The origin of carbon monoxide (CO) in Saturn's stratosphere remains uncertain, with proposed sources including internal thermochemical production, cometary impacts, and exogenic material from the rings and icy moons (i.e. Enceladus). We aim to constrain the vertical and meridional distribution of stratospheric CO and assess the relative contributions of these potential sources. Here, we analysed high-spectral-resolution ALMA observations of the CO (J=3-2) line obtained on 25 May 2018, sampling Saturn's limb from 20°S to 69°N. CO vertical profiles were retrieved using a line-by-line radiative transfer model combined with spectral inversion techniques, testing multiple prior scenarios representative of different source hypotheses. CO is confined to a narrow layer between 0.1 and 1 mbar, with a robust negative vertical gradient and mean abundances of (3.7+/- 0.8) x 10^-8 at 0.1 mbar and (7.2 +/- 0.9) x 10^-8 at 1 mbar. The meridional distribution is statistically homogeneous, with a marginal enhancement near 60° N plausibly related to Enceladus. No significant equatorial enhancement is detected. The absence of a strong equatorial enhancement rules out a long-lived steady source associated with ring infall. The observations are most consistent with a relatively recent (≈200-year-old or younger) cometary impact whose material has since been horizontally mixed, while any Cassini Grand Finale ring influx was either too recent or inefficient to affect CO abundances at the probed pressure levels.

Following the extensive exploration of hot and warm exoplanets over the past two decades, recent improvements in instrumental techniques, from ground and space, have allowed the detection of “temperate” exoplanets, with equilibrium temperatures ranging between 300 and 500 K. Opening this new research field will not only enlarge our comprehension of the various physical properties of exoplanets, but also reduce the comprehension gap between these objects and the planets of our solar system, and provide a key step towards the study of habitable exoplanets. Over the past few years, we have started a program [1, 2] for identifying temperate exoplanets, which would be observable with the Ariel mission in the spectroscopic mode (Tier 2 mode). Using the TESS database and analyzing the observability of the candidates with Ariel, we have selected a list of 15 targets (a gas giant, a few big Neptunes and several super-Earths/sub-Neptunes) for which spectroscopic observations with Ariel would allow a characterization of their atmosphere and possibly an identification of the main atmospheric absorbers [3]. Among this list, the sub-Neptune TOI-1759 b appears as a favorable candidate. With a radius of about 3 earth radii and a mass of about 10 earth masses, TOI-1759 b is most likely a hydrogen-rich planet orbiting a M0.0 star located at 40 pc with a revolution period of 19 days. We have calculated the thermal structure, dis-equilibrium composition and size distribution of cloud and haze particles in its atmosphere using a model that couples self-consistently the involved physical and chemical processes [4]. Cloud nucleation rates reach significant values near a pressure level of 0.35 bar, where the condensing gas species (KCl, NaCl and Zn) approach their saturation limit. We have calculated the infrared synthetic spectrum of TOI-1759 b from the visible up to 20 μm for different metallicities and different haze and cloud conditions. Feasibility studies [5] suggest that information could be retrieved about the target’s atmosphere with 16 primary transit observations with Ariel (which could be achieved over a time range of less than a year), or a single primary transit observation with the JWST. [1] Encrenaz, T. et al., Exp. Astr. 46, 31 (2018) [2] Encrenaz, T. et al., Exp. Astr. 53, 375 (2022).[3] Encrenaz, T. et al. Poster presented at the EGU General Assembly, Vienna, April 2023.[4] Arfaux & Lavvas, MNRAS, 515, 4753 (2022).[5] Tinetti et al., Exp.Astr. 46, 135 (2018).

This paper presents an analysis of large-scale vortices in the atmospheres of gas giants, focusing on a detailed study conducted using the Saturn-DYNAMICO global climate model (GCM). Large-scale vortices, a prominent feature of gas giant atmospheres, play a critical role in their atmospheric dynamics. By employing three distinct methods - manual detection, machine learning via artificial neural networks (ANN), and dynamical detection using the Automated Eddy-Detection Algorithm (AMEDA) - we characterise the spatial, temporal, and dynamical properties of these vortices within the Saturn-DYNAMICO GCM. Our findings reveal a consistent production of vortices due to well-resolved eddy-to-mean flow interactions, exhibiting size and intensity distributions broadly in agreement with observational data. However, notable differences in vortex location, size, and concentration highlight the model's limitations and suggest areas for further refinement. The analysis underscores the importance of zonal wind conditions in influencing vortex characteristics and suggests that more accurate modelling of giant planet vortices may require improved representation of moist convection and jet structure. This study not only provides insights into the dynamics of Saturn's atmosphere as simulated by the GCM but also offers a framework for comparing vortex characteristics across observations and models of planetary atmospheres.

The transfer of momentum due to non‐orographic Gravity Waves (GWs) significantly regulates the Martian middle‐upper atmospheric dynamics. Thus, these waves influence the transport of tracers and escape in the thermosphere. However, models assume that the non‐orographic GWs are emitted from a constant source level that approximates the averaged Planetary Boundary Layer (PBL). We move on to impose that the emission of the waves follows the top of a real‐time evaluated PBL to account for the diurnal cycle of the waves' source altitudes and implement this improvement in the Mars Planetary Climate Model (Mars PCM). In the absence of the PBL during the night, the non‐orographic GWs are assumed to be launched at altitudes near the surface following Hinson and Wilson (2023, https://doi.org/10.1016/j.icarus.2022.115420 )'s results. Sensitivity tests with the Mars PCM show that non‐orographic GWs are built up efficiently during the (polar) night. With the new scheme, the angular momentum in the upper atmosphere is enhanced. Additionally, simulations recover the “cold pockets” in temperature observed by the Mars Climate Sounder at 80–100 km and capture “deep drops” of the atmospheric species recorded by the Neutral Gas and Ion Mass Spectrometer in the polar night.

Context. Constraining the chemical structure of exoplanetary atmospheres is pivotal for interpreting spectroscopic data and understanding planetary evolution. Traditional retrieval methods often assume thermochemical equilibrium or free profiles, which may fail to capture disequilibrium processes such as photodissociation and vertical mixing. This study leverages the TauREx 3.1 retrieval framework coupled with FRECKLL, a disequilibrium chemistry model, to address these challenges. Aims. The study aims to (1) assess the impact of disequilibrium chemistry on constraining metallicity and C/O ratios; (2) evaluate the role of refractory species (TiO and VO) in spectral retrievals; (3) explore consistency between transit and eclipse observations for temperature and chemical profiles; and (4) determine the effects of retrieval priors and data reduction methods. Methods. Ten hot-Jupiter atmospheres were re-analysed using Hubble Space Telescope (HST) WFC3 data in eclipse and transit. The TauREx-FRECKLL model incorporated disequilibrium chemistry calculations with a Bayesian framework to infer atmospheric properties. Retrieval scenarios included tests with and without TiO and/or VO and comparisons across different data reduction pipelines. Results. The disequilibrium approach significantly alters retrieved metallicity and C/O compared to equilibrium models, impacting insights into planet formation. TiO and/or VO additions improve fits for only two planets, with limited effect on parameter convergence. Retrievals reconcile transit and eclipse temperature profiles in deeper atmospheric layers but not in upper layers. These results are highly dependent on spectral resolution and retrieval priors, emphasising the limitations of HST data and the need for broader spectral coverage from instruments such as JWST. Conclusions. This study demonstrates the feasibility and importance of incorporating disequilibrium chemistry in atmospheric retrievals, highlighting its potential for advancing our understanding of exoplanetary atmospheres with next-generation telescopes.

Context. Before JWST, telescope observations were not sensitive enough to constrain the nature of clouds in exo-atmospheres. Recent observations, however, have inferred cloud signatures as well as haze-enhanced scattering slopes motivating the need for modern inversion techniques and a deeper understanding of the JWST information content. Aims. We aim to investigate the information content of JWST exoplanet spectra. We particularly focus on designing an inversion technique able to handle a wide range of cloud and hazes. Methods. We built a flexible aerosol parameterization within the T AU RE X framework, enabling us to conduct atmospheric retrievals of planetary atmospheres. The method is evaluated on available Cassini occultations of Titan. We then use the model to interpret the recent JWST data for the prototypical hot Jupiters HAT-P-18 b, WASP-39 b, WASP-96 b, and WASP-107 b. In parallel, we performed complementary simulations on controlled scenarios to further understand the information content of JWST data and provide parameterization guidelines. Results. Our results use free and kinetic chemistry retrievals to extract the main atmospheric properties of key JWST exoplanets, including their main molecular abundances (and elemental ratios), thermal structures, and aerosol properties. In our investigations, we show the need for a wide wavelength coverage to robustly characterize clouds and hazes - which is necessary to mitigate biases arising from our lack of priors on their composition - and break degeneracies with atmospheric chemical composition. With JWST, the characterization of clouds and hazes might be difficult, due to the lack of simultaneous wavelength coverage from visible to mid-infrared by a single instrument and the likely presence of temporal variability between visits (from e.g., observing conditions, instrument systematics, stellar host variability, or planetary weather).

In the Martian atmosphere, carbon dioxide (CO2) clouds have been revealed by numerous instruments around Mars from the beginning of the XXI century. These observed clouds can be distinguished by two kinds involving different formation processes: those formed during the winter in polar regions located in the troposphere, and those formed during the Martian year at low- and mid-northern latitudes located in the mesosphere (Määattänen et al, 2013). Microphysical processes of the formation of these clouds are still not fully understood. However, modeling studies revealed processes necessary for their formation: the requirement of waves that perturb the atmosphere leading to a temperature below the condensation of CO2 (transient planetary waves for tropospheric clouds (Kuroda et al., 20123), thermal tides (Gonzalez-Galindo et al., 2011) and gravity waves for mesospheric clouds (Spiga et al., 2012)). In the last decade, a state-of-the-art microphysical column (1D) model for CO2 clouds in a Martian atmosphere was developed at Laboratoire Atmosphères, Observations Spatiales (LATMOS) (Listowski et al., 2013, 2014). We use our full microphysical model of CO2 cloud formation to investigate the occurrence of these CO2 clouds by coupling it with the Global Climate Model (GCM) of the Laboratoire de Météorologie Dynamique (LMD) (Forget et al., 1999). We recently activated the radiative impact of CO2 clouds in the atmosphere. Last modeling results on Martian CO2 clouds properties and their impacts on the atmosphere will be presented and be compared to observational data.

To address questions about the driving mechanisms of Saturn's equatorial oscillation, our team at the Laboratoire de Météorologie Dynamique built the DYNAMICO-Saturn Global Climate Model to study tropospheric dynamics, tropospheric waves activity (Spiga et al. 2020) and equatorial stratospheric dynamics (Bardet et al. 2020) of Saturn. Previous studies (Guerlet et al. 2014, Spiga et al. 2020, Cabanes et al. 2020) have shown that our model produces consistent thermal structure and seasonal variability compared to Cassini CIRS measurements, mid-latitude eddy-driven tropospheric eastward and westward jets commensurate to those observed and following the zonostrophic regime, and planetary-scale waves such as Rossby-gravity (Yanai), Rossby and Kelvin waves in the tropical channel. Extending the model top toward the upper stratosphere allowed our model to produce an almost semi-annual equatorial oscillation with opposite eastward and westward phases. Associated temperature anomalies have a similar behavior than the Cassini/CIRS observations, but the amplitude of the temperature oscillation is twice smaller than the observed one. The absence of sub-grid-scale waves in the model produces an imbalance in eastward- and westward-wave forcing on the mean flow and could be an explanation to the irregularity in both the oscillating period and the downward rate propagation of the resolved Saturn equatorial oscillation.To explore the impact of those small-scale waves on the spontaneous equatorial oscillation emerging in the DYNAMICO-Saturn GCM (Bardet et al. 2020), we add a sub-grid-scale non-orographic gravity waves drag parameterization in our model.This parameterization is directly adapted from the stochastic terrestrial model of Lott et al. (2012). This formalism represents a broadband gravity wave spectrum, using the superposition of a large statistical set of monochromatic waves. As the time scale of the life cycles of gravity waves is much longer than the time step of our GCM, our parametrization can launch a few waves whose characteristics are randomly chosen at each time step. This stochastic gravity waves drag parameterization is applied in DYNAMICO-Saturn on all points of the horizontal grid.A key parameter used in the non-orographic gravity waves drag parameterization is the maximum value of the Eliassen-Palm flux. The Eliassen Palm flux represents the momentum carried by waves that could be transferred to the mean flow. This value has never been measured in Saturn's atmosphere and it represents an important degree of freedom in the parameterization of gravity waves.We performed several test simulations, lasting two Saturn years whose initial state is derived from Bardet et al (2020), with an horizontal resolution of 1/2° in longitude/latitude and a vertical resolution ranging between 3 bar to 1 μbar. For these test simulations, the maximum value of the Eliassen-Palm fulx is set to 10-6, 10-5, 10-4 and 10-3 kg m-1 s-2. Preliminary results show that the appropriate value of our main parameter is between 10-5 and 10-4 kg m-1 s-2. Eliassen-Palm flux value of 10-3 kg m-1 s-2 demonstrates a too large impact: the equatorial oscillation is entirely vanished is this configuration. The simulation using the value of 10-6 kg m-1 s-2 is equivalent to the control simulation without the gravity waves drag parameterization. The next step is to test other parameters, as phase velocity of the gravity waves, horizontal wavenumber, to understand how gravity waves impact the equatorial oscillation.

Located at an average distance of 19 AU and 30 AU respectively from the sun, Uranus and Neptune are mysterious and hard-to-reach worlds. These two planets are characterized by low sunshine and long orbital periods and by very marked seasonal variations (especially for Uranus). Today, Voyager 2 is the only probe to have made a flyby of these two planets and it has revealed that these cold worlds have an intense atmospheric circulation [1,2]. Since then, other zonal wind measurements using cloud tracking have been carried out with the aid of Hubble Space Telescope and terrestrial observatories like the Keck observatory or the Very Large Telescope (see review by [3] and references therein). These measurements confirm and complement previous Voyager 2 observations: zonal flow over these planets is characterized by two prograde jets at mid-latitudes as well as a large retrograde jet at the equator. While the amplitude of the prograde jets is similar on the two planets (250 m/s on Uranus, 275 m/s on Neptune), that of the equatorial retrograde jet is different: it is -50 m/s on Uranus but reaches -400 m/s on Neptune.Understanding the origin of these jets is one of the major current challenges in physics of planetary atmospheres. Furthermore, the impact of Uranus and Neptune different radiative forcings on their atmospheric circulation remains to be assessed. The weath of observations has motivated the need to develop models in order to better interpret these observations and to understand the processes that govern their atmospheric circulation.Several models have attempted to explain the atmospheric circulation visible on the four giant planets. In the case of deep convection models, the equatorial sub-rotation could not be reproduced [4,5,6,7,8] except by greatly modifying the known internal heat flux, which is thus not satisfactory [9,10]. In the case of shallow-flow models, this equatorial sub-rotation could be reproduced if convective Rossby wave generation is weak or absent or baroclinic eddies generation is sufficiently strong [11] or by release of latent heat by the water vapor layer located at 200-300 bars [12]. However, the simulated jet speeds are too slow compared to observations. Furthermore, the radiative transfer was idealized as Newtonian cooling, and seasonal effects were ignored. Here, the objective is to apply a shallow-flow model which takes into account realistic physical parameterizations, to attempt to reproduce this circulation, to answer observational questions but also to determine the dynamical processes governing in these atmospheres.Figure 1: Latitude-pressure cross-section of zonal-mean zonal wind of the third simulated year on Neptune from our preliminary results. A complex zonal structure is present in mid-latitudes and at equator but the zonal structure is still evolving because the radiative-convective equilibrium has still not been reached in the troposphere. Here, the retrograde equatorial stratospheric jet reaches -130 m/s.We introduce the DYNAMICO-giant model which is a General Circulation Model (GCM) developed by the Laboratoire de Météorologie Dynamique (LMD), previously used for the atmospheres of giant planets [13,14,15,16]. The model is composed of a dynamic core which uses an icosahedral grid [17] and which is coupled to independent physical parameterizations such as a radiative transfer or convection. In this study, the radiative transfer module employs the correlated-k formalism. We take into account gaseous opacities from CH4, C2H2 and C2H6 and collision-induced absorption opacities (H2-H2, H2-He, H2-CH4, He-CH4 and CH4-CH4) assuming a H2 ortho/para fraction at equilibrium. Stratospheric aerosols [18] and two cloud layers of CH4 and H2S are also included. Our model accounts for the internal heat flux, for multiple scattering as proposed by [19] and Rayleigh scattering. During this congress, we will discuss the insights gained from GCM simulations at high horizontal resolution (equivalent to 1° in latitude/longitude) on a layer of the atmosphere located between 3 bar and 0.3 mbar and split in 40 vertical levels. The preliminary results obtained from 3 simulated years on Neptune by the GCM make it possible to highlight a complex zonal circulation characterized by an intense retrograde equatorial jet (fig.1) and a strong eddy activity characterized by bursts.First of all, we will present the zonal and meridional circulation obtained after 10 simulated Neptune years, which is the expected spin-up time based on our experience with Saturn and Jupiter. Then, we will compare the thermal structure obtained on our simulations with the observations from [20]. Next, we will discuss the eddy activity highlighted by the diagnostics of the circulation (eddy momentum transport, spectral analysis of waves,...) and finally, its contribution to the acceleration or deceleration of the simulated jets. AcknowledgementsThe authors would like to thank Leigh N. Fletcher and Glenn S. Orton for sending us the zonal mean temperature data on Neptune and Uranus, and Bernard Schmitt for sending us the optical constants of H2S ice. G. Milcareck, S. Guerlet and A. Spiga acknowledge funding from Agence Nationale de la Recherche (ANR) project SOUND, ANR-20-CE49-00009-01.References[1] Lindal et al. (1987). Journal of Geophysics Research, 92.[2] Lindal et al. (1992). Astronomical Journal, 103.[3] Fletcher et al. (2020). Space Science Reviews, 216.[4] Yano et al. (2005). Geophysical and Astrophysical Fluid Dynamics, 99.[5] Heimpel et al. (2005). Nature, 438.[6] Vasavada and Showman (2005). Reports on Progress in Physics, 68.[7] Heimpel and Aurnou (2007). Icarus, 187.[8] Glatzmaier et al. (2009). Geophysical and Astrophysical Fluid Dynamics, 103.[9] Aurnou et al. (2007). Icarus, 190.[10] Soderlund et al. (2013). Icarus, 224.[11] Liu and Schneider (2010). Journal of Atmospheric Sciences, 67.[12] Lian and Showman (2010). Icarus, 207.[13] Guerlet et al. (2014). Icarus, 238.[14] Spiga et al. (2020). Icarus, 335.[15] Cabanes et al. (2020). Icarus, 345.[16] Bardet et al. (2021). Icarus, 354.[17] Dubos et al. (2015). Geoscientific Model Development, 8.[18] Vatant d’Ollone et al. In preparation.[19] Toon et al. (1989). Journal of GeophysicsResearch, 94.[20] Fletcher et al. (2014). Icarus, 231.

Flyby of Uranus and Neptune by Voyager 2 in 1986 and 1989 have shown intense zonal circulation and unexpected meteorological activity. Characterized by a prograde jet at mid-latitude in each hemisphere and a retrograde jet centred on the equator, the zonal structure of the wind is similar on these two planets despite very different seasonal radiative forcing. Understanding atmospheric circulation in gas and ice giant planets, with comparative planetology aspects that could be relevant to the exoplanet community is one of the major current challenges in the physics of planetary atmospheres.To reproduce the zonal jets as well as the strong meteorological activity on Uranus and Neptune, 1° resolution numerical simulations have been performed with a Global Climate Model (GCM) named DYNAMICO Ice Giants Planetary Climate Model. According to our GCM, the zonal wind has a complex structure in altitude on Uranus and Neptune. At the tropopause level (100 hPa), the zonal-mean zonal wind speed averaged over the whole year shows a retrograde jet centred near the equator and a prograde jet at mid-latitudes in each hemisphere on both planets (figure 1 and 2). Although the structure of the jets is qualitatively similar to that observed, the intensity of the jets is much less intense than the values obtained by cloud tracking since the Voyager 2 era. On Neptune, the equatorial retrograde jet observed at -400 m/s only reaches around -50 m/s in our simulations. We also note that the simulated prograde jets are narrower than those observed and that they are incorrectly positioned in latitude. On both planets (particularly Uranus), an equatorial migration of the jets also takes place in our simulations. The low intensity of the simulated jets is very similar to that obtained by previous simulations. This similarity between simulations indicates that one or more forcings are missing from these models. One of the forcings currently under investigation is the tropospheric methane meridional gradient which can influence the zonal wind and the thermal structure.At the same time, we identified an equatorial oscillation on Uranus with a period of one year on average. Temperature anomalies of ~5 to 10 K are observed in connection with this oscillation. On Uranus, the vertical temperature profile obtained looks similar to that obtained from observations at the equator. We identify the local extrema observed on this profile as being possibly the temperature anomalies caused by the equatorial oscillation. The meridional thermal structure at higher latitudes is very different from that obtained with a radiative-convective model. Seasonal variations are greatly attenuated by atmospheric dynamics. The meridional and temporal variations observed on Neptune are qualitatively similar to those simulated by our model. A meridional circulation has been identified using the Transformed (TEM) and Classical Eulerian Mean (CEM) formalism. In the classical case, a circulation very similar to that deduced from the observations has been reproduced on Uranus. It takes the form of a subsidence at the equator and poles and an upwelling at mid-latitudes. But on Neptune, no coherent circulation cell has been identified using this formalism. In the TEM case, only one direct thermal circulation cell is present on each hemisphere for both planets. Figure 1: Vertical cross-section of the zonal-mean zonal wind speed averaged over one year on Uranus. The black lines represent the isotherms. Figure 2: Same as figure 1 but for Neptune.

Aims. The atmosphere of Jupiter is characterized by banded jets, including an equatorial super-rotating jet, by an intense moist con-vective activity, and by perturbations exerted by vortices, waves, and turbulence. Even after space exploration missions to Jupiter and detailed numerical modeling of Jupiter, questions remain about the mechanisms underlying the banded jets and the role played by dry and moist convection in maintaining these jets. Methods. We report three-dimensional simulations of the Jupiter weather layer using a global climate model (GCM) called Jupiter-DYNAMICO, which couples hydrodynamical integrations on an icosahedral grid with detailed radiative transfer computations. We added a thermal plume model for Jupiter that emulates the effect of mixing of heat, momentum, and tracers by dry and moist convec-tive plumes that are left unresolved in the GCM mesh spacing with a physics-based approach. Results. Our Jupiter-DYNAMICO global climate simulations show that the large-scale Jovian flow, in particular the jet structure, could be highly sensitive to the water abundance in the troposphere and that an abundance threshold exists at which equatorial super-rotation develops. In contrast to our dry (or weakly moist) simulations, simulations that include the observed amount of tropospheric water exhibit a clear-cut super-rotating eastward jet at the equator and a dozen eastward mid-latitude jets that do not migrate poleward. The magnitudes agree with the observations. The convective activity simulated by our thermal plume model is weaker in the equatorial regions than in mid to high latitudes, as indicated by lightning observations. Regardless of whether they are dry or moist, our simulations exhibit the observed inverse energy cascade from small (eddies) to large scales (jets) in a zonostrophic regime.

Using images at multiple mid-infrared wavelengths, acquired in May 2018 using the VISIR instrument on ESO's Very Large Telescope (VLT), we study Jupiter's pole-to-pole thermal, chemical and aerosol structure in the troposphere and stratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones and warm cloud-free cyclonic belts persists throughout the mid-latitudes, up to the polar boundaries, and evidence a strong correlation with the vertical maximum windshear and the locations of Jupiter's zonal jets. At high latitudes, VISIR images reveal a large region of mid-infrared cooling poleward $\sim$64$^{\circ}$N and $\sim$67$^{\circ}$S extending from the upper troposphere to the stratosphere, co-located with the reflective aerosols observed by JunoCam, and suggesting that aerosols play a key role in the radiative cooling at the poles. Comparison of zonal-mean thermal properties and high-resolution visible imaging from Juno allows us to study the variability of atmospheric properties as a function of altitude and jet boundaries, particularly in the cold southern polar vortex. However, the southern stratospheric polar vortex is partly masked by a warm mid-infrared signature of the aurora. Co-located with the southern main auroral oval, this warming results from the auroral precipitation and/or joule heating which heat the atmosphere and thus cause a significant stratospheric emission. This high emission results from a large enhancement of both ethane and acetylene in the polar region, reinforcing the evidence of enhanced ion-related chemistry in Jupiter's auroral regions.

A multi-decade record of ground-based mid-infrared (7–25μm) images of Saturn is used to explore seasonal and non-seasonal variability in thermal emission over more than a Saturnian year (1984–2022). Thermal emission measured by 3-m and 8-m-class observatories (notably NASA's Infrared Telescope Facility, Subaru, and ESO's Very Large Telescope) compares favourably with synthetic images based on both Cassini-derived temperature records and the predictions of radiative climate models. We find that 8-m class facilities are capable of resolving thermal contrasts on the scale of Saturn's belts, zones, polar hexagon, and polar cyclones, superimposed onto large-scale seasonal asymmetries. Seasonal changes in brightness temperatures of ∼30 K in the stratosphere and ∼10 K in the upper troposphere are observed, as the northern and southern polar stratospheric vortices (NPSV and SPSV) form in spring and dissipate in autumn. The timings of the first appearance of the warm polar vortices is successfully reproduced by radiative climate models, confirming them to be radiative phenomena, albeit entrained within sharp boundaries influenced by dynamics. Axisymmetric thermal bands (4–5 per hemisphere) display temperature gradients that are strongly correlated with Saturn's zonal winds, indicating winds that decay in strength with altitude from the cloud-tops to the ∼1-mbar level, and implying meridional circulation cells in Saturn's upper troposphere and stratosphere forming the system of cool zones and warm belts. Saturn's thermal structure is largely repeatable from year to year (via comparison of infrared images in 1989 and 2018), with the exception of low-latitudes. Here we find evidence of inter-annual variations because the equatorial banding at 7.9μm is inconsistent with a ∼15-year period for Saturn's equatorial stratospheric oscillation, i.e., it is not strictly semi-annual. Either the oscillation has a longer period closer to ∼20 years, or its progression is naturally variable and interrupted by tropospheric meteorology (e.g., storms). Finally, observations between 2017–2022 extend the legacy of the Cassini mission, revealing the continued warming of the NPSV during northern summer in line with predictions of radiative climate models.

In this paper, the non‐orographic gravity waves (GW) parameterization of the Mars Planetary Climate Model (PCM) previously implemented by Gilli et al. (2020, https://doi.org/10.1029/2018JE005873 ) is revisited and extended to the exobase (∼250 km). The simulations performed with the new scheme correct some known biases in the modeled thermal tide amplitudes and polar warming, improving the agreement with Mars Climate Sounder (MCS) observed thermal structures and tides below ∼100 km. Additionally, we find that the simulated densities above 150 km are compatible with NGIMS (Neutral Gas and Ion Mass Spectrometer) measured abundances. Large drag depositions ranging up to >∼950 m s −1 sol −1 are induced at altitude of 90–170 km due to the wave saturation (breaking) and depletion, leading to winds damped to magnitudes of ∼150–225 and ∼80 m s −1 in the zonal and meridional directions, respectively. Resulting temperature variations are ∼±10–30 K or 5%–10% at most latitudes except in the polar regions (where they can reach ∼±30–60 K). The results indicate that non‐orographic GW play a significant role in the dynamics of the middle‐upper atmosphere of Mars via the induced transfer of momentum and energy from the lower atmosphere.

The Very Large Telescope Imager and Spectrometer (VISIR) instrument on ESO's Very Large Telescope (VLT) has been used to support the NASA's Juno mission since 2016. The present dataset was collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 0101.C-0073(A)). The 2018 May 24th-27th dataset provides a comprehensive view of Jupiter's pole-to-pole thermal, chemical, and aerosol structure ; including the Great Red Spot; and the auroral-related heating in the southern polar stratosphere; after retrieval calculations. Here, we provide the destriped, cleaned, calibrated and projected data of 2018 May 24h to 27th dataset. For the 7.9µm filter, we have added the radial Doppler velocities files.

<p><strong data-stringify-type="bold">Abstract</strong></p> <p>The Saturn DYNAMICO Global Climate Model (GCM) is a high-resolution, multi-annual numerical simulation of Saturn's atmospheric dynamics [1], combining a radiative-convective equilibrium model [2] and a hydrodynamical solver on an icosahedral grid. The model reproduces well the observed behaviour of jets and eddy-momentum transfer to the mean flow. Vortices arise naturally in the model over time but until now they have not been given direct consideration. Here we investigate the long-term statistical distribution and organization of vortices using (1) a manual visual inspection method and (2) automated techniques that utilise machine learning and analytical calculations as a means of validating the first approach.</p> <p><strong data-stringify-type="bold">Manual Detection</strong></p> <p>This vortex detection method is similar to previous observational studies of Jupiter and Saturn [3, 4, 5, 6] and shows how the spatial and temporal distributions of the modelled vortices compares to those observed on Saturn [4, 5, 6], as well as studying the formation conditions and long-term temporal evolution of vortex distributions. With seven simulated model years at ½-degree spatial resolution, we constrain well the size and location of vortices, the horizontal wind field components and the magnitude and sign of horizontal vorticity, enabling direct comparison of the manual and automated methodologies.</p> <p><strong data-stringify-type="bold">Automated Detection</strong></p> <p>A convolutional neural network is used to reproduce the manual visual detection method across the entire timeseries using the same assumptions and using the results of the manual study as a training set. We also study the Angular Momentum Eddy Detection Algorithm (AMEDA, [7]) designed for the analysis of terrestrial oceanic eddies. The machine learning study is ongoing and the results of the AMEDA algorithm are largely consistent with the manual approach, meaning that this algorithm can be used in future studies of Jupiter and Saturn DYNAMICO GCM outputs.</p> <p><img src="" /></p> <p>Figure 1: Vortex count over the entire mature model timeline for the manual (black) and AMEDA (red) approaches. Manual technique measures at each seasonal peak, AMEDA measures at each timestep to create a seasonal average for comparison. AMEDA analysis to be extended to earlier years.</p> <p><img src="" /></p> <p>Figure 2: Vortex east-west size (left), north-south size (centre) and shape (right), in units of 10<sup>3</sup>km, for the manual (top) and AMEDA (bottom) approaches.</p> <p><img src="" /></p> <p>Figure 3: Overall distribution of vortices for entire timeseries with the manual (left subplot) and AMEDA (right subplot) approaches. In each subplot: (Left) histogram of total vortex count. (Centre) instantaneous zonal wind speed at the vortex centre with the mean zonal wind profile. (Right) vortex average size and vorticity sign.</p> <p> </p> <p><img src="" /></p> <p>Figure 4: (Top) Maximum tangential velocity at vortex edge as a function of distance from the vortex centre (scatter), derived from the AMEDA approach, alongside the geostrophic balance condition (black straight line), all vortices are subgeostrophic. (Bottom) the ratio of vortex V<sub>max</sub> and the geostrophic condition as a measure of "vortex geostrophy", with respect to latitude, smaller and higher-latitude vortices tend to be clsoer to the geostrophic condition.</p> <p><strong data-stringify-type="bold">Acknowledgements</strong></p> <p>Donnelly and the France authors were supported by Agence Nationale de la Recherche (ANR) and the UK authors acknowledge the Science and Technology Facilities Council (STFC, James) and the European Research Council (ERC, Bardet).</p> <p>References</p> <p>[1] Spiga et al. (2020), Icarus, 335, http://dx.doi.org/10.1016/j.icarus.2019.07.011.</p> <p>[2] Guerlet et al. (2014), Icarus, 238, https://doi.org/10.1016/j.icarus.2014.05.010.</p> <p>[3] Li et al. (2004), Icarus, 172, https://doi.org/10.1016/j.icarus.2003.10.015.</p> <p>[4] Vasavada et al. (2006), J. Geophys. Res. Planets, 111, https://doi.org/10.1029/2005JE002563.</p> <p>[5] Trammell et al. (2014), Icarus, 242, https://doi.org/10.1016/j.icarus.2014.07.019.</p> <p>[6] Trammell et al. (2016), J. Geophys. Res. Planets, 121, https://doi.org/10.1002/2016JE005122.</p> <p>[7] Le Vu et al. (2018), J. Atmos. Ocean. Tech., 35, https://doi.org/10.1175/JTECH-D-17-0010.1</p>

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.

In this talk, we present highlights from our recent analyses of mid-infrared observations of Uranus and Neptune, and we look ahead to anticipated discoveries from the James Webb Space Telescope. Drawing from a combination of archival and recent ground-based imaging and spectroscopy, we examine the spatial structure and trends of mid-infrared emission from the ice giant atmospheres. We report on surprising temporal variability in the atmosphere of Neptune (see Figure 1) with an unexpected decline in stratospheric temperatures since at least 2003. Recent VLT-VISIR imaging and spectroscopy are presented, revealing how this trend has progressed. In contrast, we show that no evidence yet exists of long-term thermal changes in Uranus’ stratosphere, but mid-IR observations of Uranus are still extremely limited. The observed spatial structure of Uranus’ mid-infrared emission is intriguing (Figure 2), as it is inconsistent with simple models of the atmospheric circulation and/or chemistry and its physical interpretation remains unclear. We share recent observations from VLT-VISIR and express the need for continued ground-based imaging for both Uranus and Neptune. Finally, we discuss how the James Webb Space Telescope MIRI observations will help greatly advance our understanding of the ice giants in the years ahead. In particular, given its supreme sensitivity compared to ground-based observations, JWST-MIRI observations will resolve the nature of Uranus stratospheric thermal/chemical structure and reveal how temperature and chemical abundances change with the seasons in the atmospheres of both ice giants. Figure 1: Observed changes in Neptune’s thermal-infrared brightness, a measure of temperature in Neptune’s atmosphere. The plot shows the relative change in the thermal-infrared brightness from Neptune’s stratosphere with time for all existing images taken by ground-based telescopes. Brighter images are interpreted as warmer. Corresponding thermal-infrared images (top) at wavelengths of ~12 µm show Neptune’s appearance in 2006, 2009, 2018 (observed by the European Southern Observatory’s Very Large Telescope VISIR instrument), and 2020 (observed by Subaru’s COMICS instrument). The south pole appears to have become dramatically warmer in just the past few years. Figure 2: Uranus' 13-micron images from VLT-VISIR in 2009 and 2018, with enhanced emission from high latitudes. From current ground-based observations alone, it is unclear whether the enhanced radiances are due to greater temperatures or enhance acetylene abundances, but JWST will solve this mystery.

Planetary stratospheres are characterized by a subtle interplay between dynamics, radiation and chemistry. Observations of Saturn's stratosphere have revealed a semi-annual equatorial oscillation of temperature and hinted at an interhemispheric circulation of hydrocarbon species. Both the forcing mechanisms of the former and the existence of the latter have remained debated. Here we use a new troposphere-to-stratosphere Saturn global climate model to argue that those two open questions are intimately connected. Our Saturn climate model reproduces a stratospheric oscillation exhibiting the observed semi-annual period, amplitude and downward propagation. In the same Saturn simulation, a prominent stratospheric summer-to-winter hemispheric circulation develops at the solstices, controlled by both the seasonal radiative gradients and Rossby-wave pumping in the winter-subsiding branch, analogous to Earth's Brewer–Dobson circulation. Furthermore, we show that Saturn's equatorial oscillation is driven by the seasonal variability of both the resolved planetary-scale wave activity and the interhemispheric circulation, akin to Earth's Semi-Annual oscillation. A high-resolution three-dimensional global climate model of Saturn captures the small-scale dynamics of its stratosphere. It is able to reproduce the observed semi-annual equatorial oscillation and finds evidence of an interhemispheric meridional circulation that can explain the periodicity of its equatorial oscillation and the seasonal behaviour of hydrocarbon abundances.