This study presents the global climate model IPSL‐CM6A‐LR developed at Institut Pierre‐Simon Laplace (IPSL) to study natural climate variability and climate response to natural and anthropogenic ...forcings as part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). This article describes the different model components, their coupling, and the simulated climate in comparison to previous model versions. We focus here on the representation of the physical climate along with the main characteristics of the global carbon cycle. The model's climatology, as assessed from a range of metrics (related in particular to radiation, temperature, precipitation, and wind), is strongly improved in comparison to previous model versions. Although they are reduced, a number of known biases and shortcomings (e.g., double Intertropical Convergence Zone ITCZ, frequency of midlatitude wintertime blockings, and El Niño–Southern Oscillation ENSO dynamics) persist. The equilibrium climate sensitivity and transient climate response have both increased from the previous climate model IPSL‐CM5A‐LR used in CMIP5. A large ensemble of more than 30 members for the historical period (1850–2018) and a smaller ensemble for a range of emissions scenarios (until 2100 and 2300) are also presented and discussed.
Plain Language Summary
Climate models are unique tools to investigate the characteristics and behavior of the climate system. While climate models and their components are developed gradually over the years, the sixth phase of the Coupled Model Intercomparison Project (CMIP6) has been the opportunity for the Institut Pierre‐Simon Laplace to develop, test, and evaluate a new configuration of its climate model called IPSL‐CM6A‐LR. The characteristics and emerging properties of this new model are presented in this study. The model climatology, as assessed from a range of metrics, is strongly improved, although a number of biases common to many models do persist. The equilibrium climate sensitivity and transient climate response have both increased from the previous climate model IPSL‐CM5A‐LR used in CMIP5.
Key Points
The IPSL‐CM6A‐LR model climatology is much improved over the previous version, although some systematic biases and shortcomings persist
A long preindustrial control and a large number of historical and scenario simulations have been performed as part of CMIP6
The effective climate sensitivity of the IPSL model increases from 4.1 to 4.8 K between IPSL‐CM5A‐LR and IPSL‐CM6A‐LR
Martian CO2 ice clouds are intriguing features, representing a rare occurrence of atmospheric condensation of a major component. These clouds play a crucial role due to their radiative properties, ...interactions with surface, and coupling with microphysical cycles of aerosols. Observations have been limited, prompting modeling studies to understand their formation and dynamics. Here, we present the first high‐resolution 3D simulations of CO2 ice clouds using a Large‐Eddy Simulation (LES) model incorporating CO2 microphysics. We investigate cloud formation in idealized temperature perturbations in the polar night. A reference simulation with a −2K perturbation demonstrates that the formed CO2 ice cloud possesses a convective potential, leading to its ascent in the troposphere. We determine the timescales and orders of magnitude of various phenomena involved in the lifecycle of a CO2 ice cloud. Sensitivity tests show that convection can be inhibited or intensified by the thermodynamic and microphysical conditions of the simulated environment.
Plain Language Summary
CO2 ice clouds have been observed in the Martian polar nights in the lower atmosphere. These clouds are extremely challenging to observe due to the lack of sunlight. However, they play a significant role in Mars' climate, especially through interactions with the surface and other atmospheric species. To study the formation processes of these clouds, we use a high‐resolution model. Even a relatively weak cooling can lead to the formation of a CO2 ice cloud with convective potential, enabling it to move vertically upward. We determine the characteristic times and altitudes of this phenomenon and investigate how they respond when atmospheric parameters, such as cooling temperature, the presence of extra dust, or horizontal winds are varied. Our findings show that some of these parameters can either inhibit or enhance convection development.
Key Points
Coupling a convection model with a CO2 microphysics scheme can simulate the formation of convective CO2 ice clouds triggered by realistic perturbations
These is a strong coupling between CO2 ice cloud convection and dust cycle in the troposphere
The convective process intensity depends strongly on the number of available condensation nuclei and the temperature of the perturbation
Abstract Martian CO 2 ice clouds are intriguing features, representing a rare occurrence of atmospheric condensation of a major component. These clouds play a crucial role due to their radiative ...properties, interactions with surface, and coupling with microphysical cycles of aerosols. Observations have been limited, prompting modeling studies to understand their formation and dynamics. Here, we present the first high‐resolution 3D simulations of CO 2 ice clouds using a Large‐Eddy Simulation (LES) model incorporating CO 2 microphysics. We investigate cloud formation in idealized temperature perturbations in the polar night. A reference simulation with a −2K perturbation demonstrates that the formed CO 2 ice cloud possesses a convective potential, leading to its ascent in the troposphere. We determine the timescales and orders of magnitude of various phenomena involved in the lifecycle of a CO 2 ice cloud. Sensitivity tests show that convection can be inhibited or intensified by the thermodynamic and microphysical conditions of the simulated environment.
Plain Language Summary CO 2 ice clouds have been observed in the Martian polar nights in the lower atmosphere. These clouds are extremely challenging to observe due to the lack of sunlight. However, they play a significant role in Mars' climate, especially through interactions with the surface and other atmospheric species. To study the formation processes of these clouds, we use a high‐resolution model. Even a relatively weak cooling can lead to the formation of a CO 2 ice cloud with convective potential, enabling it to move vertically upward. We determine the characteristic times and altitudes of this phenomenon and investigate how they respond when atmospheric parameters, such as cooling temperature, the presence of extra dust, or horizontal winds are varied. Our findings show that some of these parameters can either inhibit or enhance convection development.
Key Points Coupling a convection model with a CO 2 microphysics scheme can simulate the formation of convective CO 2 ice clouds triggered by realistic perturbations These is a strong coupling between CO 2 ice cloud convection and dust cycle in the troposphere The convective process intensity depends strongly on the number of available condensation nuclei and the temperature of the perturbation
We have implemented full CO2 ice cloud microphysics into the LMD Mars Global Climate Model (MGCM) and we have conducted the first global simulations. The microphysical model implementation follows ...the modal scheme used for water ice cloud microphysics in the MGCM, but includes specific aspects that need to be accounted for when dealing with CO2 ice clouds. These include nucleation of CO2 on water ice crystals and CO2 condensation theory adapted for the Martian conditions. The model results are compared to available observations globally, and separately for polar regions and equatorial mesosphere. The observed seasonal and latitudinal variability of the CO2 ice clouds is in general reproduced. The polar regions are covered by CO2 ice clouds during the winter as observed. Instead of forming only in the lowest 10–15 km of the atmosphere, they extend up to several tens of kilometers above the surface in the model, dictated by the modeled temperature structure. We have also quantified the contribution of the cloud microphysics to the surface CO2 ice deposits. Snowfall from these clouds contributes up to 10% of the atmosphere–surface ice flux in the polar regions in our simulations, in the range that has been indirectly deduced from observations. In the mesosphere, notable amounts of CO2 ice clouds form only when water ice crystals are used as condensation nuclei in addition to dust particles, and their spatial distribution is in agreement with observations. The mesospheric temperature structure, dominated by tides, dictates the longitudinal and seasonal distribution of these clouds. The seasonal and local time variations of the clouds are not fully reproduced by the model. There is a long pause in CO2 ice cloud formation in the model around the aphelion season, but clouds have been observed during this period, although with a lower apparition frequency. Modeled mesospheric clouds form mainly during the night and in the morning, whereas during the daytime, when most of the cloud observations have been made, the model rarely predicts clouds. These discrepancies could be explained by the strong dependence of the cloud formation process on mesospheric temperatures that are themselves challenging to reproduce and sensitive to the MGCM processes and parameters. The rare possibilities for nighttime observations might also bias the observational climatologies towards daytime detections. Future developments of the model consist in the inclusion of a possible exogenous condensation nucleus source in the mesosphere and the radiative effect of CO2 ice clouds.
•Martian carbon dioxide clouds are reproduced in global climate simulations.•Modeled thick polar CO2 ice clouds contribute to the surface ice cap through snowfall.•Mesospheric CO2 ice clouds form more frequently when they nucleate on water ice crystals.
The Mars Orbiter Laser Altimeter (MOLA) instrument has been drawing a map of Mars' topography between September 1997 and June 2001. It has also been able to observe clouds during the mission ...duration, providing data for the low Martian atmosphere for nearly 1.5 Mars years. The Mars Global Surveyor, which carried MOLA, also carried two other instruments that also observed clouds during the same time period (the Mars Orbiter Camera and the Thermal Emission Spectrometer). Combining observations from these three data sets could provide a complete recap of most atmospheric structures during MY24 and MY25. However, previous studies of MOLA data set often had to use stringent detection criteria. Using machine learning clustering methods, we end up finding way more atmospheric returns. Our results are presented in the form of an atmospheric features catalog that we then use to compare MOLA observations with Mars Orbiter Camera and Thermal Emission Spectrometer results, but also with more recent missions. We study the development of recurrent phenomenon in the Martian atmosphere, like the aphelion cloud belt or the south polar hood, but also spontaneous events such as regional dust storms. Methods could be tuned even more finely by using more complex clustering methods or deep learning algorithms to clearly distinguish atmospheric structures.
Plain Language Summary
The Mars Orbiter Laser Altimeter (MOLA) instrument has been emitting laser pulses toward the Martian surface. Time of flight of the laser before returning to the instrument was originally used to estimate the altitude of Mars' surface, but the sensibility of the detector was good enough to detect clouds’ signatures coming from the atmosphere. We propose that studying the MOLA data set using machine learning methods that gather similar laser returns into groups can enable the formation of a cluster made of atmospheric features, distinguishing them from noise and surface returns. These features are then grouped into clouds or dust structures and compared with other mission results that also observed the Martian atmosphere between 1997 and 2001. This paints a picture of many phenomena in the low Martian atmosphere, their seasonal and interannual variability and their varying intensity.
Key Points
We reanalyze the Mars Orbiter Laser Altimeter data set with clustering methods and retrieve a new, large atmospheric structure data set
Comparing the data set with other observations allows us to provide a global view of atmospheric structures
We observe the development of the aphelion cloud belt, the polar hoods, regional dust storms, and clouds over topographic features
Le LAT est l'instrument principal du satellite Fermi et permet d'étudier le ciel en rayons gamma de 20 MeV à plus de 300 GeV. Sa sensibilité accrue a permis l'augmentation du nombre de sources ...détectées dans le domaine des hautes énergies. Une partie importante de celles-ci n'a pas de contrepartie connue et une étude multi-longueur d'onde est nécessaire afin de comprendre l'origine du signal observé. Dans un premier temps, cette thèse présente l'étude morphologique et spectrale détaillée de la source non-identifiée HESS J1745--303, qui a été découverte dans le domaine gamma par l'expérience H.E.S.S. en 2006 puis analysée spécifiquement dans un article de 2008, à l'aide des données du LAT. Deux sources ponctuelles situées à une localisation proche de HESS J1745-303 sont présentes dans le catalogue à deux ans de données de Fermi (2FGL) mais une analyse dédiée de cette région est néanmoins nécessaire vu sa complexité. Elle est en effet localisée à ~1° du Centre Galactique et à moins de 0.5° du pulsar de la Souris, les deux sources les plus brillantes en gamma dans cette région.Les différents processus d'émission de photons sont présentés dans un second temps. Leurs simulations permettent d'effectuer une étude approfondie de l'origine de l'émission détectée aux hautes et très hautes énergies par le LAT et par H.E.S.S. L'émission de cette source reste en effet encore énigmatique de nos jours et une étude multi-longueur d'onde est effectuée afin de contraindre les modèles d'émission.
The LAT is the main instrument onboard the Fermi space telescope and performs unprecedented observations of the gamma-ray sky between 20 MeV and more than 300 GeV. The number of gamma-ray sources detected has grown thanks to its high sensibility. A large part of these sources has no known counterpart and a multi-wavelength study is needed in order to understand the origin of the observed signal.This thesis presents a morphological and spectral detailed study of the unidentified source HESS J1745--303, which was discovered in gamma-rays in 2006 with the H.E.S.S. experiment, using the Fermi-LAT data. Two point-like sources, located near HESS J1745--303, are included in the Fermi Large Area Telescope Second Source Catalog (2FGL) but, due to the complexity of this region, a dedicated study of the LAT data is however needed. Indeed, its location is ~1° away from the Galactic Center source and less than 0.5° from the Mouse pulsar, the two brightest gamma-ray sources in this region.The astrophysical emission processes are then detailed. We develop an extensive code which allowed us to study the origin of the HE (High Energy) and VHE (Very-High Energy) gamma-ray emissions detected by the LAT and H.E.S.S. The emission of this source is indeed still enigmatic and we perform a mutli-wavelength study to try to constrain the emission modeling.
Le LAT est l'instrument principal du satellite Fermi et permet d'étudier le ciel en rayons gamma de 20 MeV à plus de 300 GeV. Sa sensibilité accrue a permis l'augmentation du nombre de sources ...détectées dans le domaine des hautes énergies. Une partie importante de celles-ci n'a pas de contrepartie connue et une étude multi-longueur d'onde est nécessaire afin de comprendre l'origine du signal observé. Dans un premier temps, cette thèse présente l'étude morphologique et spectrale détaillée de la source non-identifiée HESS J1745--303, qui a été découverte dans le domaine gamma par l'expérience H.E.S.S. en 2006 puis analysée spécifiquement dans un article de 2008, à l'aide des données du LAT. Deux sources ponctuelles situées à une localisation proche de HESS J1745--303 sont présentes dans le catalogue à deux ans de données de Fermi (2FGL) mais une analyse dédiée de cette région est néanmoins nécessaire vu sa complexité. Elle est en effet localisée à ~1° du Centre Galactique et à moins de 0.5° du pulsar de la Souris, les deux sources les plus brillantes en gamma dans cette région. Les différents processus d'émission de photons sont présentés dans un second temps. Leurs simulations permettent d'effectuer une étude approfondie de l'origine de l'émission détectée aux hautes et très hautes énergies par le LAT et par H.E.S.S. L'émission de cette source reste en effet encore énigmatique de nos jours et une étude multi-longueur d'onde est effectuée afin de contraindre les modèles d'émission.
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