We have reconstructed longitude‐latitude maps of column dust optical depth (CDOD) for Martian year (MY) 34 (5 May 2017– 23 March 2019), using observations by the Mars Climate Sounder (MCS) aboard ...NASA's Mars Reconnaissance Orbiter spacecraft. Our methodology works by gridding a combination of standard (v5.2) and novel (v5.3.2) estimates of CDOD from MCS limb observations, using an improved “Iterative Weighted Binning.” In this work, we have produced four gridded CDOD maps per sol, at different Mars Universal Times. Together with the seasonal and daily variability, the use of several maps per sol also allows us to explore the diurnal variability of CDOD in the MCS dataset, which is shown to be particularly strong during the MY 34 equinoctial global dust event (GDE). In order to understand whether the diurnal variability of CDOD has a physical explanation, and examine the impact of the MY 34 GDE on some aspects of the atmospheric circulation, we have carried out numerical simulations with the “Laboratoire de Météorologie Dynamique” Mars Global Climate Model. We show that the model is able to account for at least part of the observed CDOD diurnal variability. This is particularly true in the southern hemisphere where a strong diurnal wave at the time of the GDE is able to displace dust horizontally as well as vertically. The simulations also clearly show the impact of the MY 34 GDE on the mean meridional circulation and the super‐rotating equatorial jet, similarly to the effects of the equinoctial GDE in MY 25.
Plain Language Summary
Large dust storms on Mars have dramatic impacts on the entire atmosphere but may also have critical consequences for robotic and future human missions. Therefore, there is compelling need to produce an accurate reconstruction of their spatial and temporal evolution for a variety of applications, including to guide Mars climate model simulations. The Martian year 34 (5 May 2017–23 March 2019) represents a very interesting case because an extreme dust event occurred near the time of the northern autumn equinox, consisting of multiple large dust storms engulfing all longitudes and most latitudes with dust for more than 150 Martian days (“sols”). We have used satellite observations from the Mars Climate Sounder instrument aboard NASA's Mars Reconnaissance Orbiter to reconstruct longitude‐latitude maps of the opacity of the atmospheric column due to the presence of dust at several times in each sol of Martian year 34. These maps allow us to analyze the seasonal, day‐to‐day, and day‐night variability of dust in the atmospheric column, which is particularly intense during the extreme dust event. We have also used simulations with a Mars climate model to show that the strong day‐night variability may be partly explained by the large‐scale circulation.
Key Points
We reconstruct subdaily maps of column dust optical depth for Martian year 34 to be used for data analysis and modeling
We observe seasonal, daily, and diurnal variability in the column dust, notably during the global dust event (GDE)
Simulations with a global climate model examine the impact of the GDE on the atmospheric circulation and diurnal variability of column dust
The loss of water from Mars to space is thought to result from the transport of water to the upper atmosphere, where it is dissociated to hydrogen and escapes the planet. Recent observations have ...suggested large, rapid seasonal intrusions of water into the upper atmosphere, boosting the hydrogen abundance. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution by altitude. Water profiles during the 2018-2019 southern spring and summer stormy seasons show that high-altitude water is preferentially supplied close to perihelion, and supersaturation occurs even when clouds are present. This implies that the potential for water to escape from Mars is higher than previously thought.
It has been suggested that the recently discovered exoplanet GJ581d might be able to support liquid water due to its relatively low mass and orbital distance. However, GJ581d receives 35% less ...stellar energy than Mars and is probably locked in tidal resonance, with extremely low insolation at the poles and possibly a permanent night side. Under such conditions, it is unknown whether any habitable climate on the planet would be able to withstand global glaciation and/or atmospheric collapse. Here we present three-dimensional climate simulations which demonstrate that GJ581d will have a stable atmosphere and surface liquid water for a wide range of plausible cases, making it the first confirmed super-Earth (exoplanet of 2-10 Earth masses) in the habitable zone. We find that atmospheres with over 10 bar CO2 and varying amounts of background gas (e.g., N2) yield global mean temperatures above 0?C for both land and ocean-covered surfaces. Based on the emitted IR radiation calculated by the model, we propose observational tests that will allow these cases to be distinguished from other possible scenarios in the future.
The Cassini mission unveiled the intense and diverse activity in Saturn's atmosphere: banded jets, waves, vortices, equatorial oscillations. To set the path towards a better understanding of those ...phenomena, we performed high-resolution multi-annual numerical simulations of Saturn's atmospheric dynamics. We built a new Global Climate Model GCM for Saturn, named the Saturn DYNAMICO GCM, by combining a radiative-seasonal model tailored for Saturn to a hydrodynamical solver based on an icosahedral grid suitable for massively-parallel architectures. The impact of numerical dissipation, and the conservation of angular momentum, are examined in the model before a reference simulation employing the Saturn DYNAMICO GCM with a 1/2° latitude-longitude resolution is considered for analysis. Mid-latitude banded jets showing similarity with observations are reproduced by our model. Those jets are accelerated and maintained by eddy momentum transfers to the mean flow, with the magnitude of momentum fluxes compliant with the observed values. The eddy activity is not regularly distributed with time, but appears as bursts; both barotropic and baroclinic instabilities could play a role in the eddy activity. The steady-state latitude of occurrence of jets is controlled by poleward migration during the spin-up of our model. At the equator, a weakly-superrotating tropospheric jet and vertically-stacked alternating stratospheric jets are obtained in our GCM simulations. The model produces Yanai (Rossby-gravity), Rossby and Kelvin waves at the equator, as well as extratropical Rossby waves, and large-scale vortices in polar regions. Challenges remain to reproduce Saturn's powerful superrotating jet and hexagon-shaped circumpolar jet in the troposphere, and downward-propagating equatorial oscillation in the stratosphere.
•A new Global Climate Model for Saturn with radiative transfer•High-resolution numerical simulations on a duration of 15 Saturn years•Results on zonal jets, waves, eddies in Saturn's troposphere
The deuterium to hydrogen (D/H) ratio is commonly used to investigate the history of water on Mars, yet the mechanisms controlling present‐day HDO behavior are poorly understood. Significant ...variations of the D/H ratio were first predicted on the basis of a 3D global climate model, which were later confirmed by ground‐based observations. This behavior, consisting of lower HDO/H2O ratios in the colder regions of Mars, is related to the isotopic fractionation occurring at condensation. We leverage this previous effort and present an updated implementation, using the modern version of the model, that remains in agreement with the older version. We explore the impact of the global dust storm (GDS) that occurred during Martian year 34 (MY34) on HDO. Our simulations indicate that HDO is on average 40% more abundant at 100 km during the MY34 GDS year than during a regular year, with likely large consequences for the escape flux of water that year.
Plain Language Summary
HDO, the semi‐heavy isotope of water, when compared to water, is a good indicator of how much water has been escaping from the atmosphere of Mars over the ages. Ultimately, it can be used to estimate the past reservoir of water available on Mars in its early youth. Because HDO has a slightly higher molecular mass compared to H2O, condensation induces an enrichment of HDO in the ice phase compared with the vapor phase. This subsequently causes spatial and temporal variations of the deuterium to hydrogen ratio. We use a global circulation model to simulate the HDO cycle in the atmosphere. Our model is an upgrade of the previous model presented in Montmessin et al. (2005, Journal of Geophysical Research, 110(E3), E10004. doi:10.1029/2004JE002357). We then simulate the effect of the global dust storm that affected Mars during the summer of 2018, and show that it should have had a strong impact on the vertical distribution of HDO, allowing it to reach higher altitudes. Such simulations are intended to be compared with observations from the Trace Gas Orbiter, currently in orbit around Mars.
Key Points
We reimplemented the HDO cycle in a more recent version of the Laboratoire de Météorologie Dynamique Mars global climate model
We reproduce the observed gradient of the deuterium to hydrogen ratio between cold and warm regions
The global dust storm of Martian year 34 has a strong effect on the vertical distribution of HDO
Thermal tides in the Martian atmosphere are analyzed using temperature profiles retrieved from nadir observations obtained by the TIRVIM Fourier‐spectrometer, part of the Atmospheric Chemistry Suite ...onboard the ExoMars Trace Gas Orbiter. The data is selected near the northern summer solstice at solar longitude (LS) 75°–105° of Martian Year 35. The observations have a full local time coverage, which enables analyses of daily temperature anomalies. The observed zonal mean temperature is lower by 4–6 K at ∼100 Pa, but higher toward the summer pole, compared to the Laboratoire de Météorologie Dynamique (LMD) Mars General Circulation Model (GCM). Wave mode decomposition shows dominant diurnal tide and important semi‐diurnal tide and diurnal Kelvin wave, with maximal amplitudes of 5, 3, and 2.5 K, respectively, from tens to hundreds of Pa. The results generally agree well with the LMD Mars GCM, but with noticeable earlier phases of diurnal (∼1 hr) and semi‐diurnal (∼3 hr) tides.
Plain Language Summary
Unlike the Earth, daily temperature variation on Mars is as large as tens of degrees because of its thin atmosphere. The sunlight absorbed by the Martian surface and dust in the atmosphere leads to dramatic temperature increase in the lower atmosphere during daytime. Such large and regular changes can trigger temperature waves, and some modes of them can propagate into higher altitudes, where they become the major factor controlling the daily temperature variation. In this work, temperature profiles obtained using thermal‐infrared spectra are analyzed. Zonal mean temperature is compared with numerical simulations of the Martian atmosphere. Different types of the wave modes are computed through decomposition. Results from the observation agree well with model prediction when the observation mechanisms are taken into consideration. Estimation of the strength of these waves can be improved in the future with improved design of observation strategies.
Key Points
Thermal tides in the Martian atmosphere are investigated using temperature profiles retrieved from TIRVIM nadir observations
Diurnal tide dominates daily temperature variations; semi‐diurnal tide and diurnal Kelvin wave are also important
Observations agree well with numerical simulations, but suggest phases of diurnal and semi‐diurnal tides earlier than predicted
We report a new water‐ice cloud feature observed during the Mars year 34 global dust storm: twilight cloud bands that routinely formed just past the evening terminator. We use images taken by the ...MAVEN/IUVS instrument. These bands were often latitudinally continuous, spanning over 6,000 km and were present between 18:00 and 19:00 local time. They were present for nearly the entire time IUVS imaged the evening terminator and often reached altitudes of at least 40 to 50 km during the mature phase of the storm. We compare these observations to LMD global climate model simulations. The simulations generally contain the temporal and spatial extents of the bands seen in IUVS data throughout the storm, but there are some discrepancies. We infer that these clouds formed as a result of semidiurnal thermal tides.
Plain Language Summary
Water‐ice clouds and dust are among the most common particles in the Martian atmosphere, but the effect of global dust storms on cloud formation is largely unknown. We observed cloud bands that repeatedly formed near dusk during the Mars year 34 global dust storm. We saw these bands throughout the storm at locations all across the planet. We investigate this feature by using a global climate model, which predicted the formation of these cloud bands as a result of rapidly changing temperatures. The simulations of the bands contain several features seen in our observations, but not all.
Key Points
We observed a new cloud formation phenomenon just after sunset during the Mars year 34 global dust storm in MAVEN/IUVS images
Global climate model simulations are able to reproduce several but not all aspects of our observations
These twilight clouds formed due to semidiurnal thermal tides
We report observations by the Mars Climate Sounder showing strong diurnal variations in temperature and the vertical dust distribution during the 2018 (Mars Year 34) global dust event. The ...temperature field shows weak diurnal tidal activity at equatorial latitudes but a strong diurnal tide in middle to high latitudes with a maximum amplitude of 29 K in the lower atmosphere of the south polar region. The diurnal variability of dust is small in the equatorial region and increases toward higher latitudes. At middle and low latitudes, comparable dust amounts are found about 5–10 km higher in the atmosphere on the dayside than on the nightside. The dust reaches the highest altitudes in the late afternoon and is found at the lowest altitudes in the late night. In the southern high latitudes a persistent cold air mass with low dust content is identified on the nightside of the planet centered at 3–6 a.m. local time. The observed variations are well represented by model simulations with the Laboratoire de Météorologie Dynamique General Circulation Model. Comparisons between data and model results suggest that the diurnal variations in the dust are largely driven by the meridional circulation exhibiting diurnal tidal variations. The model results show that the compact air mass in the south polar region has a high potential vorticity, supporting its interpretation as a remnant of the southern polar vortex, which is forced toward the nightside of the planet due to the enhanced diurnal tide during the global dust event.
Plain Language Summary
One of the most distinctive features of the Martian atmosphere are global dust storms, one of which occurred in 2018. We report on observations of the vertical structure of atmospheric temperature and dust by the Mars Climate Sounder onboard Mars Reconnaissance Orbiter. Strong differences between day and night are found in both temperature and dust vertical structure. The strongest temperature variations are observed in the south polar atmosphere, with temperature differences up to 58 °C/136 °F between day and night. Comparable dust amounts are found 5–10 km (3–6 miles) higher in the atmosphere on the dayside than on the nightside at central and equatorial latitudes. In the southern polar region a persistent cold body of air with low dust is identified on the nightside of the planet. The observations are compared with the results from a global atmospheric computer model. The observed temperature and dust distribution and their variations over the Martian day are well represented by the model. The diurnal variations in the dust are largely driven by diurnal changes in the large‐scale atmospheric circulation. The compact body of air in the south polar region is forced to the nightside by this altered circulation but does not dissipate for several months.
Key Points
The Mars Climate Sounder observes strong diurnal variations in the vertical distribution of dust during the 2018 global dust storm
Dust diurnal variability at low and middle latitudes is largely related to the meridional circulation exhibiting diurnal tidal variations
Diurnal variations at south polar latitudes are related to a remnant of the polar vortex confined to the nightside of the planet
The origin of the detached dust layers observed by the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter is still debated. Spiga et al. (2013, https://doi.org/10.1002/jgre.20046) revealed ...that deep mesoscale convective “rocket dust storms” are likely to play an important role in forming these dust layers. To investigate how the detached dust layers are generated by this mesoscale phenomenon and subsequently evolve at larger scales, a parameterization of rocket dust storms to represent the mesoscale dust convection is designed and included into the Laboratoire de Météorologie Dynamique (LMD) Martian Global Climate Model (GCM). The new parameterization allows dust particles in the GCM to be transported to higher altitudes than in traditional GCMs. Combined with the horizontal transport by large‐scale winds, the dust particles spread out and form detached dust layers. During the Martian dusty seasons, the LMD GCM with the new parameterization is able to form detached dust layers. The formation, evolution, and decay of the simulated dust layers are largely in agreement with the Mars Climate Sounder observations. This suggests that mesoscale rocket dust storms are among the key factors to explain the observed detached dust layers on Mars. However, the detached dust layers remain absent in the GCM during the clear seasons, even with the new parameterization. This implies that other relevant atmospheric processes, operating when no dust storms are occurring, are needed to explain the Martian detached dust layers. More observations of local dust storms could improve the ad hoc aspects of this parameterization, such as the trigger and timing of dust injection.
Plain Language Summary
On Mars, dust is of major importance to the Martian atmosphere, analogous to the importance of water to the Earth's atmosphere. But unlike the water on Earth, the distribution of dust on Mars is still not well understood, particularly the vertical distribution. The Mars Climate Sounder aboard the Mars Reconnaissance Orbiter found that the dust on Mars is detached at ∼20–40 km in altitude in the Martian atmosphere, rather than concentrated in the near‐surface atmosphere and decreasing as the pressure decreases, as scientists have thought since the 1980s. The reason for the detached dust layers is still debated. In this paper, we implemented a modeling study by simulating the small‐scale deep rocket dust storm in a Global Climate Model to explore the origins of the detached dust layers. We found that when the Global Climate Model included rocket dust storms, the simulations produced the detached structures of dust on Mars. This suggests that the rocket dust storm is responsible for the formation of the detached dust layers. Meanwhile, the rocket dust storms cannot reproduce all the detached dust layers observed by Mars Climate Sounder. This implies that some unknown atmospheric processes can also contribute to the existence of the detached dust layers.
Key Points
A parameterization for representing unresolved rocket dust storms in Martian GCM is proposed and employed in simulations with the LMD model
GCM simulations featuring the rocket dust storm parameterization reproduce the detached dust layers observed by MCS during the dusty seasons
The formation of detached dust layers within Mars clear seasons Ls after 270° in MY29 is underestimated in the simulations compared to the observations
The cloud parameterizations of the LMDZ6A climate model (the atmospheric component of the IPSL‐CM6 Earth system model) are entirely described, and the global cloud distribution and cloud radiative ...effects are evaluated against the CALIPSO‐CloudSat and CERES observations. The cloud parameterizations in recent versions of LMDZ favor an object‐oriented approach for convection, with two distinct parameterizations for shallow and deep convection and a coupling between convection and cloud description through the specification of the subgrid‐scale distribution of water. Compared to the previous version of the model (LMDZ5A), LMDZ6A better represents the low‐level cloud distribution in the tropical belt, and low‐level cloud reflectance and cover are closer to the PARASOL and CALIPSO‐GOCCP observations. Mid‐level clouds, which were mostly missing in LMDZ5A, are now better represented globally. The distribution of cloud liquid and ice in mixed‐phase clouds is also in better agreement with the observations. Among identified deficiencies, low‐level cloud covers are too high in mid‐latitude to high‐latitude regions, and high‐level cloud covers are biased low globally. However, the cloud global distribution is significantly improved, and progress has been made in the tuning of the model, resulting in a radiative balance in close agreement with the CERES observations. Improved tuning also revealed structural biases in LMDZ6A, which are currently being addressed through a series of new physical and radiative parameterizations for the next version of LMDZ.
Plain Language Summary
This paper describes the representation of clouds in the latest version of LMDZ, which is a French atmospheric model used for climate change projections. Along with other international climate models, it serves as a basis for the IPCC (Intergovernmental Panel on Climate Change) report by contributing to the CMIP project (Climate Model Intercomparison Project). Clouds are especially important in the climate system because they reflect a lot of sunlight and also absorb and emit a lot of infrared radiation. They can either amplify or reduce the current global warming depending on their change in opacity, altitude, and detailed properties. It is therefore essential to represent them accurately in climate models. The main physical equations used to compute cloud properties in LMDZ are introduced, and the model results are compared to various satellite observations. It reveals that low‐level and mid‐level clouds are in better agreement with the observations than before but that high‐level clouds remain difficult to simulate realistically. Ongoing developments aimed at solving these remaining deficiencies are finally described.
Key Points
Cloud parameterizations of the LMDZ6A climate model are entirely described
Low‐level and mid‐level cloud distribution and radiative effects are improved compared to LMDZ5A
LMDZ6A is better tuned than LMDZ5A, and knowledge of its structural deficiencies has been gained
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