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2013 .

(6 publications)

K. E. Scanlon, J. W. Head, J.-B. Madeleine, R. D. Wordsworth, and F. Forget. Orographic precipitation in valley network headwaters: Constraints on the ancient Martian atmosphere. Geophysical Research Letters, 40:4182-4187, August 2013. [ bib | DOI | ADS link ]

We examine the Martian valley networks in the framework of topographic influences on precipitation. We use an analytical model and the Laboratoire de Météorologie Dynamique (LMD) early Mars global circulation model (GCM) to explore the local-scale distribution of orographically forced precipitation as a function of atmospheric pressure. In simulations with 500 mbar and 1 bar CO2 atmospheres, orographic lifting results in enhanced snowfall upslope of the observed valley network tributaries. Our framework also suggests that a 2 bar atmosphere cannot create the observed valley pattern at the highest-relief valley network, Warrego Valles. As in previous work, the GCM does not generate temperatures warm enough for rain or significant snowmelt in the highlands with CO2 greenhouse warming alone. Thus while transient periods of unusual warming are still required to melt the deposits and carve the valleys, our model predicts snow deposition in the correct locations.

R. T. Clancy, B. J. Sandor, M. J. Wolff, M. D. Smith, F. LefèVre, J.-B. Madeleine, F. Forget, S. L. Murchie, F. P. Seelos, K. D. Seelos, H. Nair, A. D. Toigo, D. Humm, D. M. Kass, A. KleinböHl, and N. Heavens. Correction to ”Extensive MRO CRISM observations of 1.27 m O2 airglow in Mars polar night and their comparison to MRO MCS temperature profiles and LMD GCM simulations”. Journal of Geophysical Research (Planets), 118:1148-1154, May 2013. [ bib | DOI | ADS link ]

A. Spiga, J. Faure, J.-B. Madeleine, A. Määttänen, and F. Forget. Rocket dust storms and detached dust layers in the Martian atmosphere. Journal of Geophysical Research (Planets), 118:746-767, April 2013. [ bib | DOI | arXiv | ADS link ]

Airborne dust is the main climatic agent in the Martian environment. Local dust storms play a key role in the dust cycle; yet their life cycle is poorly known. Here we use mesoscale modeling that includes the transport of radiatively active dust to predict the evolution of a local dust storm monitored by OMEGA on board Mars Express. We show that the evolution of this dust storm is governed by deep convective motions. The supply of convective energy is provided by the absorption of incoming sunlight by dust particles, rather than by latent heating as in moist convection on Earth. We propose to use the terminology ”rocket dust storm,” or conio-cumulonimbus, to describe those storms in which rapid and efficient vertical transport takes place, injecting dust particles at high altitudes in the Martian troposphere (30-50 km). Combined to horizontal transport by large-scale winds, rocket dust storms produce detached layers of dust reminiscent of those observed with Mars Global Surveyor and Mars Reconnaissance Orbiter. Since nighttime sedimentation is less efficient than daytime convective transport, and the detached dust layers can convect during the daytime, these layers can be stable for several days. The peak activity of rocket dust storms is expected in low-latitude regions at clear seasons (late northern winter to late northern summer), which accounts for the high-altitude tropical dust maxima unveiled by Mars Climate Sounder. Dust-driven deep convection has strong implications for the Martian dust cycle, thermal structure, atmospheric dynamics, cloud microphysics, chemistry, and robotic and human exploration.

L. Kerber, F. Forget, J.-B. Madeleine, R. Wordsworth, J. W. Head, and L. Wilson. The effect of atmospheric pressure on the dispersal of pyroclasts from martian volcanoes. Icarus, 223:149-156, March 2013. [ bib | DOI | ADS link ]

A planetary global circulation model developed by the Laboratoire de Météorologie Dynamique (LMD) was used to simulate explosive eruptions of ancient martian volcanoes into paleo-atmospheres with higher atmospheric pressures than that of present-day Mars. Atmospheric pressures in the model were varied between 50 mbar and 2 bars. In this way it was possible to investigate the sensitivity of the volcanic plume dispersal model to atmospheric pressure. It was determined that the model has a sensitivity to pressure that is similar to its sensitivity to other atmospheric parameters such as planetary obliquity and season of eruption. Higher pressure atmospheres allow volcanic plumes to convect to higher levels, meaning that volcanic pyroclasts have further to fall through the atmosphere. Changes in atmospheric circulation due to pressure cause pyroclasts to be dispersed in narrower latitudinal bands compared with pyroclasts in a modern atmosphere. Atmospheric winds are generally slower under higher pressure regimes; however, the final distance traveled by the pyroclasts depends greatly on the location of the volcano and can either increase or decrease with pressure. The directionality of the pyroclast transport, however, remains dominantly east or west along lines of latitude. Augmentation of the atmospheric pressure improves the fit between possible ash sources Arsia and Pavonis Mons and the Medusae Fossae Formation, a hypothesized ash deposit.

F. Forget, R. Wordsworth, E. Millour, J.-B. Madeleine, L. Kerber, J. Leconte, E. Marcq, and R. M. Haberle. 3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds. Icarus, 222:81-99, January 2013. [ bib | DOI | arXiv | ADS link ]

On the basis of geological evidence, it is often stated that the early martian climate was warm enough for liquid water to flow on the surface thanks to the greenhouse effect of a thick atmosphere. We present 3D global climate simulations of the early martian climate performed assuming a faint young Sun and a CO2 atmosphere with surface pressure between 0.1 and 7 bars. The model includes a detailed radiative transfer model using revised CO2 gas collision induced absorption properties, and a parameterisation of the CO2 ice cloud microphysical and radiative properties. A wide range of possible climates is explored using various values of obliquities, orbital parameters, cloud microphysic parameters, atmospheric dust loading, and surface properties. Unlike on present day Mars, for pressures higher than a fraction of a bar, surface temperatures vary with altitude because of the adiabatic cooling and warming of the atmosphere when it moves vertically. In most simulations, CO2 ice clouds cover a major part of the planet. Previous studies had suggested that they could have warmed the planet thanks to their scattering greenhouse effect. However, even assuming parameters that maximize this effect, it does not exceed +15 K. Combined with the revised CO2 spectroscopy and the impact of surface CO2 ice on the planetary albedo, we find that a CO2 atmosphere could not have raised the annual mean temperature above 0 degC anywhere on the planet. The collapse of the atmosphere into permanent CO2 ice caps is predicted for pressures higher than 3 bar, or conversely at pressure lower than 1 bar if the obliquity is low enough. Summertime diurnal mean surface temperatures above 0 degC (a condition which could have allowed rivers and lakes to form) are predicted for obliquity larger than 40deg at high latitudes but not in locations where most valley networks or layered sedimentary units are observed. In the absence of other warming mechanisms, our climate model results are thus consistent with a cold early Mars scenario in which nonclimatic mechanisms must occur to explain the evidence for liquid water. In a companion paper by Wordsworth et al. we simulate the hydrological cycle on such a planet and discuss how this could have happened in more detail.

R. Wordsworth, F. Forget, E. Millour, J. W. Head, J.-B. Madeleine, and B. Charnay. Global modelling of the early martian climate under a denser CO2 atmosphere: Water cycle and ice evolution. Icarus, 222:1-19, January 2013. [ bib | DOI | arXiv | ADS link ]

We discuss 3D global simulations of the early martian climate that we have performed assuming a faint young Sun and denser CO2 atmosphere. We include a self-consistent representation of the water cycle, with atmosphere-surface interactions, atmospheric transport, and the radiative effects of CO2 and H2O gas and clouds taken into account. We find that for atmospheric pressures greater than a fraction of a bar, the adiabatic cooling effect causes temperatures in the southern highland valley network regions to fall significantly below the global average. Long-term climate evolution simulations indicate that in these circumstances, water ice is transported to the highlands from low-lying regions for a wide range of orbital obliquities, regardless of the extent of the Tharsis bulge. In addition, an extended water ice cap forms on the southern pole, approximately corresponding to the location of the Noachian/Hesperian era Dorsa Argentea Formation. Even for a multiple-bar CO2 atmosphere, conditions are too cold to allow long-term surface liquid water. Limited melting occurs on warm summer days in some locations, but only for surface albedo and thermal inertia conditions that may be unrealistic for water ice. Nonetheless, meteorite impacts and volcanism could potentially cause intense episodic melting under such conditions. Because ice migration to higher altitudes is a robust mechanism for recharging highland water sources after such events, we suggest that this globally sub-zero, 'icy highlands' scenario for the late Noachian climate may be sufficient to explain most of the fluvial geology without the need to invoke additional long-term warming mechanisms or an early warm, wet Mars.

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