricted to high latitudes (polewards of 50°) in both hemispheres. • Measurements are qualitatively supported by our 3D photochemical model. Abstract After the first sporadic detections of an ozone (O 3) nighttime layer in the 90–100 km altitude range (Montmessin et al., 2011), we report here the discovery of another, permanent ozone layer on Venus, restricted to high latitudes (polewards of 50° both N and S) and located at the upper cloud level near 70 km. This detection was performed during a reanalysis of the whole SPICAV-UV nadir dataset through UV absorption near 250 nm in the backscattered solar light. The O 3 volume mixing ratio peaks in the 10–20 ppbv range, yielding observable column densities in the 0.1–0.5 Dobson units (DU), comparable to nominal values on Mars but much smaller than for Earth (∼ 300 DU). These measurements are supported by our 3D-photochemical model coupled with the LMD-IPSL GCM (Lebonnois et al., 2010), which indicates that the ozone layer identified by SPICAV results from downward transport of O 2 (∼ 50 ppmv) molecules over the poles by the mean meridional circulation. Our findings do not contradict previous upper limits (< 2 ppmv) based on O 2 measurements (Mills, 1999), since they were restricted to lower latitudes only. [ABSTRACT FROM AUTHOR]

Abstract: In September 2017, an active region of the Sun produced a series of strong flares and a coronal mass ejection that swept past Mars producing enhanced ionization and heating in the upper atmosphere. Emissions from atmospheric hydrogen Lyman‐α were also enhanced at Mars. Temperatures derived from neutral species scale heights were used in conjunction with the H Lyman‐α observations to simulate the effects of this space weather event on Martian hydrogen properties in the exosphere. It was found that hydrogen abundance in the upper atmosphere decreased by ~25% and that the H escape rate increased by a factor of 5, mainly through an increase in upper atmospheric temperature. This significant escape rate variation is comparable to seasonally observed trends but occurred at much shorter timescales. Such solar events would statistically impact extrapolation of Martian water loss over time. [ABSTRACT FROM AUTHOR]

The sounds of the Ingenuity Helicopter flying in the Martian atmosphere are among the most notable recordings of the microphone on the SuperCam instrument on the Mars 2020 Perseverance Rover. Distinct acoustic signatures of the helicopter were recorded on the 4th, 5th, 6th, and 8th flights: prior to this, simultaneous microphone and helicopter operations had not been verified in the testbed, and generally since these early flights the helicopter has been too far away for its emissions to be detectable given CO 2 absorption in the Mars atmosphere. The detected signatures are around 84 ​Hz and (occasionally) at 168 ​Hz, at the blade crossing frequency and its first harmonic. Several higher harmonics were prominent in hover tests in short-range recordings in a test chamber on Earth; these are attenuated by CO 2 absorption at the 50m-plus ranges on Mars. Doppler shift of the 84 ​Hz signal can be measured and is consistent with the trajectory measured with Ingenuity's navigation camera and inertial navigation unit, and documented by Perseverance's cameras. A striking feature of the sound recordings is an unanticipated deep modulation of the signals with nulls spaced by around 15–20s, superposed on the simple and expected decline in amplitude with distance. We have evaluated and rejected models of multipath sound interference as requiring implausibly strong near-surface temperature gradients. We find instead that the modulation appears to be the signature of a slight asynchrony between the rotation rates of the two coaxial rotors, such that the blade-crossing azimuth rotates slowly during flight, resulting in a 'lighthouse' sweeping of the radiated sound pattern. Analysis of blade orientations seen in the shadow of the helicopter observed in down-looking navigation images supports this model. • Documents sound recordings of Ingenuity helicopter flights on Mars. • Demonstrates acoustic data on rover are diagnostic of flights e.g. via Doppler effect. • Unexpected drops in loudness with 10–20s period may relate to slightly mismatched rotor speeds. • Helicopter shadow images show loudness drops correspond to blade-crossings aimed at rover. [ABSTRACT FROM AUTHOR]

The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere. [ABSTRACT FROM AUTHOR]

Recent observations of the Martian hydrogen corona in the UV H Ly-alpha emission by the Hubble Space Telescope (HST) (Clarke et al., 2014) and the SPICAM UV spectrometer on Mars Express (Chaffin et al., 2014) reported its rapid change by an order of magnitude over a short few months period in 2007 (MY28), which is inconsistent with the existing models. One proposed explanation of the observed increase of the coronal emission is that during the global dust storm water vapor from the lower atmosphere can be transported to higher altitudes, where its photodissociation rate by near-UV sunlight increases, providing an additional source of hydrogen for the upper atmosphere. In this work we study the water vapor vertical distribution in the middle atmosphere of Mars during the 2007 global dust storm based on solar occultation measurements by the SPICAM IR spectrometer onboard the Mars-Express spacecraft. The vertical profiles of H 2 O density and mixing ratio have been obtained for solar longitudes Ls = 255°–300° in MY28. In the Northern hemisphere from Ls = 268° to Ls = 285° the H 2 O density at altitudes of 60–80 km increased by an order of magnitude. During the dust storm the profiles extended up to 80 km, with an H 2 O density exceeding 10 10 molecules/cm 3 (mixing ratio ≥200 ppm). Two maxima of the H 2 O density were detected. The largest H 2 O densities observed at latitudes higher than 60°N, over Ls = 269°–275°, do not directly correlate with the aerosol loading and likely relate to the downwelling branch of the meridional circulation that was intensified during the dust storm, and transported water from the Southern hemisphere to high northern latitudes. The second smaller maximum coincides with the high dust loading at middle northern latitudes. The comparison with geographically close observations in the quiet Mars year MY32, when the H 2 O content in the Northern hemisphere did not exceed 2 × 10 10 molecules/cm 3 and 50 ppm at 60 km, showed that the global dust storm was a unique event. The situation was different in the Southern hemisphere. During the dust storm the water density at 50–80 km increased by a factor of 4–5 with a mixing ratio >100 ppm, well correlated with the aerosol vertical extension. A somewhat weaker increase of the H 2 O density by a factor of 2–3 with a mixing ratio > 100 ppm was also observed during MY32 starting from Ls = 260°, suggesting a seasonal repeatability. The observed amount of water at high altitudes in both hemispheres can produce a large increase in the H escape rate on a timescale of weeks, as was shown in the photochemical modeling by Chaffin et al. (2017). Future modeling would be necessary to separate the seasonal and the dust storm contributions to the hydrogen escape. [ABSTRACT FROM AUTHOR]

The Venus International Reference Atmosphere (VIRA) model contains tabulated values of temperature and number densities obtained by the experiments on the Venera entry probes, Pioneer Venus Orbiter and multi-probe missions in the 1980s. The instruments on the recent Venus Express orbiter mission generated a significant amount of new observational data on the vertical and horizontal structure of the Venus atmosphere from 40 km to about 180 km altitude from April 2006 to November 2014. Many ground based experiments have provided data on the upper atmosphere (90–130 km) temperature structure since the publication of VIRA in 1985. The "Thermal Structure of the Venus Atmosphere" Team was supported by the International Space Studies Institute (ISSI), Bern, Switzerland, from 2013 to 2015 in order to combine and compare the ground-based observations and the VEx observations of the thermal structure as a first step towards generating an updated VIRA model. Results of this comparison are presented in five latitude bins and three local time bins by assuming hemispheric symmetry. The intercomparison of the ground-based and VEx results provides for the first time a consistent picture of the temperature and density structure in the 40 km–180 km altitude range. The Venus Express observations have considerably increased our knowledge of the Venus atmospheric thermal structure above ∼40 km and provided new information above 100 km. There are, however, still observational gaps in latitude and local time above certain regions. Considerable variability in the temperatures and densities is seen above 100 km but certain features appear to be systematically present, such as a succession of warm and cool layers. Preliminary modeling studies support the existence of such layers in agreement with a global scale circulation. The intercomparison focuses on average profiles but some VEx experiments provide sufficient global coverage to identify solar thermal tidal components. The differences between the VEx temperature profiles and the VIRA below 0.1 mbar/95 km are small. There is, however, a clear discrepancy at high latitudes in the 10–30 mbar (70–80 km) range. The VEx observations will also allow the improvement of the empirical models (VTS3 by Hedin et al., 1983 and VIRA by Keating et al., 1985) above 0.03 mbar/100 km, in particular the 100–150 km region where a sufficient observational coverage was previously missing. The next steps in order to define the updated VIRA temperature structure up to 150 km altitude are (1) define the grid on which this database may be provided, (2) fill what is possible with the results of the data intercomparison, and (3) fill the observational gaps. An interpolation between the datasets may be performed by using available General Circulation Models as guidelines. An improved spatial coverage of observations is still necessary at all altitudes, in latitude–longitude and at all local solar times for a complete description of the atmospheric thermal structure, in particular on the dayside above 100 km. New in-situ observations in the atmosphere below 40 km are missing, an altitude region that cannot be accessed by occultation experiments. All these questions need to be addressed by future missions. [ABSTRACT FROM AUTHOR]

The Imaging Ultraviolet Spectrograph (IUVS) is one of nine science instruments aboard the Mars Atmosphere and Volatile and EvolutioN (MAVEN) spacecraft. MAVEN, launched in November 18, 2013 and arriving at Mars in September 2014, is designed to explore the planet's upper atmosphere and ionosphere and examine their interaction with the solar wind and solar ultraviolet radiation. IUVS is one of the most powerful spectrographs sent to another planet, with several key capabilities: (1) separate Far-UV & Mid-UV channels for stray light control, (2) a high resolution echelle mode to resolve deuterium and hydrogen emission, (3) internal instrument pointing and scanning capabilities to allow complete mapping and nearly-continuous operation, and (4) optimization for airglow studies. [ABSTRACT FROM AUTHOR]

The SPICAM IR instrument on the Mars Express mission continuously observes the water vapor in the martian atmosphere starting from 2004 in the 1.38-μm spectral band. The water vapor column abundance is retrieved from nadir observations to characterize its spatial, seasonal and interannual variations. A reference set of SPICAM water vapor column abundances (zonally averaged) covering the time period from 2004 to 2013 (martian years 27–31) is available for a grid of 2° Ls × 2° latitude, along with an average reference map of water vapor abundance combining all the martian years of Mars Express observations. Compared to the previous data retrieval by Fedorova et al. (Fedorova, A., Korablev, O., Bertaux, J.L., Rodin, A., Kiselev, A., Perrier, S. [2006]. J. Geophys. Res. 111, E09S08) the new processing algorithm includes many improvements concerning the calibration and assumed parameters. A major improvement is the account for aerosol scattering based on dust and water ice cloud optical depths measured by THEMIS/Mars Odyssey (Smith, M.D. [2009]. Icarus 202, 444–452). The account for multiple scattering by aerosol particles increases the retrieved water vapor amount by ∼10% in polar areas during summer, and up to 60–70% for large solar zenith angles. The sensitivity of the results to aerosol properties, surface albedo, solar spectrum, and water vapor vertical distribution has also been studied. The retrieved water vapor reveals nominal annual cycle with maximum abundance of about 60–70 pr. μm for the Northern summer and ∼20 pr. μm for the Southern summer. The annual average amount of water has been estimated to be of 10–20 pr. μm, in agreement with other measurements. From year to year the seasonal cycle of water vapor abundance is very stable. An observed decrease during the MY 28 global dust storm cannot be fully attributed to the masking effect of dust, and indicates a real decrease of water amount near or above the surface. No evidence of diurnal variation of column water vapor amount was found, even though the 1.38-μm measurements are sensitive to the few lowermost kilometers above the surface. [ABSTRACT FROM AUTHOR]

Highlights: [•] Water vapour is assimilated into a Mars GCM producing an improved analysis. [•] The analysis reproduces vapour column observations to within the retrieval RMS error. [•] The Hellas and Argyre basins act as regions of increased vapour transport. [•] Net water transport to the northern hemisphere is quantified. [•] Frost deposits around the north polar cap create the observed peak vapour abundances. [Copyright &y& Elsevier]

The ExoMars Trace Gas Orbiter began science operations in April 2018. We report on dataprocessing and analysis for the Atmospheric Chemistry Suite mid-infrared channel(ACSMIR) for the first year of operations. ACS MIR is a cross-dispersion spectrometer operatingin solar occultation mode. Level 0 data (raw detector images) are processed at the SpaceResearch Institute in Moscow (IKI) and spectral and wavenumber calibration areperformed at LATMOS in Paris to produce a level 1 data product of transmissionspectra. Trace gas retrievals are performed at LATMOS with the JPL Gas Fittingsoftware (GFIT). We present retrievals of volume mixing ratio (VMR) verticalprofiles of major gas species (CO, H2O, HDO) and the current state of our searchfor undetected gases (e.g., hydrocarbons, sulphur and chlorine bearing species).Preliminary results show a dependence on latitude for CO above 50 km, a correlationbetween water vapour content and dust loading, and low upper limits for CH4. [ABSTRACT FROM AUTHOR]

The ExoMars Trace Gas Orbiter (TGO), a mission by ESA and Roscosmos, was launched inMarch 2016 and reached its final, near-circular 400 km orbit around Mars in March, 2018. Onboard TGO, the Atmospheric Chemistry Suite (ACS) is a set of three spectrometers includinga thermal-infrared channel, TIRVIM. This Fourier-transform spectrometer covers the range600–6000 cm−1 (1.7–17μm) with a spectral resolution of 1.2 cm−1. We focus here on nadirobservations in the range 600-1300 cm−1, which covers absorption by CO2 (centered at 667cm−1), water ice clouds (centered at 820 cm−1) and dust (centered at 1100 cm−1).The advantage of the TIRVIM data set over previous instruments comes from theTGO orbit, which is not sun-synchronous and was designed to sample a completedaily cycle every 55 days. Hence, TIRVIM has the capacity to uniquely study boththe diurnal and seasonal variability of the thermal structure, dust and ice cloudopacity. We have developed a radiative transfer model coupled to a retrieval algorithm thatexploits TIRVIM spectra to simultaneously retrieve vertical profiles of the temperature from 5 to 45 km, surface temperature, and integrated optical depth of dust and water ice clouds.This algorithm was tested and validated against synthetic observations generated undervarious conditions (local time, seasons, latitude, aerosol load,...). We have thenapplied this algorithm to the first 45 days of TIRVIM data acquired in March-April,2018. The retrieved temperature profiles have been validated against thousandsof co-located measurements acquired by the Mars Climate Sounder around 3amand 3pm, a limb-viewing radiometer onboard Mars Reconnaissance Orbiter. Theagreement between the two data sets is very satisfactory. In particular, the amplitudeof the diurnal thermal tide as seen by MCS is very well captured by TIRVIM atpressures greater than 10 Pa. However, TIRVIM underestimates it in the range 1–10 Pa,which is due to a much poorer vertical resolution in this region (as expected froma nadir-viewing sounder). We will present these results with an emphasis on thediurnal cycle of the atmospheric temperature and the aerosols load, along withcomparisons with predictions from the LMD Mars GCM. Analysis of TIRVIM dataacquired during the dust storm in June-July 2018 is in progress and will also bepresented. Acknowledgements: The ACS experiment is led by IKI in Moscow. We acknowledgesupport by CNES and Roscosmos. [ABSTRACT FROM AUTHOR]

After 15 years in orbit Mars Express remains one of ESA's most scientifically productive Solar System missions whose publication record now exceeds 1200 papers. Characterization of the geological processes on a local-to-regional scale by HRSC, OMEGA and partner experiments on NASA spacecraft has allowed constraining land-forming processes in space and time. Recent results suggest episodic geological activity as well as the presence of large bodies of liquid water in several provinces (e.g. Eridania Planum, Terra Chimeria) in the early and middle Amazonian epoch and formation of vast sedimentary plains north of the Hellas basin. Mars Express observations and experimental teams provided essential contribution to the selection of the Mars-2020 landing sites. Recent discovery of subglacial liquid water underneath the Southern polar cap has proven that the mission science potential is still not exhausted. More than a decade-long record of the atmospheric parameters such as temperature, dust loading, water vapor and ozone abundance, water ice and CO2 clouds distribution, collected by SPICAM, PFS, OMEGA, HRSC and VMC together with subsequent modeling have provided key contributions to our understanding of the martian climate. Recent spectroscopic monitoring of the 2018 dust storm revealed dust properties, their spatial and temporal variations and atmospheric circulation.More than 10,000 crossings of the bow shock by Mars Express allowed ASPERA-3 to characterize complex behavior of the magnetic boundary topology as function of the solar EUV flux. Observations of the ion escape during complete solar cycle revealed important dependencies of the atmospheric erosion rate on parameters of the solar wind and EUV flux and established global energy balance between the solar wind and escaping ion flow. The observations showed that ion escape can be responsible for removal of about 10 mbar over the Mars history that implies existence of other more effective escape channels. The structure of the ionosphere sounded by the MARSIS radar and the MaRS radio science experiment was found to be significantly affected by the solar activity, the crustal magnetic field, as well as by the influx of meteorite and cometary dust. MARSIS and ASPERA-3 observations suggest that the sunlit ionosphere over the regions with strong crustal fields is denser and extends to higher altitudes as compared to the regions with no crustal anomalies. Several models of the upper atmosphere and plasma environment are being developed based on and in support of the collected experimental data. The models aim at creating user-friendly data base of plasma parameters similar to the Mars Climate Database that would be of great service to the planetary community.A significant recent achievement was the flawless transition to the "gyroless" attitude control and operations mode on the spacecraft, that would allow mitigating the onboard gyros aging and extending the mission lifetime. In November 2018 ESA's Science Programme Committee (SPC) confirmed the mission operations till the end of 2020 and notionally approved its extension till the end of 2022. The talk will give the Mars Express status, review the recent science highlights, and outline future plans focusing on synergistic science with TGO. [ABSTRACT FROM AUTHOR]

The ExoMars Trace Gas Orbiter (TGO) is a joint ESA-Roscosmos mission to Mars that has been launched in March 2016. The aerobreaking phase has ended in February 2018 followed by the start of nominal scientific work on the near-circular 400 km orbit in April 2018. The Atmospheric Chemistry Suite (ACS) is a set of three spectrometers (NIR, MIR, and TIRVIM), capable to observe Mars atmosphere in solar occultations, nadir and limb geometry. TIRVIM instrument is a Fourier-spectrometer operating in the 1.7−17 µm spectral range. NIR instrument is a near-infrared spectrometer covering the 0.7-1.6 µm spectral range with a resolving power of ≥20,000. Both spectrometers are operated in solar occultation and nadir modes.The main fraction of aerosols on Mars consists of mineral dust, while H2O ice and CO2 ice crystals are also encountered depending on the season and location. Combination of TIRVIM and NIR spectra obtained in solar occultation mode permits spectral separation of dust and H2O ice clouds particles and retrieval of vertical distribution of aerosols. In this work, we will report analysis of aerosol properties during 2018 dust storm.AcknowledgementsExoMars is the space mission of ESA and Roscosmos. The ACS experiment is led by IKI Space Research Institute in Moscow. The project acknowledges funding by Roscosmos and CNES. Science operations of ACS are funded by Roscosmos and ESA. M. Luginin acknowledges the support from the Ministry of Science and Higher Education of the Russian Federation, grant №14.W03.31.0017. [ABSTRACT FROM AUTHOR]

Our Global Circulation Model (GCM) simulates the atmospheric environment of Mars. It is developped at LMD (Laboratoire de Meteorologie Dynamique, Paris, France) in close collaboration with several teams in Europe (LATMOS, France, University of Oxford, The Open University, the Instituto de Astrofisica de Andalucia), and with the support of ESA (European Space Agency) and CNES (French Space Agency). GCM outputs are compiled to build a Mars Climate Database, a freely available tool useful for the scientific and engineering communities. The Mars Climate Database (MCD) has over the years been distributed to more than 350 teams around the world. The latest series of reference simulations have been compiled in version 5.3 of the MCD which was released in 2017.To summarize, MCD v5.3 provides:- Climatologies over a series of synthetic dust scenarios: standard (climatology) year, cold (ie: low dust), warm (ie: dusty atmosphere) and dust storm, all topped by various cases of Extreme UV solar inputs (low, mean or maximum). These scenarios have been derived from home-made, instrument-derived (TES, THEMIS, MCS, MERs), dust climatology of the last 8 Martian years. The MCD also provides simulation outputs (MY24-33) representative of these actual years.- 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 columns, concentrations of many species: [CO], [O2], [O], [N2], [H2], [O3],...- A high resolution mode which combines high resolution (32 pixel/degree) MOLA topography records and Viking Lander 1 pressure records with raw lower resolution GCM results to yield, within the restriction of the procedure, high resolution values of atmospheric variables.- The possibility to reconstruct realistic conditions by combining the provided climatology with additional large scale and small scale perturbations schemes.At EGU, we will report on the latest improvements in the Mars Climate Database, with comparisons with available measurements from orbit (e.g.: TES, MCS, TGO) and landers (Viking, Phoenix, Curiosity). [ABSTRACT FROM AUTHOR]

We have carried out ground-based seasonal monitoring of hydrogen peroxide on Mars since 2003. This presentation is on the latest set of observations using thermal imaging spectroscopy, with two observations of the planet near opposition, in May 2016 (Ls = 148.5°, diameter = 17") and July 2018 (Ls = 209°, diameter = 23"). Data have been recorded in the 1232 - 1242 cm-1 range (8.1 micron) with the Texas Echelon Cross Echelle Spectrograph (TEXES) mounted at the 3-m Infrared Telescope Facility (IRTF) at Maunakea Observatory in Hawaii. As in the case of our previous analyses, maps of H2O2 have been obtained using line depth ratios of weak transitions of H2O2 divided by a weak CO2 line. The H2O2 map of April 2016 shows a strong dichotomy between the Northern and Southern hemispheres, as predicted by the photochemical model developed in the Mars Climate Database (Forget et al. 1999) and in the Global Environmental Multiscale model (Daerden et al. 2019). The second measurement in July 2018 was taken in the middle of the MY 34 global dust storm. H2O2 was not detected, with a disk-integrated 2-sigma upper limit of 10 ppbv, while both the MCD and the LEM models predicted a value above 20 ppbv that was actually observed by TEXES in 2003 in the absence of dust storm (Encrenaz et al., 2004). This July 2018 depletion is probably the result of the high dust content in the atmosphere at the time of our observations, which led to a decrease of the water vapor column density in the relevant altitude range, as observed by PFS on Mars Express during this period (Giuranna and Wolkenberg, 2019). GCM simulations using the GEM model show that the H2O depletion leads to a drop of H2O2 due to the depletion of HO2 radicals whose self-recombination gives rise to H2O2. Our data provide new constraints to the photochemical modelling of H2O2 in the presence of a high dust content. In parallel, we have reprocessed the whole TEXES dataset of H2O2 measurements using the latest version of the GEISA database (2015). We have recently found that there is a significant difference in the H2O2 line strengths between the 2003 and 2015 versions of GEISA. Therefore, all H2O2 mixing ratios up to 2014 from TEXES measurements have been reduced by a factor of about 1.75. As a consequence, in four cases (Ls around 80°, 100°, 150° and 209°), H2O2 abundances show contradictory values between different Martian years, while, at Ls = 209°, the cause seems to be the increased dust content associated with the global dust storm. The inter-annual variability in the three other cases remains unexplained at this time. [ABSTRACT FROM AUTHOR]

The ExoMars Trace Gas Orbiter (TGO) is a joint ESA-Roscosmos mission to Mars that waslaunched in March 2016. The nominal science phase with regular measurement could onlystart 2 years later, that is in late spring 2018. The Atmospheric Chemistry Suite (ACS) is a setof three spectrometers (NIR, MIR, and TIRVIM), capable of sounding Mars&#x2019; atmosphere innadir and solar occultation modes. The design of the middle infrared (MIR) channel wasoptimized to overachieve the primary science goal of the TGO mission by accomplishing themost sensitive measurements ever of the trace gases present in the Martian atmosphere. Thehigh aperture of the spectrometer, the ultra-high spectral resolution, and a fast onboard frameprocessing ensure quality meeting the highest standards. Besides methane survey, ACSMIR is capable of investigating many other minor species: CH2O, HCl, HO2, andothers. Preliminary results and status of this work will be presented in the talk. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Suite (ACS) began regular science operations in April 2018 onboard the ExoMars Trace Gas Orbiter (TGO). The mid-infrared channel (MIR) of theinstrument is a cross-dispersion echelle spectrometer dedicated to solar occultationmeasurements in the 2.3–4.3 μm wavelength range [1]. The experiment demonstrates thesignal-to-noise ratio SNR up to ∼3000 with the instrumental resolving power of∼30,000. Each occultation session covers a spectral interval with one or a few CO2absorption bands appropriate for the atmospheric temperature retrieval. We usetemperature independent set of lines (e.g. at 3.13-3.15 μm or around 4 μm) andthe hydrostatic equilibrium condition to determine temperature profile from theretrieved CO2 local densities. Another method, using low state energies of rotationalCO2 transitions, is also tested since their lines are well resolved individually by theinstrument. In this paper, we present results from the first year of ACS MIR temperature profileretrievals in the solar occultation mode. Statistics of observations provides almost regulartime coverage including two phases of the global dust storm in 2018, started around June 1st(LS ≈180) and October 1st (LS ≈270). Temperature variability before and during the stormis studied at altitudes from 3-30 km up to 100 km. ACKNOWLEDGEMENTS ExoMars is the space mission of ESA and Roscosmos. The ACS experiment is led by IKISpace Research Institute in Moscow. The project acknowledges funding by Roscosmos andCNES. Science operations of ACS are funded by Roscosmos and ESA. Science support inIKI is funded by the Russian Government Grant #14.W03.31.0017. REFERENCES [1] Korablev O., Montmessin F., and the ACS Team. The Atmospheric Chemistry Suite(ACS) of three tpectrometers for the ExoMars 2016 Trace Gas Orbiter. Space Sci. Rev.,214:7, 2018. (DOI 10.1007/s11214-017-0437-6). [ABSTRACT FROM AUTHOR]

The ExoMars Trace Gas Orbiter (TGO), a collaborative project between the European Space Agency and Roscosmos, was successfully inserted into Mars orbit on 19 October 2016, and reached its final science orbit on 7 April 2018. TGO began taking observations as part of commissioning operations in March 2018.At the Laboratoire de Météorologie Dynamique (LMD) we are responsible for data assimilation of observations from the Atmospheric Chemistry Suite (ACS) thermal infrared instrument (TIRVIM) on board TGO. This instrument measures vertical profiles of temperature as well as dust and water ice integrated content, at various local times, latitudes and seasons.Here we report on assimilation of the first six weeks of TIRVIM observations into the LMD Mars General Circulation Model (GCM), using the Local Ensemble Transform Kalman Filter (LETKF) technique. The LETKF is an ensemble-based assimilation scheme where we typically use 16 ensemble members and multiplicative inflation to adjust the background ensemble error covariance. The assimilation focuses on atmospheric temperatures retrieved from nadir thermal emission spectra taken between 2018 March 13 and 2018 April 28. These have been calibrated and then retrieved using a line-by-line radiative transfer model. The observations cover various local times of day with full coverage in longitude every 7-10 days, over +/- 75 degree latitude, with vertical coverage between 5-45 km altitude.We shall report on the differences between the assimilation and a free-running model, particularly at local times of day that have not been observed prior to TGO. We shall also report on progress combining assimilation of ACS observations with profiles from Mars Climate Sounder on board NASA's Mars Reconnaissance Orbiter, to fill in anticipated gaps in the ACS observational record and to sample the local time of day more fully. [ABSTRACT FROM AUTHOR]

The ExoMars Trace Gas Orbiter (TGO), a mission by ESA and Roscosmos started its operational scientific phase in March 2018. The Atmospheric Chemistry Suite (ACS) is a set of three spectrometers (NIR, MIR, and TIRVIM) designed to observe the Martian atmosphere in solar occultation, nadir and limb geometry. The thermal infrared channel — TIRVIM is a Fourier-transform spectrometer covering the spectral range of 1.7–17 μm with a spectral resolution of 0.8 cm−1 for nadir observations. In nadir operation mode, the primary goal of TIRVIM is the long-term monitoring of atmospheric temperature and aerosol (dust and ice clouds) state from the surface up to approximately 60 km. In June 2018 a global dust storm enshrouded Mars for more than a month. We present the evolution of the thermal structure, dust content and optical properties during this period. AcknowledgementsExoMars is the space mission of ESA and Roscosmos. The ACS experiment is led by IKI Space Research Institute in Moscow. The project acknowledges funding by Roscosmos and CNES. Science operations of ACS are funded by Roscosmos and ESA. [ABSTRACT FROM AUTHOR]

The molecular oxygen is the minor constituent of the Martian atmosphere with the meanmixing ratio of (1.56 ± 0.06) 10−3. As it is a long-lived incondensable species(with the lifetime ∼60 years) the O2 mixing ratio should have latitudinal variationsinduced by condensation and sublimation of CO2 from the polar caps that result inenrichment and depletion and seasonal variations following the total CO2 amount inthe atmosphere. The O2 column-averaged mixing ratio was provided by severalground-based observations as well as by Herschel orbiting observatory. Now the highprecision measurements of the O2 mean surface mixing ratio were obtained by thequadrupole mass spectrometer as a part of Mars Science Laboratory at the Curiosityrover. The Atmospheric Chemistry Suite (ACS) is a set of three spectrometers (-NIR, -MIR, and-TIRVIM) intended to observe Mars atmosphere onboard the ESA-Roscosmos ExoMars2016 Trace Gas Orbiter (TGO) mission. The near infrared channel (NIR) is a compactspectrometer operating in the range of 0.7–1.7 μm with a resolving power of λ/Δλ ∼25,000. It is designed to operate in nadir and in solar occultation modes. A verticalprofiling of the O2 density based on 0.76 μm band is a unique feature of the ACSNIR science in occultation. No other instrument on a Mars orbiting platform beingsensitive to O2 from 10 to 60 km altitude range. Here we present the first results ofthe O2 density retrievals from the ACS/NIR solar occultations for the first yearof observations and the comparison with the LMD General Circulation model. [ABSTRACT FROM AUTHOR]

The Atmospheric Chemistry Suite (ACS) on board ESA-Roscosmos ExoMars Trace GasOrbiter started routine science operations in March 2018. The mid-infrared channel (MIR),operating in the 2.2-4.4 μm range, allows the detection of trace gases in the Martianatmosphere, as well as the simultaneous profiling of several species in solar occultationobservations. We report retrievals in the 2.51 – 2.64 μm spectral region which allow simultaneousmeasurement, for the first time, of vertical profiles of H216O, H218O, H217O and HD16O.The spectral region also includes CO2 spectral lines which allow temperature and pressureretrieval through the assumption of hydrostatic equilibrium. Monitoring of this spectral region with ACS-MIR will provide a better understanding ofthe isotopic fractionation of water vapour, its local and seasonal variability, and itsfractionation in condensation/evaporation processes. [ABSTRACT FROM AUTHOR]