arXiv subjects

Aurélien Stcherbinine

Publications and source records attributed to Aurélien Stcherbinine.

6 recordsLinked to original sources

arXiv2024

On the impact of the vertical structure of Martian water ice clouds on nadir atmospheric retrievals from simultaneous EMM/EXI and TGO/ACS-MIR observations

Retrieving the optical depth of the Martian clouds ($τ_\mathrm{cld}$) is a powerful way to monitor their spatial and temporal evolution. However, such retrievals from nadir imagery rely on several assumptions, including the vertical structure of the clouds in the atmosphere. Here we compare the results of cloud optical depth retrievals at 320 nm from the Emirates eXploration Imager (EXI) onboard the Emirates Mars Mission (EMM) "Hope" orbiter performed using a basic uniform cloud profile used in previous studies and using derived cloud profiles obtained from near-simultaneous Solar Occultation observations in the 3.1-3.4 $μ$m spectral range from the Middle-Infrared channel of the Atmospheric Chemistry Suite (ACS) instrument onboard the ESA Trace Gas Orbiter (TGO). We show that the latitudinal dependence of the cloud vertical profiles can have a strong impact on the nadir retrievals; neglecting it can lead to a significant underestimation of $τ_\mathrm{cld}$ in the polar regions (up to 25 % to 50 %, depending on the vertical distribution of the dust in the atmosphere) and to a lesser extent, to an overestimation of $τ_\mathrm{cld}$ around the equator. We also discuss the impact of a vertically-dependent particle size profile, as previous studies have shown the presence of very small water ice particles at the top of the clouds. From this analysis, we provide recommendations for the improvement of water ice cloud parameterization in radiative transfer algorithms in nadir atmospheric retrievals.

astro-ph.EP↗

arXiv2023

Diurnal and Seasonal Mapping of Martian Ices With EMIRS

Condensation and sublimation of ices at the surface of the planet is a key part of both the Martian H$_2$O and CO$_2$ cycles, either from a seasonal or diurnal aspect. While most of the ice is located within the polar caps, surface frost is known to be formed during nighttime down to equatorial latitudes. Here, we use data from the Emirates Mars Infrared Spectrometer (EMIRS) onboard the Emirates Mars Mission (EMM) to monitor the diurnal and seasonal evolution of the ices at the surface of Mars over almost one Martian year. The unique local time coverage provided by the instrument allows us to observe the apparition of equatorial CO$_2$ frost in the second half of the Martian night around the equinoxes, to its sublimation at sunrise.

astro-ph.EP↗

arXiv2023

A Two Martian Years Survey of Water Ice Clouds on Mars with ACS onboard TGO

The middle infrared (MIR) channel of the Atmospheric Chemistry Suite (ACS) instrument onboard the ExoMars Trace Gas Orbiter (TGO) ESA-Roscosmos mission has performed Solar occultation measurements of the Martian atmosphere in the 2.3-4.2 $μ$m spectral range since March 2018, which now covers two Martian Years (MY). We use the methodology previously developed for the study of the MY 34 Global Dust Storm (GDS) (Stcherbinine et al., 2020) to monitor the properties (effective radii, extinction, altitude) of the Martian water ice clouds over the first two Martian years covered by ACS-MIR. The observations encompass the period $L_s$ = 163° in MY 34 to $L_s$ = 181° in MY 36. We determine that the typical altitude of the clouds varies by 20 to 40 km between the summer and winter, with a maximum extension up to 80 km during summer in the midlatitudes. Similarly, we also note that for a limited temporal range, the altitude of the clouds also varies by 20 to 40 km between the polar regions and the midlatitudes. We also compare observations acquired during the MY 34 GDS to observations from the same period in MY 35, using that latter as a reference to characterize the effects of this GDS on the clouds' properties. In addition, we compare our retrievals with the predictions of the Mars Planetary Climate Model (PCM), which shows a reasonable agreement overall for the altitude of the clouds, although the model usually predicts lower altitudes for the top of the clouds.

astro-ph.EP↗

arXiv2021

Identification of a new spectral signature at 3 $μ$m over Martian northern high latitudes: implications for surface composition

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 $λ$ ${\geq}$ 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.

astro-ph.EP↗

arXiv2020

Martian water ice clouds during the 2018 global dust storm as observed by the ACS-MIR channel onboard the Trace Gas Orbiter

The Atmospheric Chemistry Suite (ACS) instrument onboard the ExoMars Trace Gas Orbiter (TGO) ESA-Roscosmos mission began science operations in March 2018. ACS Mid InfraRed (MIR) channel notably provides solar occultation observations of the martian atmosphere in the 2.3 - 4.2 $μ$m spectral range. Here we use these observations to characterize water ice clouds before and during the MY 34 Global Dust Storm (GDS). We developed a method to detect water ice clouds with mean particle size $\leq$ 2 $μ$m, and applied it to observations gathered between $L_s=165^\circ$ and $L_s=243^\circ$. We observe a shift in water ice clouds maximum altitudes from about 60 km before the GDS to above 90 km during the storm. These very high altitude, small-sized ($r_\mathrm{eff} \leq 0.3$ $μ$m) water ice clouds are more frequent during MY34 compared to non-GDS years at the same season. Particle size frequently decreases with altitude, both locally within a given profile and globally in the whole dataset. We observe that the maximum altitude at which a given size is observed can increase during the GDS by several tens of km for certain sizes. We notably notice some large water ice particles ($r_\mathrm{eff}\geq1.5$ $μ$m) at surprisingly high altitudes during the GDS (50 - 70 km). These results suggest that GDS can significantly impact the formation and properties of high altitude water ice clouds as compared to the usual perihelion dust activity.

astro-ph.EP↗

arXiv2019

Observational evidence for a dry dust-wind origin of Mars seasonal dark flows

Seasonal flows on warm slopes, or recurring slope lineae ("RSL"), have been presented as strong evidence for currently flowing water on Mars. This assumption was supported by a correlation between activity and warm temperatures, and by the spectral identification of hydrated salts. Here we first demonstrate that salts spectral identification is not robust, and that flow activity occurs on a wider range of seasons and slope orientations than previously thought, ruling out liquid water as a probable contributor. We then show that morphology, location and timing of flow activity is fully consistent with the removal and deposition of bright dust above darker underlying surfaces occurring notably in relation with seasonal dust storm activity. Mars recurring slope lineae are thus consistent with dust movements typical of present-day dry planet Mars.

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