Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and Polar Vortices with VLT/VISIR

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

Saturn's Seasonal Variability from Four Decades of Ground-Based Mid-Infrared Observations

A multi-decade record of ground-based mid-infrared (7-25 $\mu$m) 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 compares favourably with synthetic images based on both Cassini-derived temperature records and the predictions of radiative climate models. 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 $\sim30$ K in the stratosphere and $\sim10$ 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, and implying meridional circulation cells 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 7.9 $\mu$m is inconsistent with a $\sim15$-year period for Saturn's equatorial stratospheric oscillation, i.e., it is not strictly semi-annual. Finally, observations between 2017-2022 extend the legacy of the Cassini mission, revealing the continued warming of the NPSV during northern summer. [Abr.]Comment: 25 pages, 15 figures, accepted for publication in Icaru

PTDonnelly/ground_based: Codebase for data reduction and retrieval processing for Bardet et al. (2023)

Processing ground-based planetary observations for mapping and retrieva

Joint evolution of equatorial oscillation and interhemispheric circulation in Saturn’s stratosphere

International audiencePlanetary stratospheres are characterized by a subtle interplay between dynamics, radiation, and chemistry. Observations of Saturn's stratosphere revealed a semi-annual equatorial oscillation of temperature and hinted at an inter-hemispheric 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 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 inter-hemispheric circulation, akin to Earth's Semi-Annual Oscillation

Global climate modeling of the Jupiter troposphere and effect of dry and moist convection on jets

International audienceAims. 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

Global climate modelling of Saturn’s atmosphere, Part V: Large-scale vortices

International audienceThis 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 characterize 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</div

The first direct measurement of the saturnian stratospheric winds

International audience&lt;p&gt;Numerous past observations of Saturn&amp;#160;by ground based and space telescopes have monitored&amp;#160;the movements of clouds and derived direct measurements&amp;#160; of tropospheric wind speeds, giving insights into the tropospheric circulation of the planet. The most remarkable feature is a broad and fast&amp;#160; equatorial&amp;#160;prograde jet, reaching 400-450 m/s. Saturn's stratospheric dynamics is less well known. At low latitudes, it is characterized by the thermal signature of an equatorial oscillation: the observed thermal structure implies that there is a strong oscillating vertical shear of the zonal winds throughout the stratosphere, however, wind speeds in this region cannot be measured by cloud-tracking techniques and remain unknown.&lt;/p&gt;&lt;p&gt;The objective of our study is to measure the stratospheric zonal winds&amp;#160;of&amp;#160;Saturn and&amp;#160;unveil&amp;#160;the circulation of this layer by observing it in the submillimeter range&amp;#160;with&amp;#160;the ALMA interferometer.&amp;#160;For this, we observed the spectral&amp;#160;lines&amp;#160;of HCN at 354 GHz and CO at 345 GHz&amp;#160;emitted&amp;#160;from the limb of the planet. The pressure&amp;#160;level&amp;#160;at which we measure&amp;#160;the winds is about 0.2&amp;#160;mbar.&amp;#160;Thanks&amp;#160;to the high spatial and spectral resolution of ALMA observations at 345 GHz,&amp;#160;we measured&amp;#160;the central frequencies of the emission lines in the whole limb,&amp;#160;subtracted&amp;#160;the rigid rotation of the planet,&amp;#160;and thus derived&amp;#160;the Doppler shift due to the atmospheric motions of the probed layer,&amp;#160;i.e.&amp;#160;the stratospheric winds. The method we used in this study was first developed to observe the stratospheric winds in Jupiter (Cavali&amp;#233; et al. 2021).&amp;#160;&lt;/p&gt;&lt;p&gt;Saturn's rings have&amp;#160;limited our wind observations to latitudes&amp;#160;north of&amp;#160;20&amp;#176;S. The zonal winds obtained in the eastern and western&amp;#160;limbs&amp;#160;are&amp;#160;consistent within error bars. We most&amp;#160;noticeably&amp;#160;detected&amp;#160;a very&amp;#160;broad&amp;#160;eastward jet that spreads from 20&amp;#176;S to 20&amp;#176;N with an average speed of&amp;#160;exceeding 250 m/s.&lt;/p&gt

T cell recognition of Mycobacterium tuberculosis peptides presented by HLA-E derived from infected human cells.

HLA-E is a non-conventional MHC Class I molecule that has been recently demonstrated to present pathogen-derived ligands, resulting in the TCR-dependent activation of αβ CD8+ T cells. The goal of this study was to characterize the ligandome displayed by HLA-E following infection with Mycobacterium tuberculosis (Mtb) using an in-depth mass spectrometry approach. Here we identified 28 Mtb ligands derived from 13 different source proteins, including the Esx family of proteins. When tested for activity with CD8+ T cells isolated from sixteen donors, nine of the ligands elicited an IFN-γ response from at least one donor, with fourteen of 16 donors responding to the Rv0634A19-29 peptide. Further evaluation of this immunodominant peptide response confirmed HLA-E restriction and the presence of Rv0634A19-29-reactive CD8+ T cells in the peripheral blood of human donors. The identification of an Mtb HLA-E ligand that is commonly recognized may provide a target for a non-traditional vaccine strategy

A Surface to Exosphere Non‐Orographic Gravity Wave Parameterization for the Mars Planetary Climate Model

International audienceAbstract 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

Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and Polar Vortices With VLT/VISIR

Using images at multiple mid‐infrared wavelengths, acquired in 2018 May using the Very Large Telescope Imager and Spectrometer (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 ∼64°N and ∼67°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.</p