T. Encrenaz, B. Bézard, T. Owen, S. Lebonnois, F. Lefèvre, T. Greathouse, M. Richter, J. Lacy, S. Atreya, A. S. Wong, and F. Forget. Infrared imaging spectroscopy of Mars: H 2O mapping and determination of CO 2 isotopic ratios. Icarus, 179:43-54, 2005. [ bib | DOI | ADS link ]
High-resolution infrared imaging spectroscopy of Mars has been achieved at the NASA Infrared Telescope Facility (IRTF) on June 19-21, 2003, using the Texas Echelon Cross Echelle Spectrograph (TEXES). The areocentric longitude was 206deg. Following the detection and mapping of hydrogen peroxide H 2O 2 [Encrenaz et al., 2004. Icarus 170, 424-429], we have derived, using the same data set, a map of the water vapor abundance. The results appear in good overall agreement with the TES results and with the predictions of the Global Circulation Model (GCM) developed at the Laboratory of Dynamical Meteorology (LMD), with a maximum abundance of water vapor of 31.5×10(179 pr-μm). We have searched for CH 4 over the martian disk, but were unable to detect it. Our upper limits are consistent with earlier reports on the methane abundance on Mars. Finally, we have obtained new measurements of CO 2 isotopic ratios in Mars. As compared to the terrestrial values, these values are: ( 18O/ 17O)[M/E] = 1.03 0.09; ( 13C/ 12C)[M/E] = 1.00 0.11. In conclusion, in contrast with the analysis of Krasnopolsky et al. [1996. Icarus 124, 553-568], we conclude that the derived martian isotopic ratios do not show evidence for a departure from their terrestrial values.
T. Encrenaz, R. Melchiorri, T. Fouchet, P. Drossart, E. Lellouch, B. Gondet, J.-P. Bibring, Y. Langevin, D. Titov, N. Ignatiev, and F. Forget. A mapping of martian water sublimation during early northern summer using OMEGA/Mars Express. Astronomy Astrophysics, 441:L9-L12, 2005. [ bib | DOI | ADS link ]
The OMEGA imaging spectrometer aboard Mars Express has been used to map the water vapor abundance over the martian surface, from the analysis of the 2.6 μm band of H2O. As a preliminary result of this study, we present water vapor maps in the northern hemisphere at the time of the northern polar cap sublimation (Ls = 94-112 deg). The maps show a mean H2O mixing ratio of about 2-3× 10-4 at a latitude of 40N, and in the range of 5 × 10-4-10-3 at 60N-80N latitudes. The corresponding mean H2O column densities are about 25 pr-μm at 40N and between 40 and 60 pr-μm at 60N-80N, with uncertainties of about 30 percent. Our results are in agreement with previous results by MAWD/Viking and TES/MGS for latitudes up to 60N, but seem to indicate lower values at high latitude. However they are still globally consistent in view of our error bars.
F. González-Galindo, M. A. López-Valverde, M. Angelats i Coll, and F. Forget. Extension of a Martian general circulation model to thermospheric altitudes: UV heating and photochemical models. Journal of Geophysical Research (Planets), 110:E09008, 2005. [ bib | DOI | ADS link ]
A fast method to incorporate the UV heating and the photochemistry of the neutral upper atmosphere of Mars into general circulation models (GCMs) is presented. On the basis of more detailed one-dimensional (1-D) models, the scheme we propose makes use of a division of the UV spectrum in 36 subintervals of 20 nm average width. Photoabsorption coefficients are computed allowing for overlapping and are tabulated as a function of suitable column abundances. The photochemistry proposed includes 12 compounds and uses the approximation of photochemical equilibrium for the three fastest species, OH, O(1D), and HO2. The behavior of the fast scheme is shown against detailed 1-D calculations. The resulting acceleration is about a factor 200 in the UV heating, while in the photochemistry it is about a factor 100 at 120 km and much larger below. The proposed scheme has already been implemented into the GCM developed at the Laboratoire de Météorologie Dynamique-CNRS in Paris (LMD), which therefore becomes the first single Martian GCM to cover the whole range of altitudes from the planet surface to the upper thermosphere. We present typical results of the Martian thermosphere obtained with the present scheme and the LMD-GCM, in order to illustrate its behavior and stability. In particular, we show the sensitivity of the Martian upper atmosphere's thermal structure to the local photochemistry. Comparisons with previous models are also presented, as first steps in an ongoing validation study, necessarily extensive for this kind of GCM, which will include more detailed comparisons with recent and future data from space missions.
H. M. Böttger, S. R. Lewis, P. L. Read, and F. Forget. The effects of the martian regolith on GCM water cycle simulations. Icarus, 177:174-189, 2005. [ bib | DOI | ADS link ]
This paper describes General Circulation Model (GCM) simulations of the martian water cycle focusing on the effects of an adsorbing regolith. We describe the 10-layer regolith model used in this study which has been adapted from the 1-D model developed by Zent, A.P., Haberle, R.M., Houben, H.C., Jakosky, B.M. [1993. A coupled subsurface-boundary layer model of water on Mars. J. Geophys. Res. 98 (E2), 3319-3337, February]. Even with a 30-min timestep and taking into account the effect of surface water ice, our fully implicit scheme compares well with the results obtained by Zent, A.P., Haberle, R.M., Houben, H.C., Jakosky, B.M. [1993. A coupled subsurface-boundary layer model of water on Mars. J. Geophys. Res. 98 (E2), 3319-3337, February]. This means, however, that the regolith is not able to reproduce the diurnal variations in column water vapour abundance of up to a factor of 2-3 as seen in some observations, with only about 10% of the atmospheric water vapour column exchanging with the subsurface on a daily basis. In 3-D simulations we find that the regolith adsorbs water preferentially in high latitudes. This is especially true in the northern hemisphere, where perennial subsurface water ice builds up poleward of 60deg N at depths which are comparable to the Odyssey observations. Much less ice forms in the southern high latitudes, which suggests that the water ice currently present in the martian subsurface is not stable under present conditions and is slowly subliming and being deposited in the northern hemisphere. When initialising the model with an Odyssey-like subsurface water ice distribution the model is capable of forcing the simulated water cycle from an arbitrary state close to the Mars Global Surveyor Thermal Emission Spectrometer observations. Without the actions of the adsorbing regolith the equilibrated water cycle is found to be a factor of 2-4 too wet. The process by which this occurs is by adsorption of water during northern hemisphere summer in northern mid and high latitudes where it remains locked in until northern spring when the seasonal CO 2 ice cap retreats. At this time the water diffuses out of the regolith in response to increased temperature and is returned to the residual water ice cap by eddie transport.
E. Millour, G. Labrosse, and E. Tric. Axisymmetric convective states of pure and binary liquids enclosed in a vertical cylinder and boundary conditions' influence thereupon. Physics of Fluids, 17(4):044102-044102, 2005. [ bib | DOI | ADS link ]
The high Rayleigh number (Ra) axisymmetric convection regimes of Pr =1 pure and (Le =0.1, Ψ =-0.2) binary liquids are numerically investigated and compared. The fluids are enclosed in a vertical cylinder of aspect ratio height/radius=2 and heated from below, with either no-slip or free-slip kinematic lateral boundary conditions. Branches of solutions and transitions between states that occur as Ra is varied up to O(105) are given, along with a description of the encountered bifurcations. When a free-slip condition is imposed along the circumference of the cell, pure fluid and binary liquid stationary flows are found to become identical at high Ra, an often reported feature. When the lateral boundary condition is set to no-slip, the high Ra steady flows of pure and binary liquid, although very similar, undergo different bifurcations. This is related with a locally quasiquiescent region present in both cases, the stability of which controls the flow regime in the whole fluid layer. A branch of resulting oscillatory states thus does not appear in the bifurcation diagram of the binary liquid.
S. Lebonnois. Benzene and aerosol production in Titan and Jupiter's atmospheres: a sensitivity study. Planetary and Space Science, 53:486-497, 2005. [ bib | DOI | ADS link ]
Benzene has recently been observed in the atmosphere of Jupiter, Saturn and also Titan. This compound is required as a precursor for larger aromatic species (PAHs) that may be part of aerosol particles. Several photochemical models have tried to reproduce the observed quantities of benzene in the atmospheres of Jupiter (both low- and high-latitudes regions), Saturn and Titan. In this present work, we have conducted a sensitivity study of benzene and PAHs formation, using similar photochemical schemes both for Titan and Jupiter (low-latitudes conditions). Two different photochemical schemes are used, for which the modeled composition fairly agrees with observational constraints, both for Jupiter and Titan. Some disagreements are specific to each atmospheric case, which may point to needed improvements, especially in kinetic data involved in the corresponding chemical cycles. The observed benzene mole fraction in Titan's stratosphere is reproduced by the model, but in the case of Jupiter, low-latitudes benzene abundance is only 3% of the observed column density, which may indicate a possible influence of latitudinal transport, since abundance of benzene is much higher in auroral regions. Though, the photochemical scheme of C6 compounds at temperature and pressure conditions of planetary atmospheres is still very uncertain. Several variations are therefore done on key reactions in benzene production. These variations show that benzene abundance is mainly sensitive to reactions that may affect the propargyl radical. The effect of aerosol production on hydrocarbons composition is also tested, as well as possible heterogenous recombination of atomic hydrogen in the case of Titan. PAHs are a major pathway for aerosol production in both models. The mass production profiles for aerosols are discussed for both Titan and Jupiter. Total production mass fluxes are roughly three times the one expected by observational constraints in both cases. Such comparative studies are useful to bring more constraints on photochemical models.
J. Urban, K. Dassas, F. Forget, and P. Ricaud. Retrieval of vertical constituents and temperature profiles from passive submillimeter wave limb observations of the Martian atmosphere: a feasibility study. Applied Optics, 44:2438-2455, 2005. [ bib | DOI | ADS link ]
The investigation of the Martian atmosphere is of key importance for an understanding of the planets present and past. Passive limb observations of thermal radiation at submillimeter wavelengths in the 320-350-GHz range by use of a state-of-the-art satellite receiver on a low Mars orbit allow important parameters such as the mixing ratios of H2O, HDO, 12CO, 13CO, O3, and H2O2 as well as the thermal profile to be retrieved with high precision and unprecedented vertical range and resolution, providing valuable information for better understanding of the planet's water cycle, atmospheric dynamics, and photochemistry. The feasibility of these kinds of measurement is demonstrated by means of model simulations based on realistic atmospheric, spectroscopic, and instrumental parameters. Temperature can be retrieved to ˜90 km with half-scale height vertical resolution from single-scan measurements of emission lines of the long-lived species 12CO and 13CO. The global water-vapor distribution can be measured even under dry or wet conditions with good vertical resolution from the surface to ˜45 km, and simultaneous observations of HDO allow useful information on the D/H ratio up to an altitude of ˜30 km to be derived. The sensitivity of the limb-sounding technique also permits information on the photochemically important minor species O3 and H2O2 to be obtained. It is shown that spectral averaging may improve precision, altitude range, and resolution of the retrieved profiles. Other frequency bands are explored, and the 435-465-GHz range is suggested as a possible alternative to the 320-350-GHz range.
J.-P. Bibring, Y. Langevin, A. Gendrin, B. Gondet, F. Poulet, M. Berthé, A. Soufflot, R. Arvidson, N. Mangold, J. Mustard, P. Drossart, OMEGA Team, S. Erard, O. Forni, M. Combes, T. Encrenaz, T. Fouchet, R. Merchiorri, G. Belluci, F. Altieri, V. Formisano, G. Bonello, F. Capaccioni, P. Cerroni, A. Coradini, S. Fonti, V. Kottsov, N. Ignatiev, V. Moroz, D. Titov, L. Zasova, M. Mangold, P. Pinet, S. Douté, B. Schmitt, C. Sotin, E. Hauber, H. Hoffmann, R. Jaumann, U. Keller, T. Duxbury, and F. Forget. Mars Surface Diversity as Revealed by the OMEGA/Mars Express Observations. Science, 307:1576-1581, 2005. [ bib | DOI | ADS link ]
The Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA) investigation, on board the European Space Agency Mars Express mission, is mapping the surface composition of Mars at a 0.3- to 5-kilometer resolution by means of visible-near-infrared hyperspectral reflectance imagery. The data acquired during the first 9 mineralogy, offering key insights into the evolution of Mars. OMEGA has identified and mapped mafic iron-bearing silicates of both the northern and southern crust, localized concentrations of hydrated phyllosilicates and sulfates but no carbonates, and ices and frosts with a water-ice composition of the north polar perennial cap, as for the south cap, covered by a thin carbon dioxide-ice veneer.
F. Montmessin, T. Fouchet, and F. Forget. Modeling the annual cycle of HDO in the Martian atmosphere. Journal of Geophysical Research (Planets), 110:E03006, 2005. [ bib | DOI | ADS link ]
We present the results of the first three-dimensional (3-D) simulation of the water isotope HDO in the Martian atmosphere. This deuterated isotope of water has long been used on both Earth and Mars as a proxy to understand the climatic evolutions of these planets. On Mars, the current enrichment in deuterium concentration in the atmosphere is believed to be indirect evidence of a wetter climate in the past. Due to its vapor pressure being lower than that of H2O, HDO gets fractionated at condensation and therefore concentrates in the Martian water ice clouds. Our study aims at understanding the latitudinal, vertical, and temporal variations of this species under current Martian climate. Our results indicate that the globally averaged D/H ratio in the Martian atmosphere should vary modestly with season, with changes on the order of 2%. Locally, however, this same ratio exhibits large annual changes (by a factor of 2) in the high-latitude regions. These fluctuations are controlled by the Polar Hood water ice clouds, within which HDO gets heavily fractionated. Due to the combined action of summer clouds above the north polar cap and to the cold-trapping effect of the south residual cap, the global atmospheric deuterium concentration is predicted to be more than 15% lower than the concentration in the north permanent cap ice. We thus extrapolate by suggesting that the “true” D/H ratio of Martian water may exceed 6.5 (wrt. SMOW), rather than the 5.6 inferred from atmospheric probing. The globally and annually averaged vertical distribution of HDO exhibits a mild decline with altitude, a result in significant contrast with previous 1-D studies. These results will help constrain more accurately the photochemical models aimed at understanding the observed low concentration of deuterium at high altitudes and thus the process of water escape to space.
M. Angelats i Coll, F. Forget, M. A. López-Valverde, and F. González-Galindo. The first Mars thermospheric general circulation model: The Martian atmosphere from the ground to 240 km. Geophysical Research Letters, 32:L04201, 2005. [ bib | DOI | ADS link ]
The Martian general circulation model (GCM) at the Laboratoire de Météorologie Dynamique (LMD) has been extended up to approximately 240 km and it is now the first GCM to fully simulate the Martian atmosphere from the ground up to the thermosphere. In this paper we summarize the processes that have been added and give a first simple study of the effects of parameterized orographic gravity waves on the zonal mean fields. This first study clearly emphasizes the coupling between the different atmospheric regions and notes the importance of having fully coupled models to simulate the atmosphere of Mars.
J.-L. Bertaux, F. Leblanc, S. Perrier, E. Quemerais, O. Korablev, E. Dimarellis, A. Reberac, F. Forget, P. C. Simon, S. A. Stern, and B. Sandel. Nightglow in the Upper Atmosphere of Mars and Implications for Atmospheric Transport. Science, 307:566-569, 2005. [ bib | DOI | ADS link ]
We detected light emissions in the nightside martian atmosphere with the SPICAM (spectroscopy for the investigation of the characteristics of the atmosphere of Mars) ultraviolet (UV) spectrometer on board the Mars Express. The UV spectrum of this nightglow is composed of hydrogen Lyman α emission (121.6 nanometers) and the γ and δ bands of nitric oxide (NO) (190 to 270 nanometers) produced when N and O atoms combine to produce the NO molecule. N and O atoms are produced by extreme UV photodissociation of O2, CO2, and N2 in the dayside upper atmosphere and transported to the night side. The NO emission is brightest in the winter south polar night because of continuous downward transport of air in this region at night during winter and because of freezing at ground level.
P. Rannou, S. Lebonnois, F. Hourdin, and D. Luz. Titan atmosphere database. Advances in Space Research, 36:2194-2198, 2005. [ bib | DOI | ADS link ]
We have developed in the last decade a two-dimensional version of the Titan global circulation model LMDZ. This model accounts for multiple coupling occuring on Titan between dynamics, haze, chemistry and radiative transfer. It was successful at explaining many observed features related to atmosphere state (wind, temperature), haze structure and chemical species distributions, recently, an important step in our knowledge about Titan has been done with Cassini and Huygens visits to Titan. In this context, we want to make the results of our model available for the scientific community which is involved in the study of Titan. Such a tool should be useful to give a global frame (spatial and time behaviour of physical quantities) for interpreting ground based telescope observations.
J.-L. Bertaux, O. Korablev, D. Fonteyn, S. Guibert, E. Chassefière, F. Lefèvre, E. Dimarellis, J. P. Dubois, A. Hauchecorne, M. Cabane, P. Rannou, A. C. Levasseur-Regourd, G. Cernogora, E. Quémerais, C. Hermans, G. Kockarts, C. Lippens, M. de Maziere, D. Moreau, C. Muller, E. Neefs, P. C. Simon, F. Forget, F. Hourdin, O. Talagrand, V. I. Moroz, A. Rodin, B. Sandel, and A. Stern. Global structure and composition of the martian atmosphere with SPICAM on Mars express. Advances in Space Research, 35:31-36, 2005. [ bib | DOI | ADS link ]
SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars (SPICAM) Light, a light-weight (4.7 kg) UV-IR instrument to be flown on Mars Express orbiter, is dedicated to the study of the atmosphere and ionosphere of Mars. A UV spectrometer (118-320 nm, resolution 0.8 nm) is dedicated to nadir viewing, limb viewing and vertical profiling by stellar and solar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H2O, aerosols, atmospheric vertical temperature structure and ionospheric studies. UV observations of the upper atmosphere will allow studies of the ionosphere through the emissions of CO, CO+, and CO2+, and its direct interaction with the solar wind. An IR spectrometer (1.0-1.7 μm, resolution 0.5-1.2 nm) is dedicated primarily to nadir measurements of H2O abundances simultaneously with ozone measured in the UV, and to vertical profiling during solar occultation of H2O, CO2, and aerosols. The SPICAM Light near-IR sensor employs a pioneering technology acousto-optical tunable filter (AOTF), leading to a compact and light design. Overall, SPICAM Light is an ideal candidate for future orbiter studies of Mars, after Mars Express, in order to study the interannual variability of martian atmospheric processes. The potential contribution to a Mars International Reference Atmosphere is clear.