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Francois Forget - One of the best experts on this subject based on the ideXlab platform.
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retrieval of the water Ice column and physical properties of water Ice Clouds in the martian atmosphere using the omega imaging spectrometer
Icarus, 2021Co-Authors: Kevin Olsen, Francois Forget, Jeanbaptiste Madeleine, A Szantai, Joachim Audouard, A Geminale, F Altieri, G Bellucci, F Oliva, L MontaboneAbstract:Abstract Using spectral images recorded by the OMEGA instrument on Mars Express (Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activite), we are able to derive physical properties of aerosols in water-Ice Clouds on Mars for a distribution of pixels over an observed cloud formation. These properties, mean effective radius, reff, and optical depth (at 0.67 μm), τi, were used to estimate the water Ice-column (WIC), and we found an empirical relationship between the WIC and an Ice cloud index (ICI). The overall mean of retrieved reff is ∼2.2 μm, with a standard deviation of 0.8 μm, and cloud formations with reff between 4.4 and 5.4 μm are observed. The optical depth varies between 0.2 and 2.0. The OMEGA spectra are primarily sensitive to water Ice mass due to absorption, and we find that the ICI, very easy to compute, is a good proxy for the mass of the water-Ice column (WIC) along the optical line of sight. Our retrieval of physical properties is limited in time (to before 2010) by the exhaustion of coolant for one of the OMEGA channels, and in space (to equatorial observations between 140∘W and 90∘E) by the availability of surface albedo measurements. However, we used the ICI to compute WIC values for the entire OMEGA data set, which has near-global coverage for Mars years 26–32, and we present a climatology of the WIC derived from the OMEGA data, which features enhancements on the order of 1.2–1.6 pr. μm over the aphelion cloud belt, and 1.5–2.5 pr. μm over the polar hoods. The data set analyzed is for observations between 140°W and 90°E, and between 35∘S and 35∘N. No restriction is placed on season, but the majority of cloudy observations were during the aphelion period from Ls 35∘ to 135∘. This work was motivated by the ability of the OMEGA instrument to observe the distribution of water-Ice cloud physical properties, and by the availability of new a priori data sets, especially multi-spectral, aerosol-free surface albedo retrieved from a subset of the OMEGA data featuring a cloud-free sky. The main limitations of the retrieval algorithm are linked to the uncertainties on surface albedo, the dust opacity, and the quantity of water-Ice suspended in the atmosphere, which can lead to spectral fits with lower accuracy or unrealistic results. We present distributions of each retrieved parameter, goodness of fit, ICI, and cloud mass, and our investigation of relationships between each parameter. Our approach was to maximize the amount of data analyzed, apply stringent data quality cuts and take a statistical approach to interpretation.
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snow precipitation on mars driven by cloud induced night time convection
Nature Geoscience, 2017Co-Authors: Aymeric Spiga, Francois Forget, T Navarro, Ehouarn Millour, D P Hinson, J B Madeleine, Franck MontmessinAbstract:Although it contains less water vapour than Earth’s atmosphere, the Martian atmosphere hosts Clouds. These Clouds, composed of water-Ice particles, influence the global transport of water vapour and the seasonal variations of Ice deposits. However, the influence of water-Ice Clouds on local weather is unclear: it is thought that Martian Clouds are devoid of moist convective motions, and snow precipitation occurs only by the slow sedimentation of individual particles. Here we present numerical simulations of the meteorology in Martian cloudy regions that demonstrate that localized convective snowstorms can occur on Mars. We show that such snowstorms—or Ice microbursts—can explain deep night-time mixing layers detected from orbit and precipitation signatures detected below water-Ice Clouds by the Phoenix lander. In our simulations, convective snowstorms occur only during the Martian night, and result from atmospheric instability due to radiative cooling of water-Ice cloud particles. This triggers strong convective plumes within and below Clouds, with fast snow precipitation resulting from the vigorous descending currents. Night-time convection in Martian water-Ice Clouds and the associated snow precipitation lead to transport of water both above and below the mixing layers, and thus would affect Mars’ water cycle past and present, especially under the high-obliquity conditions associated with a more intense water cycle.
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global climate modeling of the martian water cycle with improved microphysics and radiatively active water Ice Clouds
Journal of Geophysical Research, 2014Co-Authors: T Navarro, Francois Forget, Franck Montmessin, Jeanbaptiste Madeleine, Aymeric Spiga, Ehouarn Millour, Anni MaattanenAbstract: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 Meteorologie 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.
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global climate modeling of the martian water cycle with improved microphysics and radiatively active water Ice Clouds
arXiv: Earth and Planetary Astrophysics, 2013Co-Authors: T Navarro, Francois Forget, Jeanbaptiste Madeleine, Aymeric Spiga, Ehouarn Millour, Franck MontmessinAbstract:Radiative effects of water Ice Clouds have noteworthy consequences on the Martian atmosphere, its thermal structure and circulation. Accordingly, the inclusion of such effects in the LMD Mars Global Climate Model (GCM) greatly modifies the simulated Martian water cycle. The intent of this paper is to address the impact of radiatively active Clouds on atmospheric water vapor and Ice in the GCM and improve its representation. We propose a new enhanced modeling of the water cycle, consisting of detailed cloud microphysics with dynamic condensation nuclei and a better implementation of perennial surface water Ice. This physical modeling is based on tunable parameters. This new version of the GCM is compared to the Thermal Emission Spectrometer observations of the water cycle. Satisfying results are reached for both vapor and cloud opacities. However, simulations yield a lack of water vapor in the tropics after Ls=180{\deg} which is persistent in simulations compared to observations, as a consequence of aphelion cloud radiative effects strengthening the Hadley cell. Every year, our GCM simulations indicate that permanent surface water Ice on the north polar cap increases at latitudes higher than 80{\deg}N and decreases at lower latitudes. Supersaturation above the hygropause is predicted in line with SPICAM observations. The model also shows for the first time that the scavenging of dust by water Ice Clouds alone fails to fully account for observed dust detached layers.
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3d modelling of the early martian climate under a denser co2 atmosphere temperatures and co2 Ice Clouds
Icarus, 2013Co-Authors: Francois Forget, Jeanbaptiste Madeleine, Ehouarn Millour, Robin Wordsworth, L Kerber, Jeremy Leconte, Emmanuel Marcq, R M HaberleAbstract: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 C 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 C (a condition which could have allowed rivers and lakes to form) are predicted for obliquity larger than 40 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.
Patrick Minnis - One of the best experts on this subject based on the ideXlab platform.
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a two habit model for the microphysical and optical properties of Ice Clouds
Atmospheric Chemistry and Physics, 2014Co-Authors: Chuntao Liu, Andrew J Heymsfield, Patrick Minnis, Ping Yang, Norman G Loeb, Seiji Kato, Carl G SchmittAbstract:Abstract. To provide a better representation of natural Ice Clouds, a novel Ice cloud model is developed by assuming an Ice cloud to consist of an ensemble of hexagonal columns and 20-element aggregates with specific habit fractions at each particle size bin. The microphysical and optical properties of this two-habit model (THM) are compared with both laboratory and in situ measurements, and its performance in downstream satellite remote sensing applications is assessed. The Ice water contents and median mass diameters calculated based on the THM closely agree with in situ measurements made during 11 field campaigns. In this study, the scattering, absorption, and polarization properties of Ice crystals are calculated with a combination of the invariant imbedding T matrix, pseudo-spectral time domain, and improved geometric-optics methods over an entire practical range of particle sizes. The phase functions, calculated based on the THM, show close agreement with counterparts from laboratory and in situ measurements and from satellite-based retrievals. When the THM is applied to the retrievals of cloud microphysical and optical properties from MODIS (the Moderate Resolution Imaging Spectroradiometer) observations, excellent spectral consistency is achieved; specifically, the retrieved cloud optical thicknesses based on the visible/near infrared bands and the thermal infrared bands agree quite well. Furthermore, a comparison between the polarized reflectivities observed by the PARASOL satellite and from theoretical simulations illustrates that the THM can be used to represent Ice cloud polarization properties.
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estimating the top altitude of optically thick Ice Clouds from thermal infrared satellite observations using calipso data
Geophysical Research Letters, 2008Co-Authors: Patrick Minnis, Christopher R Yost, Sunny Sunmack, Yan ChenAbstract:[1] The difference between cloud-top altitude Ztop and infrared effective radiating height Zeff for optically thick Ice Clouds is examined using April 2007 data taken by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and the Moderate-Resolution Imaging Spectroradiometer (MODIS). For even days, the difference ΔZ between CALIPSO Ztop and MODIS Zeff is 1.58 ± 1.26 km. The linear fit between Ztop and Zeff, applied to odd-day data, yields a difference of 0.03 ± 1.21 km and can be used to estimate Ztop from any infrared-based Zeff for thick Ice Clouds. Random errors appear to be due primarily to variations in cloud Ice-water content (IWC). Radiative transfer calculations show that ΔZ corresponds to an optical depth of ∼1, which based on observed Ice-particle sizes yields an average cloud-top IWC of ∼0.015 gm−3, a value consistent with in situ measurements. The analysis indicates potential for deriving cloud-top IWC using dual-satellite data.
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nitric acid particles in cold thick Ice Clouds observed at global scale link with lightning temperature and upper tropospheric water vapor
Journal of Geophysical Research, 2007Co-Authors: Hélène Chepfer, Marjolaine Chiriaco, Patrick Minnis, Sunny Sunmack, Philippe Dubuisson, Emmanuel RiviereAbstract:Signatures of nitric acid particles (NAP) in cold thick Ice Clouds have been derived from satellite observations. Most NAP are detected in the tropics (9 to 20% of Clouds with T < 202.5 K). Higher occurrences were found in the rare midlatitudes very cold Clouds. NAP occurrence increases as cloud temperature decreases, and NAP are more numerous in January than July. Comparisons of NAP and lightning distributions show that lightning seems to be the main source of the NOx, which forms NAP in cold Clouds over continents. Qualitative comparisons of NAP with upper tropospheric humidity distributions suggest that NAP may play a role in the dehydration of the upper troposphere when the tropopause is colder than 195 K.
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an intercomparison of microphysical retrieval algorithms for upper tropospheric Ice Clouds
Bulletin of the American Meteorological Society, 2007Co-Authors: Jennifer M. Comstock, David L. Mitchell, Patrick Minnis, Sergey Y Matrosov, Kenneth Sassen, Daniel H. Deslover, Gerald G. Mace, Sally A. Mcfarlane, Robert P Dentremont, Matthew D. ShupeAbstract:The large horizontal extent, location in the cold upper troposphere, and Ice composition make cirrus Clouds important modulators of the earth's radiation budget and climate. Cirrus cloud microphysical properties are difficult to measure and model because they are inhomogeneous in nature and their Ice crystal size distribution and habit are not well characterized. Accurate retrievals of cloud properties are crucial for improving the representation of cloud scale processes in large-scale models and for accurately predicting the earth's future climate. A number of passive and active remote sensing retrieval algorithms exist for estimating the microphysical properties of upper tropospheric Clouds. We believe significant progress has been made in the evolution of these retrieval algorithms in the last decade, however, there is room for improvement. Members of the Atmospheric Radiation measurement program (ARM) Cloud properties Working Group are involved in an intercomparison of optical depth(tau), Ice water path, and characteristic particle size in Clouds retrieved using ground-based instruments. The goals of this intercomparison are to evaluate the accuracy of state-of-the-art algorithms, quantify the uncertainties, and make recommendations for improvement.
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Comparison of CALIPSO-like, LaRC, and MODIS retrievals of Ice-cloud properties over SIRTA in France and Florida during CRYSTAL-FACE
Journal of Applied Meteorology and Climatology, 2007Co-Authors: Marjolaine Chiriaco, Hélène Chepfer, Pierrette Dubuisson, Darrel Baumgardner, Mark Mcgill, Martial Haeffelin, Steven Platnick, Véronique Noël, Patrick Minnis, Jacques PelonAbstract:This study compares cirrus-cloud properties and, in particular, particle effective radius retrieved by a Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)-like method with two similar methods using Moderate-Resolution Imaging Spectroradiometer ( MODIS), MODIS Airborne Simulator (MAS), and Geostationary Operational Environmental Satellite imagery. The CALIPSO-like method uses lidar measurements coupled with the split-window technique that uses the infrared spectral information contained at the 8.65-, 11.15-, and 12.05-mu m bands to infer the microphysical properties of cirrus Clouds. The two other methods, using passive remote sensing at visible and infrared wavelengths, are the operational MODIS cloud products (using 20 spectral bands from visible to infrared, referred to by its archival product identifier MOD06 for MODIS Terra) and MODIS retrievals performed by the Clouds and the Earth's Radiant Energy System (CERES) team at Langley Research Center (LaRC) in support of CERES algorithms (using 0.65-, 3.75-, 10.8-, and 12.05-mu m bands); the two algorithms will be referred to as the MOD06 and LaRC methods, respectively. The three techniques are compared at two different latitudes. The midlatitude Ice-Clouds study uses 16 days of observations at the Palaiseau ground-based site in France [Site Instrumental de Recherche par Teledetection Atmospherique (SIRTA)], including a ground-based 532-nm lidar and the MODIS overpasses on the Terra platform. The tropical Ice-Clouds study uses 14 different flight legs of observations collected in Florida during the intensive field experiment known as the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE), including the airborne cloud-physics lidar and the MAS. The comparison of the three methods gives consistent results for the particle effective radius and the optical thickness but discrepancies in cloud detection and altitudes. The study confirms the value of an active remote sensing method (CALIPSO like) for the study of subvisible Ice Clouds, in both the midlatitudes and Tropics. Nevertheless, this method is not reliable in optically very thick tropical Ice Clouds, because of their particular microphysical properties.
Franck Montmessin - One of the best experts on this subject based on the ideXlab platform.
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Martian water Ice Clouds during the 2018 global dust storm as observed by the ACS-MIR channel onboard the Trace Gas Orbiter
Journal of Geophysical Research. Planets, 2020Co-Authors: Aurélien Stcherbinine, Franck Montmessin, Oleg Korablev, M. Vincendon, M. J. Wolff, A. Fedorova, Alexander Trokhimovskiy, A. Patrakeev, Gaetan Lacombe, Lucio BaggioAbstract: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 μm 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 ≤ 2 μm, and applied it to observations gathered between Ls = 165◦ and Ls = 243◦. 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 (reff ≤ 0.3 μm) 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 (reff ≥ 1.5 μm) 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.
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snow precipitation on mars driven by cloud induced night time convection
Nature Geoscience, 2017Co-Authors: Aymeric Spiga, Francois Forget, T Navarro, Ehouarn Millour, D P Hinson, J B Madeleine, Franck MontmessinAbstract:Although it contains less water vapour than Earth’s atmosphere, the Martian atmosphere hosts Clouds. These Clouds, composed of water-Ice particles, influence the global transport of water vapour and the seasonal variations of Ice deposits. However, the influence of water-Ice Clouds on local weather is unclear: it is thought that Martian Clouds are devoid of moist convective motions, and snow precipitation occurs only by the slow sedimentation of individual particles. Here we present numerical simulations of the meteorology in Martian cloudy regions that demonstrate that localized convective snowstorms can occur on Mars. We show that such snowstorms—or Ice microbursts—can explain deep night-time mixing layers detected from orbit and precipitation signatures detected below water-Ice Clouds by the Phoenix lander. In our simulations, convective snowstorms occur only during the Martian night, and result from atmospheric instability due to radiative cooling of water-Ice cloud particles. This triggers strong convective plumes within and below Clouds, with fast snow precipitation resulting from the vigorous descending currents. Night-time convection in Martian water-Ice Clouds and the associated snow precipitation lead to transport of water both above and below the mixing layers, and thus would affect Mars’ water cycle past and present, especially under the high-obliquity conditions associated with a more intense water cycle.
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global climate modeling of the martian water cycle with improved microphysics and radiatively active water Ice Clouds
Journal of Geophysical Research, 2014Co-Authors: T Navarro, Francois Forget, Franck Montmessin, Jeanbaptiste Madeleine, Aymeric Spiga, Ehouarn Millour, Anni MaattanenAbstract: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 Meteorologie 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.
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global climate modeling of the martian water cycle with improved microphysics and radiatively active water Ice Clouds
arXiv: Earth and Planetary Astrophysics, 2013Co-Authors: T Navarro, Francois Forget, Jeanbaptiste Madeleine, Aymeric Spiga, Ehouarn Millour, Franck MontmessinAbstract:Radiative effects of water Ice Clouds have noteworthy consequences on the Martian atmosphere, its thermal structure and circulation. Accordingly, the inclusion of such effects in the LMD Mars Global Climate Model (GCM) greatly modifies the simulated Martian water cycle. The intent of this paper is to address the impact of radiatively active Clouds on atmospheric water vapor and Ice in the GCM and improve its representation. We propose a new enhanced modeling of the water cycle, consisting of detailed cloud microphysics with dynamic condensation nuclei and a better implementation of perennial surface water Ice. This physical modeling is based on tunable parameters. This new version of the GCM is compared to the Thermal Emission Spectrometer observations of the water cycle. Satisfying results are reached for both vapor and cloud opacities. However, simulations yield a lack of water vapor in the tropics after Ls=180{\deg} which is persistent in simulations compared to observations, as a consequence of aphelion cloud radiative effects strengthening the Hadley cell. Every year, our GCM simulations indicate that permanent surface water Ice on the north polar cap increases at latitudes higher than 80{\deg}N and decreases at lower latitudes. Supersaturation above the hygropause is predicted in line with SPICAM observations. The model also shows for the first time that the scavenging of dust by water Ice Clouds alone fails to fully account for observed dust detached layers.
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hyperspectral imaging of convective co2 Ice Clouds in the equatorial mesosphere of mars
Journal of Geophysical Research, 2007Co-Authors: Franck Montmessin, Francois Forget, B Gondet, J P Bibring, Y Langevin, P Drossart, T FouchetAbstract:[1] A unique feature of the Martian climate is the possibility for carbon dioxide, the main atmospheric constituent, to condense as Ice. CO2 Ice is usually detected as frost but is also known to exist as Clouds. This paper presents the first unambiguous observation of CO2 Ice Clouds on Mars. These images were obtained by the visible and near-infrared imaging spectrometer OMEGA on board Mars Express. The data set encompasses 19 different occurrences. Compositional identification is based on the detection of a diagnostic spectral feature around 4.26 μm which is produced by resonant scattering of solar photons by mesospheric CO2 Ice particles in a spectral interval otherwise dominated by saturated gaseous absorption. Observed Clouds exhibit a strong seasonal and geographic dependence, concentrating in the near-equatorial regions during two periods before and after northern summer solstIce (Ls 45° and 135°). Radiative transfer modeling indicates that the 4.26 μm feature is very sensitive to cloud altitude, opacity, and particle size, thereby explaining the variety of spectra associated with the cloud images. On two orbits, the simultaneous detection of Clouds with their shadow provides straightforward and robust estimates of cloud properties. These images confirm the conclusions established from modeling: Clouds are thick, with normal opacities greater than 0.2 in the near infrared, and are lofted in the mesosphere above 80 km. The mean radius of CO2 Ice crystals is found to exceed 1 μm, an unexpected value considering this altitude range. This finding implies the existence of high-altitude atmospheric updrafts which are strong enough to counteract the rapid gravitational fall of particles. This statement is consistent with the cumuliform morphology of the Clouds which may be linked to a moist convective origin generated by the latent heat released during CO2 condensation.
Jeanbaptiste Madeleine - One of the best experts on this subject based on the ideXlab platform.
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retrieval of the water Ice column and physical properties of water Ice Clouds in the martian atmosphere using the omega imaging spectrometer
Icarus, 2021Co-Authors: Kevin Olsen, Francois Forget, Jeanbaptiste Madeleine, A Szantai, Joachim Audouard, A Geminale, F Altieri, G Bellucci, F Oliva, L MontaboneAbstract:Abstract Using spectral images recorded by the OMEGA instrument on Mars Express (Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activite), we are able to derive physical properties of aerosols in water-Ice Clouds on Mars for a distribution of pixels over an observed cloud formation. These properties, mean effective radius, reff, and optical depth (at 0.67 μm), τi, were used to estimate the water Ice-column (WIC), and we found an empirical relationship between the WIC and an Ice cloud index (ICI). The overall mean of retrieved reff is ∼2.2 μm, with a standard deviation of 0.8 μm, and cloud formations with reff between 4.4 and 5.4 μm are observed. The optical depth varies between 0.2 and 2.0. The OMEGA spectra are primarily sensitive to water Ice mass due to absorption, and we find that the ICI, very easy to compute, is a good proxy for the mass of the water-Ice column (WIC) along the optical line of sight. Our retrieval of physical properties is limited in time (to before 2010) by the exhaustion of coolant for one of the OMEGA channels, and in space (to equatorial observations between 140∘W and 90∘E) by the availability of surface albedo measurements. However, we used the ICI to compute WIC values for the entire OMEGA data set, which has near-global coverage for Mars years 26–32, and we present a climatology of the WIC derived from the OMEGA data, which features enhancements on the order of 1.2–1.6 pr. μm over the aphelion cloud belt, and 1.5–2.5 pr. μm over the polar hoods. The data set analyzed is for observations between 140°W and 90°E, and between 35∘S and 35∘N. No restriction is placed on season, but the majority of cloudy observations were during the aphelion period from Ls 35∘ to 135∘. This work was motivated by the ability of the OMEGA instrument to observe the distribution of water-Ice cloud physical properties, and by the availability of new a priori data sets, especially multi-spectral, aerosol-free surface albedo retrieved from a subset of the OMEGA data featuring a cloud-free sky. The main limitations of the retrieval algorithm are linked to the uncertainties on surface albedo, the dust opacity, and the quantity of water-Ice suspended in the atmosphere, which can lead to spectral fits with lower accuracy or unrealistic results. We present distributions of each retrieved parameter, goodness of fit, ICI, and cloud mass, and our investigation of relationships between each parameter. Our approach was to maximize the amount of data analyzed, apply stringent data quality cuts and take a statistical approach to interpretation.
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global climate modeling of the martian water cycle with improved microphysics and radiatively active water Ice Clouds
Journal of Geophysical Research, 2014Co-Authors: T Navarro, Francois Forget, Franck Montmessin, Jeanbaptiste Madeleine, Aymeric Spiga, Ehouarn Millour, Anni MaattanenAbstract: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 Meteorologie 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.
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global climate modeling of the martian water cycle with improved microphysics and radiatively active water Ice Clouds
arXiv: Earth and Planetary Astrophysics, 2013Co-Authors: T Navarro, Francois Forget, Jeanbaptiste Madeleine, Aymeric Spiga, Ehouarn Millour, Franck MontmessinAbstract:Radiative effects of water Ice Clouds have noteworthy consequences on the Martian atmosphere, its thermal structure and circulation. Accordingly, the inclusion of such effects in the LMD Mars Global Climate Model (GCM) greatly modifies the simulated Martian water cycle. The intent of this paper is to address the impact of radiatively active Clouds on atmospheric water vapor and Ice in the GCM and improve its representation. We propose a new enhanced modeling of the water cycle, consisting of detailed cloud microphysics with dynamic condensation nuclei and a better implementation of perennial surface water Ice. This physical modeling is based on tunable parameters. This new version of the GCM is compared to the Thermal Emission Spectrometer observations of the water cycle. Satisfying results are reached for both vapor and cloud opacities. However, simulations yield a lack of water vapor in the tropics after Ls=180{\deg} which is persistent in simulations compared to observations, as a consequence of aphelion cloud radiative effects strengthening the Hadley cell. Every year, our GCM simulations indicate that permanent surface water Ice on the north polar cap increases at latitudes higher than 80{\deg}N and decreases at lower latitudes. Supersaturation above the hygropause is predicted in line with SPICAM observations. The model also shows for the first time that the scavenging of dust by water Ice Clouds alone fails to fully account for observed dust detached layers.
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3d modelling of the early martian climate under a denser co2 atmosphere temperatures and co2 Ice Clouds
Icarus, 2013Co-Authors: Francois Forget, Jeanbaptiste Madeleine, Ehouarn Millour, Robin Wordsworth, L Kerber, Jeremy Leconte, Emmanuel Marcq, R M HaberleAbstract: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 C 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 C (a condition which could have allowed rivers and lakes to form) are predicted for obliquity larger than 40 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.
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the influence of radiatively active water Ice Clouds on the martian climate
Geophysical Research Letters, 2012Co-Authors: Francois Forget, T Navarro, Jeanbaptiste Madeleine, Ehouarn Millour, Aymeric SpigaAbstract:[1] Radiatively active water Ice Clouds (RAC) play a key role in shaping the thermal structure of the Martian atmosphere. In this paper, RAC are implemented in the LMD Mars Global Climate Model (GCM) and the simulated temperatures are compared to Thermal Emission Spectrometer observations over a full year. RAC change the temperature gradients and global dynamics of the atmosphere and this change in dynamics in turn implies large-scale adiabatic temperature changes. Therefore, Clouds have both a direct and indirect effect on atmospheric temperatures. RAC successfully reduce major GCM temperature biases, especially in the regions of formation of the aphelion cloud belt where a cold bias of more than 10 K is corrected. Departures from the observations are however seen in the polar regions, and highlight the need for better modeling of cloud formation and evolution.
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improved Ice particle optical property simulations in the ultraviolet to far infrared regime
Journal of Quantitative Spectroscopy & Radiative Transfer, 2017Co-Authors: Ping YangAbstract:Abstract To derive the bulk radiative properties of Ice Clouds, aircraft contrails and snow grains, which are fundamental to atmospheric radiative transfer calculations in downstream applications, it is necessary to accurately simulate the scattering of light by individual Ice particles. An Ice particle optical property database reported in 2013 (hereafter, TAMUIce2013) is updated (hereafter, TAMUIce2016) to incorporate recent advances in computation of the optical properties of nonspherical particles. Specifically, we employ the invariant imbedding T-matrix (II-TM) method to compute the optical properties of particles with small to moderate size parameters. Both versions use the Improved Geometric Optics Method (IGOM) to compute the optical properties of large Ice crystals, but TAMUIce2016 improves the treatment of inhomogeneous waves inside the scattering particles in the case where Ice is absorptive such as at infrared wavelengths. To bridge the gap between the extinction efficiencies computed from the II-TM and the IGOM, TAMUIce2016 includes spectrally dependent higher order terms of the edge effect in addition to the first order counterpart considered in TAMUIce2013. Furthermore, the differences between TAMUIce2013 and TAMUIce2016 are quantified with respect to the computation of the bulk optical properties of Ice Clouds.
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Ice cloud backscatter study and comparison with calipso and modis satellite data
Optics Express, 2016Co-Authors: Jiachen Ding, Steven Platnick, Ping Yang, R Holz, Kerry Meyer, Mark A Vaughan, Michael D KingAbstract:An invariant imbedding T-matrix (II-TM) method is used to calculate the single-scattering properties of 8-column aggregate Ice crystals. The II-TM based backscatter values are compared with those calculated by the improved geometric-optics method (IGOM) to refine the backscattering properties of the Ice cloud radiative model used in the MODIS Collection 6 cloud optical property product. The integrated attenuated backscatter-to-cloud optical depth (IAB-ICOD) relation is derived from simulations using a CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite) lidar simulator based on a Monte Carlo radiative transfer model. By comparing the simulation results and co-located CALIPSO and MODIS (Moderate Resolution Imaging Spectroradiometer) observations, the non-uniform zonal distribution of Ice Clouds over ocean is characterized in terms of a mixture of smooth and rough Ice particles. The percentage of the smooth particles is approximately 6% and 9% for tropical and midlatitude Ice Clouds, respectively.
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On the radiative properties of Ice Clouds: Light scattering, remote sensing, and radiation parameterization
Advances in Atmospheric Sciences, 2015Co-Authors: Ping Yang, Kuo-nan Liou, Bingqi Yi, Lei Bi, Chao Liu, Bryan A. BaumAbstract:Presented is a review of the radiative properties of Ice Clouds from three perspectives: light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the single-scattering properties of individual Ice crystals. The strengths and weaknesses associated with each approach are discussed. With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared (IR) bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic Ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement Ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed. The performance of Ice cloud models based on the use of different Ice habits to represent Ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for Ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models (GCMs). The availability of the single-scattering properties of complex Ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical Ice particle models in GCM simulations for climate studies is proven.
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a two habit model for the microphysical and optical properties of Ice Clouds
Atmospheric Chemistry and Physics, 2014Co-Authors: Chuntao Liu, Andrew J Heymsfield, Patrick Minnis, Ping Yang, Norman G Loeb, Seiji Kato, Carl G SchmittAbstract:Abstract. To provide a better representation of natural Ice Clouds, a novel Ice cloud model is developed by assuming an Ice cloud to consist of an ensemble of hexagonal columns and 20-element aggregates with specific habit fractions at each particle size bin. The microphysical and optical properties of this two-habit model (THM) are compared with both laboratory and in situ measurements, and its performance in downstream satellite remote sensing applications is assessed. The Ice water contents and median mass diameters calculated based on the THM closely agree with in situ measurements made during 11 field campaigns. In this study, the scattering, absorption, and polarization properties of Ice crystals are calculated with a combination of the invariant imbedding T matrix, pseudo-spectral time domain, and improved geometric-optics methods over an entire practical range of particle sizes. The phase functions, calculated based on the THM, show close agreement with counterparts from laboratory and in situ measurements and from satellite-based retrievals. When the THM is applied to the retrievals of cloud microphysical and optical properties from MODIS (the Moderate Resolution Imaging Spectroradiometer) observations, excellent spectral consistency is achieved; specifically, the retrieved cloud optical thicknesses based on the visible/near infrared bands and the thermal infrared bands agree quite well. Furthermore, a comparison between the polarized reflectivities observed by the PARASOL satellite and from theoretical simulations illustrates that the THM can be used to represent Ice cloud polarization properties.
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Simulation of the optical properties of plate aggregates for application to the remote sensing of cirrus Clouds
Applied Optics, 2011Co-Authors: Ping Yang, Bryan A. Baum, George W. Kattawar, Yongxiang HuAbstract:In regions of deep tropical convection, Ice particles often undergo aggregation and form complex chains. To investigate the effect of the representation of aggregates on electromagnetic scattering calculations, we developed an algorithm to efficiently specify the geometries of aggregates and to compute some of their geometric parameters, such as the projected area. Based on in situ observations, Ice aggregates are defined as clusters of hexagonal plates with a chainlike overall shape, which may have smooth or roughened surfaces. An aggregate representation is developed with 10 ensemble members, each consisting of between 4–12 hexagonal plates. The scattering properties of an individual aggregate Ice particle are computed using either the discrete dipole approximation or an improved geometric optics method, depending upon the size parameters. Subsequently, the aggregate properties are averaged over all geometries. The scattering properties of the aggregate representation closely agree with those computed from 1000 different aggregate geometries. As a result, the aggregate representation provides an accurate and computationally efficient way to represent all aggregates occurring within Ice Clouds. Furthermore, the aggregate representation can be used to study the influence of these complex Ice particles on the satellite-based remote sensing of Ice Clouds. The computed cloud reflectances for aggregates are different from those associated with randomly oriented individual hexagonal plates. When aggregates are neglected, simulated cloud reflectances are generally lower at visible and shortwave-infrared wavelengths, resulting in smaller effective particle sizes but larger optical thicknesses.
