Recent geological observations in the northern mid-latitudes of Mars show evidence for past glacial activity during the late Amazonian, similar to the integrated glacial landsystems in the Dry ...Valleys of Antarctica. The large accumulation of ice (many hundreds of meters) required to create the observed glacial deposits points to significant atmospheric precipitation, snow and ice accumulation, and glacial flow. In order to understand the climate scenario required for these conditions, we used the LMD (Laboratoire de Météorologie Dynamique) Mars GCM (General Circulation Model), which is able to reproduce the present-day water cycle, and to predict past deposition of ice consistent with geological observations in many cases. Prior to this analysis, however, significant mid-latitude glaciation had not been simulated by the model, run under a range of parameters.
In this analysis, we studied the response of the GCM to a wider range of orbital configurations and water ice reservoirs, and show that during periods of moderate obliquity (
ϵ
=
25–35°) and high dust opacity (
τ
dust
=
1.5–2.5), broad-scale glaciation in the northern mid-latitudes occurs if water ice deposited on the flanks of the Tharsis volcanoes at higher obliquity is available for sublimation. We find that high dust contents of the atmosphere increase its water vapor holding capacity, thereby moving the saturation region to the northern mid-latitudes. Precipitation events are then controlled by topographic forcing of stationary planetary waves and transient weather systems, producing surface ice distribution and amounts that are consistent with the geological record. Ice accumulation rates of ∼10
mm
yr
−1 lead to the formation of a 500–1000
m thick regional ice sheet that will produce glacial flow patterns consistent with the geological observations.
The vertical distribution of water vapor is key to the study of Mars' hydrological cycle. To date, it has been explored mainly through global climate models because of a lack of direct measurements. ...However, these models assume the absence of supersaturation in the atmosphere of Mars. Here, we report observations made using the SPICAM (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) instrument onboard Mars Express that provide evidence of the frequent presence of water vapor in excess of saturation, by an amount far surpassing that encountered in Earth's atmosphere. This result contradicts the widespread assumption that atmospheric water on Mars cannot exist in a supersaturated state, directly affecting our long-term representation of water transport, accumulation, escape, and chemistry on a global scale.
Water ice clouds play a key role in the radiative transfer of the Martian atmosphere, impacting its thermal structure, its circulation, and, in turn, the water cycle. Recent studies including the ...radiative effects of clouds in global climate models (GCMs) have found that the corresponding feedbacks amplify the model defaults. In particular, it prevents models with simple microphysics from reproducing even the basic characteristics of the water cycle. Within that context, we propose a new implementation of the water cycle in GCMs, including a detailed cloud microphysics taking into account nucleation on dust particles, ice particle growth, and scavenging of dust particles due to the condensation of ice. We implement these new methods in the Laboratoire de Météorologie Dynamique GCM and find satisfying agreement with the Thermal Emission Spectrometer observations of both water vapor and cloud opacities, with a significant improvement when compared to GCMs taking into account radiative effects of water ice clouds without this implementation. However, a lack of water vapor in the tropics after Ls = 180° is persistent in simulations compared to observations, as a consequence of aphelion cloud radiative effects strengthening the Hadley cell. Our improvements also allow us to explore questions raised by recent observations of the Martian atmosphere. Supersaturation above the hygropause is predicted in line with Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars observations. The model also suggests for the first time that the scavenging of dust by water ice clouds alone fails to fully account for the detached dust layers observed by the Mars Climate Sounder.
Key Points
Radiatively active clouds impact atmospheric water vapor and ice in a GCMCloud microphysics with dynamic nuclei is needed in GCMs
Aims.
The ExoMars Trace Gas Orbiter was sent to Mars in March 2016 to search for trace gases diagnostic of active geological or biogenic processes.
Methods.
We report the first observation of the ...spectral features of Martian ozone (O
3
) in the mid-infrared range using the Atmospheric Chemistry Suite Mid-InfaRed (MIR) channel, a cross-dispersion spectrometer operating in solar occultation mode with the finest spectral resolution of any remote sensing mission to Mars.
Results.
Observations of ozone were made at high northern latitudes (>65°N) prior to the onset of the 2018 global dust storm (L
s
= 163–193°). During this fast transition phase between summer and winter ozone distribution, the O
3
volume mixing ratio observed is 100–200 ppbv near 20 km. These amounts are consistent with past observations made at the edge of the southern polar vortex in the ultraviolet range. The observed spectral signature of ozone at 3000–3060 cm
−1
directly overlaps with the spectral range of the methane (CH
4
)
ν
3
vibration-rotation band, and it, along with a newly discovered CO
2
band in the same region, may interfere with measurements of methane abundance.
Context. Most exoplanets detected so far have atmospheric temperatures significantly higher than 300 K. Often close to their star, they receive an intense UV photons flux that triggers important ...photodissociation processes. The temperature dependency of vacuum ultraviolet (VUV) absorption cross sections are poorly known, leading to an undefined uncertainty in atmospheric models. Similarly, data measured at low temperatures similar to those of the high atmosphere of Mars, Venus, and Titan are often lacking. Aims. Our aim is to quantify the temperature dependency of the VUV absorption cross sections of important molecules in planetary atmospheres. We want to provide high-resolution data at temperatures prevailing in these media, and a simple parameterisation of the absorption in order to simplify its use in photochemical models. This study focuses on carbon dioxide (CO2). Methods. We performed experimental measurements of CO2 absorption cross sections with synchrotron radiation for the wavelength range (115–200 nm). For longer wavelengths (195–230 nm), we used a deuterium lamp and a 1.5 m Jobin-Yvon spectrometer. We used these data in our one-dimensional (1D) thermo-photochemical model in order to study their impact on the predicted atmospheric compositions. Results. The VUV absorption cross section of CO2 increases with the temperature. The absorption we measured at 150 K seems to be close to the absorption of CO2 in the fundamental ground state. The absorption cross section can be separated into two parts: a continuum and a fine structure superimposed on the continuum. The variation in the continuum of absorption can be represented by the sum of three Gaussian functions. Using data at high temperature in thermo-photochemical models significantly modifies the abundance and the photodissociation rates of many species in addition to CO2, such as methane and ammonia. These deviations have an impact on synthetic transmission spectra, leading to variations of up to 5 ppm. Conclusions. We present a full set of high-resolution (Δλ = 0.03 nm) absorption cross sections of CO2 from 115 to 230 nm for temperatures ranging from 150 to 800 K. A parameterisation allows us to calculate the continuum of absorption in this wavelength range. Extrapolation at higher temperature has not been validated experimentally and therefore should be used with caution. Similar studies on other major species are necessary to improve our understanding of planetary atmospheres.
Hydrogen chloride was discovered in the atmosphere of Mars for the first time during the global dust storm in Mars year (MY) 34 (July 2018) using the Atmospheric Chemistry Suite mid-infrared channel ...(ACS MIR) on the ExoMars Trace Gas Orbiter. The simultaneity of variations in dust and HCl, and a correlation between water vapour and HCl, led to the proposal of a novel surface-atmosphere coupling analogous to terrestrial HCl production in the troposphere from salt aerosols. After seasonal dust activity restarted in MY 35 (August 2020), we have been monitoring HCl activity to determine whether such a coupling was validated. Here we present a new technique for analysing the absorption features of trace gases close to the ACS MIR noise level and report that HCl mixing ratios are observed to rapidly increase in both hemispheres coincidentally with the onset of the MY 35 perihelion dust season. We present the temporal evolution of the vertical distribution of HCl (0.1–6 ppbv) and of dust activity in both hemispheres. We also report two observations of >2 ppbv HCl below 10 km in the northern hemisphere during the aphelion period.
We report a comprehensive study of Mars dayglow observations focusing on upper atmospheric structure and seasonal variability. We analyzed 744 vertical brightness profiles comprised of ∼109,300 ...spectra obtained with the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. The dayglow emission spectra show features similar to previous UV measurements at Mars. We find a significant drop in thermospheric scale height and temperature between LS = 218° and LS = 337–352°, attributed primarily to the decrease in solar activity and increase in heliocentric distance. We report the detection of a second, low‐altitude peak in the emission profile of OI 297.2 nm, confirmation of the prediction that the absorption of solar Lyman alpha emission is an important energy source there. The
CO2+ UV doublet peak intensity is well correlated with simultaneous observations of solar 17–22 nm irradiance at Mars.
Key Points
Significant drop in thermospheric temperature between two Martian seasons
Detection of second layer of OI 297.2 nm emission below 100 km
Strong correlation between observed mid‐UV dayglow and simultaneously measured EUV flux at Mars
•H2O mixing ratio and the cloud top altitudes were measured by SPICAV IR on VEx over 8.5 years.•The average H2O mixing ratio equals 5–7ppm at effective altitudes of 60–62km.•Two maxima in the ...latitudinal distribution of H2O were observed: near equator and near the pole.•A asymmetry of H2O longitudinal distribution has been observed in low latitudes.•No prominent long-term nor local time variations of H2O and the cloud tops were detected.
SPICAV VIS-IR spectrometer on-board the Venus Express mission measured the H2O abundance above Venus’ clouds in the 1.38µm band, and provided an estimation of the cloud top altitude based on CO2 bands in the range of 1.4–1.6µm. The H2O content and the cloud top altitude have been retrieved for the complete Venus Express dataset from 2006 to 2014 taking into account multiple scattering in the cloudy atmosphere. The cloud top altitude, corresponding to unit nadir aerosol optical depth at 1.48µm, varies from 68 to 73km at latitudes from 40ºS to 40ºN with an average of 70.2±0.8km assuming the aerosol scale height of 4km. In high northern latitudes, the cloud top decreases to 62–68km. The altitude of formation of water lines ranges from 59 to 66km. The H2O mixing ratio at low latitudes (20ºS-20ºN) is equal to 6.1±1.2ppm with variations from 4 to 11ppm and the effective altitude of 61.9±0.5km. Between 30º and 50º of latitude in both hemispheres, a local minimum was observed with a value of 5.4±1ppm corresponding to the effective altitude of 62.1±0.6km and variations from 3 to 8ppm. At high latitudes in both hemispheres, the water content varies from 4 to 12ppm with an average of 7.2±1.4ppm which corresponds to 60.6±0.5km. Observed variations of water vapor within a factor of 2-3 on the short timescale appreciably exceed individual measurement errors and could be explained as a real variation of the mixing ratio or/and possible variations of the cloud opacity within the clouds. The maximum of water at lower latitudes supports a possible convection and injection of water from lower atmospheric layers. The vertical gradient of water vapor inside the clouds explains well the increase of water near the poles correlating with the decrease of the cloud top altitude and the H2O effective altitude. On the contrary, the depletion of water in middle latitudes does not correlate with the H2O effective altitude and cannot be completely explained by the vertical gradient of water vapor within the clouds. Retrieved H2O mixing ratio is higher than those obtained in 2.56µm from VIRTIS-H data (Cottini et al., 2015 Planet. Space Sci., 113, 219–225 ) at altitudes of 68–70km which is well consistent with the lower altitudes of water mixing ratio from the 1.38µm band. Observations for different solar and emission angles allowed to constrain also the average vertical distribution of H2O mixing ratio in the clouds with 2ppm at 66km and 7–7.5ppm at 59–61km. The water vapor latitudinal-longitudinal distribution does not show any direct correlation with the cloud tops. Yet a strong asymmetry of H2O longitudinal distribution has been observed with a maximum of 7–7.5ppm from −120º to 30º of longitude and shifted to the southern hemisphere (20ºS-10ºN). To the east, the minimum is observed with values not in excess of 6ppm and over a wide range of longitudes from 30º to 160º. Bertaux et al. (2015) announced a correlation between the zonal wind pattern in the equatorial region and underlying topography of Aphrodite Terra as the result of stationary gravity waves produced at the ground level near the mountains. The water minimum corresponds to the Aphrodite Terra highlands and can be also associated with the influence of Venus topography. No prominent long-term on the time scale of 8.5 years nor local time variations of water vapor and the cloud top altitude were detected.
Surface conditions on Mars are currently cold and dry, with water ice unstable on the surface except near the poles. However, geologically recent glacierlike landforms have been identified in the ...tropics and the midlatitudes of Mars. The ice has been proposed to originate from either a subsurface reservoir or the atmosphere. We present high-resolution climate simulations performed with a model designed to simulate the present-day Mars water cycle but assuming a 45° obliquity as experienced by Mars a few million years ago. The model predicts ice accumulation in regions where glacier landforms are observed, on the western flanks of the great volcanoes and in the eastern Hellas region. This agreement points to an atmospheric origin for the ice and reveals how precipitation could have formed glaciers on Mars.
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