The SPICAM/MEX ultraviolet spectrometer probed the Martian atmosphere with the occultation method from 2004 until 2014. SPICAM/MEX performed both stellar and solar occultations during in total four ...Martian Years with good spatial and seasonal coverages. We have analyzed these occultations and performed a rigorous quality check of the retrievals to eliminate false detections. We present the observed features of the vertical distribution of Martian ozone, a key chemical species. Stellar occultations probe the nightside atmosphere, whereas solar occultations are acquired at the terminator (sunrise or sunset), enabling the study of the day–night transition of this photochemically active species. Comparison of the observations with a global climate model show a good overall agreement. However, quantitative differences are found in certain regions, possibly related to difficulties in correct modeling of the water cycle. Our dataset allows us to study certain particular features of Martian ozone. The low- and midlatitude ozone layer forming during northern spring is mapped in both hemispheres and its night–terminator variations are probed with the combination of stellar and solar occultations. The southern polar winter vortex shows hints of the well-known mid-altitude ozone layer already detected previously. During the northern polar spring, SPICAM observes the top of the lower atmosphere ozone layer above 10 km, showing O3 concentrations that the model reproduces quite well. SPICAM observations are in good agreement with previously published observations from other instruments.
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•We present a climatology of O3 vertical distribution from SPICAM/MEX UV occultations.•Solar and stellar occultations allow us to follow the terminator–night variation of ozone.•The observations detect the aphelion ozone layer at ∼35 km, and polar ozone in certain seasons.
THE MARTIAN ATMOSPHERIC BOUNDARY LAYER Petrosyan, A.; Galperin, B.; Larsen, S. E. ...
Reviews of geophysics (1985),
September 2011, Letnik:
49, Številka:
3
Journal Article
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The planetary boundary layer (PBL) represents the part of the atmosphere that is strongly influenced by the presence of the underlying surface and mediates the key interactions between the atmosphere ...and the surface. On Mars, this represents the lowest 10 km of the atmosphere during the daytime. This portion of the atmosphere is extremely important, both scientifically and operationally, because it is the region within which surface lander spacecraft must operate and also determines exchanges of heat, momentum, dust, water, and other tracers between surface and subsurface reservoirs and the free atmosphere. To date, this region of the atmosphere has been studied directly, by instrumented lander spacecraft, and from orbital remote sensing, though not to the extent that is necessary to fully constrain its character and behavior. Current data strongly suggest that as for the Earth's PBL, classical Monin‐Obukhov similarity theory applies reasonably well to the Martian PBL under most conditions, though with some intriguing differences relating to the lower atmospheric density at the Martian surface and the likely greater role of direct radiative heating of the atmosphere within the PBL itself. Most of the modeling techniques used for the PBL on Earth are also being applied to the Martian PBL, including novel uses of very high resolution large eddy simulation methods. We conclude with those aspects of the PBL that require new measurements in order to constrain models and discuss the extent to which anticipated missions to Mars in the near future will fulfill these requirements.
Launched on 2 June 2003 and arriving at Mars on 25 December 2003 after a 7-month interplanetary cruise, Mars Express was the European Space Agency’s first mission to arrive at another planet. After ...more than 20 years in orbit, the spacecraft and science payload remain in good health and the mission has become the second oldest operational planetary orbiter after Mars Odyssey.
This contribution summarizes the Mars Express mission operations, science planning and data archiving systems, processes, and teams that are necessary to run the mission, plan the scientific observations, and execute all necessary commands. It also describes the data download, the ground processing and distribution to the scientific community for the study and analysis of Mars sub-surface, surface, atmosphere, magnetosphere, and moons.
This manuscript also describes the main challenges throughout the history of the mission, including several potentially mission-ending anomalies. We summarize the evolution of the ground segment to provide new capabilities not envisaged before launch, whilst simultaneously maintaining or even increasing the quality and quantity of scientific data generated.
Ozone (O3) in the atmosphere of Mars is produced following the photolysis of CO2 and is readily destroyed by the hydrogen radicals (HOx) released by the photolysis and oxidation of water vapor. As a ...result, an anti‐correlation between ozone and water vapor is expected. We describe here the O3‐H2O relationship derived from 4 Martian years of simultaneous observations by the SPICAM spectrometer onboard the Mars Express spacecraft. A distinct anti‐correlation is found at high latitudes, where the O3 column varies roughly with the −0.6 power of the H2O column. The O3 and H2O columns are uncorrelated at low latitudes. To evaluate our quantitative understanding of the Martian photochemistry, the observed O3‐H2O relationship is then compared to that predicted by a global climate model with photochemistry. For identical model and observed abundances of H2O, the model underpredicts observed ozone by about a factor of 2 relative to SPICAM when using the currently recommended gas‐phase chemistry. Sensitivity studies employing low‐temperature CO2 absorption cross sections, or adjusted kinetics rates, do not solve this bias. Taking into account potential heterogeneous processes of HOx loss on clouds leads to a significant improvement, but only at high northern latitudes. More broadly, the modeled ozone deficits suggest that the HOx‐catalyzed photochemistry is too efficient in our simulations. This problem is consistent with the long‐standing underestimation of CO in Mars photochemical models, and may be related to similar difficulties in modeling O3 and HOx in the Earth's upper stratosphere and mesosphere.
Plain Language Summary
The thin ozone layer on Mars is produced when the solar ultraviolet light breaks the CO2 molecules that compose 95% of its atmosphere. Conversely, ozone on Mars is readily destroyed by the hydrogen species released by water vapor. An inverse relationship is therefore expected between the quantities of ozone and water vapor. Quantifying this relationship provides important insight into the hydrogen chemistry that stabilizes the composition of the Mars atmosphere. We describe here the ozone and water vapor measurements performed during 4 Martian years (7.5 Earth years) by the SPICAM instrument onboard the Mars Express spacecraft. We then attempt to reproduce these measurements with a Mars climate model with photochemistry. Although the model reproduces the inverse relationship observed between ozone and water vapor, the ozone amount is underestimated by about a factor of 2 in the simulations. The ozone deficit suggests that the destruction by hydrogen species is too strong when one uses the currently recommended reaction rates. This problem is consistent with the long‐standing underestimation in Mars models of carbon monoxide, also destroyed by hydrogen species, and can be related to similar difficulties in modeling ozone in the Earth's upper atmosphere.
Key Points
The relationship between the O3 and H2O columns on Mars is quantified from 4 Martian years of simultaneous measurements
The O3 and H2O columns are distinctly anti‐correlated at high latitudes but are uncorrelated at low latitudes
Model simulations using the observed amount of H2O and the currently recommended kinetics underpredict O3 by about a factor of 2
► We study H2O vertical profiles in Mars atmosphere with SPICAM solar occultations. ► The measured vertical distribution differs significantly from model predictions. ► Evolution of H2O and aerosols ...is strongly reactive to local perturbations. ► Connection between water vapor and aerosol profiles is tighter than expected. ► Water behavior in lower atmospheric layers is detached from the upper atmosphere.
The vertical distribution of water vapor is a very important diagnostic to determine the physical and chemical processes that drive the martian water cycle. Yet, very few direct measurements have been performed so far, and our knowledge of the H2O vertical distribution on Mars relies on General Circulation Models (GCMs). The study presented here follows for the first time the evolution of water vapor profile during a martian year. 120 profiles, obtained by the SPICAM spectrometer onboard Mars Express with the solar occultations technique, are retrieved. They cover the northern spring-summer season and the southern spring of Mars Year (MY) 29. The seasonal evolution of H2O mixing ratio vertical distribution reveals its strong dynamism, especially during southern spring. There are significant discrepancies with the predictions of the General Circulation Model developed at the Laboratoire de Météorologie Dynamique (LMD-GCM). The LMD-GCM underestimates the water vapor content in the middle atmosphere. The measured profiles also exhibit often abrupt temporal variations and a greater variety of shapes, with the frequent presence of detached layers. We believe that the model underestimates the strength of the coupling between water vapor and aerosols, whose slant optical depth profile is obtained by SPICAM simultaneously with H2O. The SPICAM measurements can be grouped according to the mutual behavior of the two profiles. Individual features are often related too. The presence of water supersaturation and of correlated aerosol–water detached layers highlights the role of water ice clouds as a favorable location for the dust–water coupling. The water vapor vertical distribution is more reactive than expected to regional perturbations, which can propagate rapidly through the atmosphere, create abrupt water vapor and aerosol upsurges and influence the large-scale vertical evolution of these two constituents. This phenomenon has been observed thrice during MY29. The martian annual water cycle revealed by the SPICAM profiles exhibits a different behavior with respect to nadir observations. This result suggests a generally weak connection between the upper atmosphere and the lower atmospheric layers, to whom the nadir measurements are most sensitive and that are not resolved by SPICAM occultations, and hints at a significant influence of surface-atmosphere interactions on the water cycle.
Rapid variations of pressure, temperature and illumination at the day–night terminator have the potential to cause asymmetries in the abundance distribution of the atmosphere constituents along the ...line of sight (LOS) of a solar occultation experiment. Ozone, in particular, displays steep density gradients across the terminator of Mars due to photolysis. Nowadays, most of the retrieval algorithms for solar and stellar occultations rely on the assumption of a spherically symmetrical atmosphere. However, photochemically induced variations near sunrise/sunset conditions need to be taken into account in the retrieval technique in order to prevent inaccuracies.
We investigated the impact of gradients along the LOS of the solar occultation experiment SPICAM/Mars Express for the retrieval of ozone under sunrise/sunset conditions. In order to test the impact of different gradients, we selected four occultations at sunrise and at sunset each. Sunset occultations are located near the equator, while sunrise observations are situated at high latitudes in the South, because of the geometry of the orbit.
We used the diurnal variations in the ozone concentration obtained from a three-dimensional General Circulation Model (GEM-Mars) together with an adapted radiative transfer code (ASIMUT). The General Circulation Model (GCM) suggests that ozone variations strongly depend on latitude, altitude, and season. As shown by the model, near the equator and below 25 km, ozone changes only slightly with local time. Around 45 km, the density changes by several orders of magnitude across the terminator. At high latitudes in the South, during northern winter time, ozone variations at the terminator are negligible.
The impact of gradients on ozone retrievals is strongly related to the local atmospheric structure as predicted by the GCM. Sunset ozone retrievals are smaller than retrievals obtained assuming a spherically symmetrical atmosphere, with a maximum change of about 20%. At sunrise, the impact of gradients on the retrievals is negligible. This behavior can be explained by the specific geometry of sunrise observations, all situated at high latitudes in the South.
•We analyzed the impact of gradients along the LOS of a solar occultation experiment.•We focused on the retrieval of ozone using observations acquired by SPICAM/MEx.•We implemented a radiative transfer code (ASIMUT) to take into account gradients.•We used the diurnal variations in ozone concentration obtained from a GCM (GEM-Mars).•The impact of gradients on retrievals is strongly related to the GCM model results.
Many boundary layer processes simulated within a Mars General Circulation Model (MGCM), including the description of the processes controlling dust rising from the Martian surface, are highly ...sensitive to the aerodynamic roughness length z0. On the basis of rock‐size frequency distributions inferred from different Martian landing sites and Earth analog sites, we have first established that lognormal‐modeled rock‐size frequency distributions are able to reproduce correctly the observed Martian rock populations. We have validated the hypothesis that the rock abundance ζ of a given area could be estimated at a first order from its thermophysical properties, namely its thermal inertia I and its albedo α. We have demonstrated the possibility of using rock abundance ζ to estimate the roughness density λ on Mars and to retrieve subsequently the aerodynamic roughness length by using semi‐empirical relationships based on terrestrial wind‐tunnel and field measurements. By combining our methodology with remote sensing measurements of the Thermal Emission Spectrometer aboard Mars Global Surveyor, we have derived a global map of the aeolian aerodynamic roughness length with a 1/8° × 1/8° resolution over the entire Martian surface. Contrary to what is often assumed, the Martian aeolian aerodynamic roughness length is spatially highly heterogeneous. At the fullest resolution, the Martian aerodynamic roughness length varies from 10−3 cm to 2.33 cm. About 84% of the Martian surface seems to be characterized by an aeolian aerodynamic roughness length value lower than 1 cm, the spatially uniform value that most of the MGCMs simulations have assumed recently. Since the aerodynamic roughness length z0 is a key parameter in deriving the erosion threshold wind velocities, we anticipate a significant impact of our findings on the efficiencies for lifting dust in future MGCMs.
Key Points
Extension of the Martian rock abundance data poleward
Validation of modeled rock size‐frequency distributions with ground‐truth data
Consistent and methodical mapping of the aerodynamic roughness length on Mars
•Results are presented from the Mars Express SPICAM instrument, which is a dual UV-IR instrument.•The presented dataset encompasses 10 terrestrial years of observation.•This climatology is unique by ...its temporal coverage and its vertical exploration of the Martian atmosphere.•Combined analysis of several key climate parameters is enabled.•Results reveal a coupling between the lower and the upper atmosphere faster than expected.
The SPICAM experiment onboard Mars Express has accumulated during the last decade a wealth of observations that has permitted a detailed characterization of the atmospheric composition and activity from the near-surface up to above the exosphere. The SPICAM climatology is one of the longest assembled to date by an instrument in orbit around Mars, offering the opportunity to study the fate of major volatile species in the Martian atmosphere over a multi-(Mars)year timeframe. With his dual ultraviolet (UV)-near Infrared channels, SPICAM observes spectral ranges encompassing signatures created by a variety atmospheric gases, from major (CO2) to trace species (H2O, O3). Here, we present a synthesis of the observations collected for water vapor, ozone, clouds and dust, carbon dioxide, exospheric hydrogen and airglows. The assembled climatology covers the MY 27–MY 31 period. However, the monitoring of UV-derived species was interrupted at the end of 2014 (MY30) due to failure of the UV channel. A SO2 detection attempt was undertaken, but proved unsuccessful from regional to global scales (with upper limit greater than already published ones). One particular conclusion that stands out from this overview work concerns the way the Martian atmosphere organizes an efficient mass transfer between the lower and the upper atmospheric reservoirs. This highway to space, as we name it, is best illustrated by water and hydrogen, both species having been monitored by SPICAM in their respective atmospheric reservoir. Coupling between the two appear to occur on seasonal timescales, much shorter than theoretical predictions.
Meteoric Metal Chemistry in the Martian Atmosphere Plane, J. M. C.; Carrillo‐Sanchez, J. D.; Mangan, T. P. ...
Journal of geophysical research. Planets,
March 2018, Letnik:
123, Številka:
3
Journal Article
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Recent measurements by the Imaging Ultraviolet Spectrograph (IUVS) instrument on NASA's Mars Atmosphere and Volatile EvolutioN mission show that a persistent layer of Mg+ ions occurs around 90 km in ...the Martian atmosphere but that neutral Mg atoms are not detectable. These observations can be satisfactorily modeled with a global meteoric ablation rate of 0.06 t sol−1, out of a cosmic dust input of 2.7 ± 1.6 t sol−1. The absence of detectable Mg at 90 km requires that at least 50% of the ablating Mg atoms ionize through hyperthermal collisions with CO2 molecules. Dissociative recombination of MgO+.(CO2)n cluster ions with electrons to produce MgCO3 directly, rather than MgO, also avoids a buildup of Mg to detectable levels. The meteoric injection rate of Mg, Fe, and other metals—constrained by the IUVS measurements—enables the production rate of metal carbonate molecules (principally MgCO3 and FeCO3) to be determined. These molecules have very large electric dipole moments (11.6 and 9.2 Debye, respectively) and thus form clusters with up to six H2O molecules at temperatures below 150 K. These clusters should then coagulate efficiently, building up metal carbonate‐rich ice particles which can act as nucleating particles for the formation of CO2‐ice clouds. Observable mesospheric clouds are predicted to occur between 65 and 80 km at temperatures below 95 K and above 85 km at temperatures about 5 K colder.
Plain Language Summary
When interplanetary dust particles enter a planetary atmosphere, collisions with air molecules cause heating and evaporation, a process termed meteoric ablation. This results in the continuous injection of metal atoms and ions into the planet's atmosphere. In the case of Earth, layers of metals such as Na and Fe have been observed for over 40 years. However, only very recently has a metallic layer been observed around another planet: a spectrometer on NASA's MAVEN spacecraft has detected a layer of Mg+ ions around 95 km. The present study explores the unusual chemistry of metallic ions in a CO2 atmosphere, and then develops a model of magnesium chemistry to explain the observed layer of Mg+ and the surprising absence of a detectable Mg layer. The model predicts that metals like Mg and Fe form carbonates, which readily condense water to form “dirty” ice particles at the low temperatures of the Mars upper atmosphere. These particles provide the seeds on which CO2 can condense at temperatures below −180°C, thus producing the clouds of CO2‐ice particles that have been observed by rovers on the surface of the planet and from orbiting spacecraft.
Key Points
A meteoric input function for Mars is generated by combining a cosmic dust input of ~3 tonnes sol−1 with a chemical ablation model
MAVEN/IUVS observations of Mg+, and a small upper limit for Mg, suggest that around 50% of Mg atoms ionize directly after ablation
MgCO3 and FeCO3 form stable H2O clusters which coagulate to metal‐rich ice particles, likely nuclei for clouds in the Martian mesosphere
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