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Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) observations spanning 2015 to 2021 confirm a brightening of Uranus’ north polar hood feature with time. The vertical aerosol model of Irwin et al. (2023) (IRW23), consisting of a deep haze layer based at ~5 bar, a 1 - 2 bar haze layer, and an extended haze rising up from the 1 - 2 bar layer, was applied to retrievals on HST Space Telescope Imaging Spectrograph (HST/STIS) observations (Sromovsky et al., 2014, 2019} revealing a reduction in cloud-top CH4 by an average of 0.19 {plus minus} 0.03% between 40 - 80{degree sign}N between 2012 and 2015. A combination of latitudinal retrievals on the HST/WFC3 & HST/STIS datasets, again employing the IRW23 model, reveal a temporal thickening of the 1 - 2 bar haze layer to be the main cause of the polar hood brightening, finding an average increase of 1.09 {plus minus} 0.08 at 0.8 μm north of ~45{degree sign}N, concurrent with a decrease in the imaginary refractive index spectrum of the 1 - 2 bar haze layer north of ~40{degree sign}N and longwards of ~0.7 μm, and between 60{degree sign}N and 80{degree sign}N at ~0.5 μm. Small contributions to the brightening were found from a thickening of the deep aerosol layer, with an average increase in integrated opacity of 0.6 {plus minus} 0.1 north of 45{degree sign}N between 2012 and 2015, and from the aforementioned decrease in cloud-top CH4 abundance. Our results are consistent with the slowing of a meridional circulation, exhibiting strong subsidence at the poles.

Introduction Continued monitoring of Jupiter during the past four decades from Earth-based observatories, the Hubble Space Telescope, and visiting spacecraft has provided essential insights on Jupiter's belt/zone structure from the upper stratosphere to the deeper levels (~100 bar), allowing us to further our knowledge of Jupiter’s climatology, chemistry, and the coupling between the observed atmospheric dynamics and the unseen deeper levels. Jupiter’s equatorial atmosphere is particularly interesting when investigating the atmospheric dynamics and climatology in the giant planets, as its equatorial temperatures and aerosols display remarkable quasi-periodic oscillations from the stratosphere (~1 mbar, e.g. Leovy et al., 1991, Orton et al., 1991) to below the thick ammonia clouds (5-7 bar, Antuñano et al., 2018, 2020). Ground-Based Observations Our study uses almost four decades of ground-based mid-infrared observations (1983 to 2019) captured at NASA’s Infrared Telescope Facility, the Very Large Telescope and the Subaru Telescope at 8 different wavelengths ranging between 7.9 µm and 24.5 µm, to analyse the long-term variability of upper tropospheric and stratospheric equatorial temperatures and aerosol opacity. Examples of Jupiter images over the three decades are shown in Figure 1. Figure 1. Examples of Jupiter images captured at 8.6 µm, over the three decades. In this study, zonal-mean radiance profiles at different wavelengths are stacked together to form 5-point (7.9 µm, 8.6 µm, 10.7 µm, 18.7 µm and 20.5 µm) and 8-point (same as above plus 13.0 µm, 17.6 µm and 24.5 µm) spectral image cubes between 1983-2019 and 1996-2019, respectively. These spectral image cubes are then inverted using the radiative-transfer and retrieval codes NEMESIS (Irwin et al., 2008) to retrieve stratospheric and tropospheric temperatures and tropospheric aerosol-opacity. Troposphere-Stratosphere Coupling Jupiter’s equatorial stratosphere displays a remarkable periodic oscillation, where a vertical alternating pattern in the zonally-averaged temperature and winds is observed between 3 and 20 mbar, both at the equator and off-equatorial latitudes (±12° latitude, Leovy et al., 1991, Cosentino et al., 2017). In our study, we perform a cross-correlation analysis between the retrieved upper-tropospheric and stratospheric temperatures, revealing the extend of Jupiter’s Equatorial Stratospheric Oscillation (JESO) and showing a potential anticorrelation equatorial stratospheric and upper-tropospheric temperature, hinting to a potential troposphere-stratosphere coupling at Jupiter´s equatorial region. Temperature and Aerosol Variability Jupiter´s Equatorial Zone (EZ) undergoes a rare 7-year cyclic disturbance, where the typically white, NH3 cloud-covered, and cold EZ shows a 5-µm bright, NH3 cloud-free region encircling the planet south of the equator, accompanied by a strong coloration event at visible wavelengths (Antuñano et al., 2018). By analysing the long-term temporal variation of the retrieved tropospheric temperatures and aerosol opacity at these latitudes, our study reveals that the equatorial tropospheric aerosol opacity is not only modulated by the Equatorial Zone disturbances, but also by a wave with half the period of the Equatorial Zone disturbances. Our study also presents a quantitative study of the temporal lag between temperature and aerosol opacity changes at these latitudes.

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.

Ground- and space-based remote sensing, from Voyager, to Galileo, Cassini and Juno, has revealed the existence of circulation cells in the troposphere of Jupiter. These circulation cells, which may be similar to terrestrial Ferrel cells [1], show properties that vary significantly as a function of depth, showing circulations of opposing directions above and below the expected level of the water condensation cloud near 4-6 bar [2]. Moreover, the location of each vertical branch of the Ferrel-like cells are correlated to the Jupiter's temperature belt/zone contrast, suggesting a dynamical and thermal link between winds, temperatures, aerosols, and composition. To provide infrared support for Juno spacecraft observations, we have been observing Jupiter with the VISIR mid-infrared instrument on the Very Large Telescope (VLT) since 2016. We analyse images at multiple wavelengths between 5 and 20 µm to study the thermal, chemical and aerosol structure of Jupiter's belts, zones, and polar domains. In particular, an observing run in May 2018 (conciding with Juno's 13 perijove) provided global coverage of Jupiter in thirteen narrow-band filters. These data sense stratospheric temperature (7.9 µm), tropospheric temperature via the collision-induced hydrogen-helium continuum (13, 17.6, 18.6, 19.5 µm), aerosol opacity (8.6 and 8.9 µm), and the distribution of ammonia gas (10.5, 10.7 and 12.3 µm). These wavelengths primarily sound the upper troposphere at p We confirm that the pattern of cool anticyclonic zones and warm cyclonic belts persists throughout the mid-latitudes, up to the boundary of the polar domains. This implies, via thermal wind balance, the decay of the zonal jets as a function of altitude throughout the upper troposphere. Aerosol opacity is often (but not always) highest in the anticyclonic zones, suggesting condensation of saturated vapours, but we caution that aerosol opacity is not a good proxy for atmospheric circulation on any giant planet. The thermal and compositional gradients derived from the VISIR maps are consistent with those from Voyager and Cassini, but opposite to what would be inferred for the Ferrel-like circulations of the deeper cell of [1], which was suggested by [2] to exist only below the water-cloud layer based on Juno microwave observations. Concerning the Jovian polar regions, the analysis of VISIR imaging shows a large region of mid-infrared cooling poleward ~67˚S, co-located with the reflective aerosols observed in methane-band imaging by JunoCam, suggesting that they play a key role in the radiative cooling at the poles, and that this cooling extends from the upper troposphere into the stratosphere. These VISIR observations also reveal thermal contrasts across polar features, such as numerous cyclonic and anticyclonic vortices, as well as evidence of high-altitude heating by auroral precipitation. 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. To investigate the radiative processes and influence of auroral precipitation on the southern cold vortex, a radiative-convective model tailored for Jupiter's atmosphere [4], with an updated polar aerosol distribution from Juno mission results, will be used to determine the aerosol distribution needed to reproduce the thermal structure of the cold polar vortex of Jupiter. [1] Duer, K., Gavriel, N., Galanti, E., Kaspi, Y., Fletcher, L. N., Guillot, T., Bolton, S. J., Levin, S. M., Atreya, S. K., Grassi, D., Ingersoll, A. P., Li, C., Li, L., Lunine, J. I., Orton, G. S., Oyafuso, F. A., Waite, J. H.: Evidence for Multiple Ferrel-Like Cells on Jupiter, Geophysical Research Letters, 2021. [2] Fletcher, L. N., Oyafuso, F. A., Allison, M., Ingersoll, A., Li, L., Kaspi, Y., Galanti, E., Wong, M. H., Orton, G. S., Duer, K., Zhang, Z., Li, C., Guillot, T., Levin, S. M., Bolton, S: Jupiter's Temperate Belt/Zone Contrasts Revealed at Depth by Juno Microwave Observations, Journal of Geophysical Research: Planets, 2021 [3] Irwin, P. G. J., Teanby, N. A., de Kok, R., Fletcher, L. N., Howett, C. J. A., Tsang, C. C. C., Wilson, C. F., Calcutt, S. B., Nixon, C. A., Parrish, P. D.: The NEMESIS planetary atmosphere radiative transfer and retrieval tool, Journal of Quantitative Spectroscopy & Radiative Transfer, 2008 [4] Guerlet, S., Spiga, A., Delattre, H., Fouchet, T.: Radiative-equilibrium model of Jupiter's atmosphere and application to estimating stratospheric circulations, Icarus, 2020

On May 31, 2020 a short-lived convective storm appeared in one of the small cyclones of Jupiter's South Temperate Belt (STB) at planetographic latitude 30.8S. The outbreak was captured by amateur astronomer Clyde Foster in methane-band images, became widely known as Clyde's Spot, and was imaged at very high resolution by the Junocam instrument on board the Juno mission 2.5 days later. Junocam images showed a white two-lobed cyclonic system with high clouds observed in the methane-band at 890 nm. The storm evolved over a few days to become a dark feature that showed turbulence for months, presented oscillations in its drift rate, and slowly expanded, first into a Folded Filamentary Region (FFR), and later into a turbulent segment of the STB over a timescale of one year. On August 7, 2021, a new storm strikingly similar to Clyde's Spot erupted in a cyclone of the STB. The new storm exhibited first a similar transformation into a turbulent dark feature, and later transformed into a dark cyclone fully formed by January 2022. We compare the evolution into a FFR of Clyde's Spot with the formation of a FFR observed by Voyager 2 in 1979 in the South South Temperate Belt (SSTB) after a convective outburst in a cyclone that also developed a two-lobed shape. We also discuss the contemporaneous evolution of an additional cyclone of the STB, which was similar to the one were Clyde's Spot developed. This cyclone did not exhibit visible internal convective activity, and transformed from pale white in 2019, with low contrast with the environment, to dark red in 2020, and thus, was very similar to the outcome of the second storm. This cyclone became bright again in 2021 after interacting with Oval BA. We present observations of these phenomena obtained by amateur astronomers, ground-based telescopes, Hubble Space Telescope and Junocam. This study reveals that short-lived small storms that are active for only a few days can produce complex longterm changes that extend over much larger areas than those initially covered by the storms. In a second paper [In tilde urrigarro et al., 2022] we use the EPIC numerical model to simulate these storms and study moist convection in closed cyclones. We are very thankful to the large community of amateur observers operating small telescopes that submit their Jupiter observations to databases such as PVOL and ALPO-Japan. We are also grateful to two anonymous reviewers for their comments that improved the clarity of this paper. This work has been supported by Grant PID2019-109467GB-I00 funded by MCIN/AEI/10.13039/501100011033/and by Grupos Gobierno Vasco IT1366-19. PI acknowledges a PhD scholarship from Gobierno Vasco. GSO and TM were supported by NASA with funds distributed to the Jet Propulsion Laboratory, California Institute of Technology under contract 80NM0018D0004. C. J. Hansen was sup-ported by funds from NASA, USA to the Juno mission via the Planetary Science Institute. IOE was supported by a contract funded by Europlanet 2024 RI to navigate Junocam images, now available as maps in PVOL at http://pvol2.ehu.eus. Europlanet 2024 RI has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement No 871149. G.S. Orton, S. R. Brueshaber, T. W. Momary, K. H. Baines and E. K. Dahl were visiting Astronomers at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR19D0030 with the National Aeronautics and Space Administration. In addition, support from NASA Juno Participating Scientist award 80NSSC19K1265 was provided to M.H. Wong. This work has used data acquired from the NASA/ESA Hubble Space Telescope (HST) , which is operated by the Association of 807 Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These HST observations are associated with several HST observing programs: GO/DD 14661 (PI: M.H. Wong) , GO/DD 15665 (PI: I. de Pater) , GO/DD 15159 (PI: M. H. Wong) , GO/DD 15502 (PI: A. Simon) , GO/DD 14661 (PI: M. H. Wong) , GO/DD 16074 (PI: M.H. Wong) , GO/DD 16053 (PI: I. de Pater) , GO/DD 15929 (PI: A. Simon) , GO/DD 16269 (PI: A. Simon) . PlanetCam observations were collected at the Centro Astronomico Hispanico en Andalucia (CAHA) , operated jointly by the Instituto de Astrofisica de Andalucia (CSIC) and the Andalusian Universities (Junta de Andalucia) . This work was enabled by the location of the IRTF and Gemini North telescopes within the Mauakea Science Reserve, adjacent to the summit of Maunakea. We are grateful for the privilege of observing Kaawela (Jupiter) from a place that is unique in both its astronomical quality and its cultural signifi-cance. This research has made use of the USGS Integrated Software for Imagers and Spectrometers (ISIS) . Voyager 2 images were accessed through The PDS Ring-Moon Systems Nodes OPUS search service.

Atmospheric temperature is an important parameter controlled by the outward transport of internal energy and the absorption of solar radiation and auroral heating. It is used widely in models of cloud formation, photochemistry, retrieval of elemental abundances from observations, vertical extrapolation of cloud level winds, and as a boundary condition for interior models. The Galileo probe made very precise in situ measurements of Jupiter’s temperature from the upper atmosphere down to a pressure level of ~22 bars. However, those data correspond to a single location of the probe entry site, which also turned out to be a 5-micron hotspot. Other data covering a wider range of latitude and longitude locations are available from the Voyager radio occultation measurements (Lindal et al. JGR 86, A10, 8721, 1981). The use of S and X bands (2.3 GHz and 8.4 GHz) on Voyager allowed measurements of atmospheric refractivity from approximately 1 millibar to the 1 bar level. However, the temperatures derived from these observations were based on the then-available information on refractivities and composition, which have since been refined. Tabulated data are largely not available and so we have first digitized the data from the published figures of all available Voyager radio occultations and verified their fidelity. We then applied correction factors to the pressures and temperatures based on current laboratory data on radio refractivities of gases relevant to the radio occultation regime (H2, He, CH4, PH3, Ne and Ar) and used the gas abundances measured by the Galileo probe, also accounting for their implied revision of the assumed molecular weight. Depending on the set of radio occultation observations, the corrected temperature is greater by as much as 3 K at the 1-bar level and 6 K at the 1-millibar level compared to the originally published profile (Lindal et al. 1981). Considering all available radio occultation data sets the corrected temperature at the 1-bar level is 168.69±6.13 K, including some allowance for small latitudinal, longitudinal, and temporal variations. That allows for the possibility of a wider temperature range of 163-175 K at the 1-bar level than the commonly assumed value of 166 K from the Galileo probe. The profile itself provides an alternative a priori profile for retrieval of temperatures from remote sensing of thermal emission. Temperature at the 1-bar level is a particularly important reference since it serves as an “anchor” in models for retrieving the atmospheric composition and thus has a potential effect on the derived water abundance. It also broadens the range of acceptable upper boundary temperatures for interior models. The corrected data will also serve as a baseline for the radio occultation of Jupiter observations planned in Juno’s extended mission.

We present the primary results from our recent analyses of mid-infrared observations of Neptune and Uranus from ground-based telescopes, including VLT-VISIR, Subaru-COMICS, and Gemini-TEXES. We discuss our recent discovery that Neptune’s stratospheric temperatures appear to be changing dramatically in just the past few years, following decades of cooling. 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. We share new observations from VLT-VISIR, express the need for continued ground-based imaging, and discuss how the James Webb Space Telescope MIRI observations will help greatly advance our understanding of the Ice Giants in the years ahead.

We present an analysis of all currently available ground-based imaging of Neptune in the mid-infrared. Dating between 2003 and 2020, the images reveal changes in Neptune’s mid-infrared (∼8–25 μm) emission over time in the years surrounding Neptune’s 2005 southern summer solstice. Images sensitive to stratospheric ethane (∼12 μm), methane (∼8 μm), and CH3D (∼9 μm) display significant subseasonal temporal variation on regional and global scales. Comparison with H2 S(1) hydrogen quadrupole (∼17.035 μm) spectra suggests that these changes are primarily related to stratospheric temperature changes. The stratosphere appears to have cooled between 2003 and 2009 across multiple filtered wavelengths, followed by a dramatic warming of the south pole between 2018 and 2020. Conversely, upper-tropospheric temperatures—inferred from ∼17 to 25 μm imaging—appear invariant during this period, except for the south pole, which appeared warmest between 2003 and 2006. We discuss the observed variability in the context of seasonal forcing, tropospheric meteorology, and the solar cycle. Collectively, these data provide the strongest evidence to date that processes produce subseasonal variation on both global and regional scales in Neptune’s stratosphere.

An essential component of planetary climatology is knowledge of the tropospheric temperature field and its variability. Previous studies of Jupiter hinted at periodic behavior that was non-seasonal, as well as dynamical relationships between tropospheric and stratospheric temperatures. However, these observations were made over time frames shorter than Jupiter's orbit or they used sparse sampling. We derived upper-tropospheric (300-mbar) temperatures over 40 years, extending those studies to cover several orbits of Jupiter, revealing unexpected results. Periodicities of 4, 7 8-9 and 10-14 years were discovered that involved different latitude bands and seem disconnected from seasonal changes in solar heating. Anti-correlations of variability in opposite hemispheres were particularly striking at 16, 22 and 30 degrees from the equator. Equatorial temperature variations are also anticorrelated with those 60-70 km above. Such behavior suggests a top-down control of equatorial tropospheric temperatures from stratospheric dynamics. Realistic future global climate models must address the origins of these variations in preparation for their extension to a wider array of gas-giant exoplanets., Comment: Primary file: 16 pages, 5 figures. Supplemental File (attached): 12 pages, 3 figures, 1 table

1. Overview Jupiter's banded structure undergoes remarkable global-scale disturbances that can completely change its appearance from the deep troposphere below the cloud deck (2-7 bar) to the stratosphere (~1 mbar). These events can alter Jupiter's cloud structure, aerosols, and temperature field through mechanisms that are not well understood, and provide relevant insights into Jupiter’s time-variable atmospheric dynamics. Characterizing Jupiter's atmospheric changes in the long-term is crucial to better understand the origin and nature of the planetary scale disturbances, distinguishing between seasonal or mechanical forcing, and enables further investigation of the coupling of Jupiter's belts and zones that could explain the presence of 'Global Upheavals' (Rogers, 1995). In this study, we will describe how Jupiter's temperatures and aerosols vary over long spans of time, from the top NH3 clouds to the stable mid-stratosphere, and we will show that although Jupiter's troposphere and stratosphere exhibit a large number dynamical phenomena, there exists quasi-periodic patterns that may aid in future predictions of planetary-scale changes to the banded structure. 2. Ground-Based Observations Continued monitoring of Jupiter from ground-based observatories from the past 40 years has provided an unprecedented resource for understanding the cyclic/non-cyclic environmental changes in temperature, aerosols, and composition governing Jupiter’s dynamic atmosphere. More recently, ground-based observations have provided essential temporal, spectral and spatial resolution to support observations from the Juno spacecraft. Our study uses ground-based mid-infrared observations captured between 1983 and 2019 at wavelengths between 7.9 µm and 24.5 µm by 7 different instruments: the BOLO-1 (1983-1993), AT-1 (1983-1993), MIRAC (1993-1999), MIRLIN (1996-2003) and MIRSI (2003-2011) instruments mounted at the 3-m NASA Infrared Telescope Facility (IRTF) in Hawai'i; the VISIR (2006-2011, 2016-2018) instrument mounted at the 8-m Very Large Telescope (VLT) in Chile; and the COMICS (2005-2019) instrument on the 8-m Subaru Telescope in Hawai'i. Examples of Jupiter images at different wavelengths are given in Figure 1. Figure 1. Examples of images of Jupiter captured by the MIRSI instrument at 7 different wavelengths. 3. Multi-Year Cycles of Variability As mentioned above, Jupiter’s belts and zones endure dramatic global-scale changes over short-timescales, where belts expand, contract and even entirely disappear in a complex and turbulent way (e.g., Fletcher et al., 2017, doi:10.1002/2017GL073806). The most remarkable examples of this are the South Equatorial Belt (SEB, at 7°-17° S) fading and revival cycles (e.g., Sánchez-Lavega & Gomez, 1996, doi:10.1006/icar.1996.0067; Fletcher et al., 2017, doi:10.1016/j.icarus.2017.01.001), where the typically warm and dark belt at visible wavelengths transforms into a cold, cloud-covered whitish zone in timescales of months, remaining disturbed for years before energetic storms trigger the revival of the belt. A similar ‘revival’ process occurs semi-periodically at the North Temperate Belt (NTB, at 21°-28° N), where energetic convective storms rising from the water layer in the deep troposphere at this belt interact with the background flow producing a new low-albedo band over the southern half of the NTB (e.g., Sánchez-Lavega et al., 2017, doi: 10.1002/2017GL073421). At lower latitudes, the North Equatorial Belt (NEB, at 7°-17° N) is observed to expand northward in time intervals of 3 to 5 years, causing a gradual decrease in reflectivity (darkening) at the neighbouring North Tropical Zone (NTrZ, at 18°-21° N), typically originated from wave-like bulges of materials impinging on the NTrZ (e.g. Rogers, 1995; Fletcher et al., 2017, 10.1002/2017GL073383). Finally, Jupiter’s Equatorial Zone (EZ, within ±7° of the equator) experiences a rare 7-year cyclic disturbance, where the typically white (NH3 cloud-covered) and cold EZ displays a new 5-μm-bright (NH3 cloud-free) band encircling the planet south of the equator, accompanied by a reddish coloration at visible wavelengths (e.g., Antuñano et al., 2018, doi: 10.1029/2018GL080382; Rogers, 1995). In this presentation, we will show zonal-mean brightness temperature maps spanning the period between 1983 and 2019 at 5 different wavelengths (7.9 µm, 8.6 µm, 10.7 µm, 18.7 µm and 20.5 µm) and between 1996 and 2019 at 8 wavelengths (same list plus 13.0 µm, 17.6 µm and 24.5 µm). We will describe the temporal and latitudinal variability of the brightness temperature at each of these wavelengths, looking for potential correlation/anticorrelation between changes at different belts that could help to reveal the processes underpinning the jovian global upheavals. We will also compare changes at different wavelengths to better understand the vertical extent of the global-scale disturbances in Jupiter’s banded structure. 4. Temperature and Aerosol Opacity: Variability Zonal-mean radiance profiles at different wavelengths can be stacked together to form 5-point (7.9 µm, 8.6 µm, 10.7 µm, 18.7 µm and 20.5 µm) spectral image cubes between 1983 and 2019 and 8-point (the same plus 13.0 µm, 17.6 µm, and 24.5 µm) spectral image cubes between 1996 and 2019. These spectral image cubes can then be inverted independently using the radiative-transfer and retrieval code NEMESIS (Irwin et al., 2008, doi:10.1016/j.jqsrt.2007.11.006), to obtain crude estimations of stratospheric temperatures at 10-20 mbar (constrained by the 7.9 µm wavelength), upper-tropospheric (100-300 mbar) and mid-tropospheric (~500 mbar) temperatures (constrained by the 17.6 µm-24.5 µm and 10.7 µm, respectively), and tropospheric aerosol opacity at 400-600 mbar (constrained by the 8.6 µm wavelength). Here, we will show stratospheric and tropospheric temperature and aerosol opacity maps between 1983 and 2019. We will describe the timescales of the variability observed in these maps by presenting a Lomb-Scargle analysis, and we will compare their periodicity to previously reported cyclic activity in Jupiter’s atmosphere, describing how temperature and aerosols vary during the planetary-scale disturbances. We will also compare the periodicity found at different belts, showing an NEB-SEB anticorrelation in the aerosol opacity and mid-tropospheric temperatures, and differences in the temperature field and aerosol opacity between hemispheres will be discussed. Finally, we will reveal a tropospheric-stratospheric coupling associated with Jupiter's Equatorial Stratospheric Oscillation.

The identity of the coloring agent(s) in Jupiter's atmosphere and the exact structure of Jupiter's uppermost cloud deck are yet to be conclusively understood. The Cr\`{e}me Br\^ul\'ee model of Jupiter's tropospheric clouds, originally proposed by Baines et al. (2014) and expanded upon by Sromovsky et al. (2017) and Baines et al. (2019), presumes that the chromophore measured by Carlson et al. (2016) is the singular coloring agent in Jupiter's troposphere. In this work, we test the validity of the Cr\`{e}me Br\^ul\'ee model of Jupiter's uppermost cloud deck using spectra measured during the Juno spacecraft's 5$^{\mathrm{th}}$ perijove pass in March 2017. These data were obtained as part of an international ground-based observing campaign in support of the Juno mission using the NMSU Acousto-optic Imaging Camera (NAIC) at the 3.5-m telescope at Apache Point Observatory in Sunspot, NM. We find that the Cr\`{e}me Br\^ul\'ee model cloud layering scheme can reproduce Jupiter's visible spectrum both with the Carlson et al. (2016) chromophore and with modifications to its imaginary index of refraction spectrum. While the Cr\`{e}me Br\^ul\'ee model provides reasonable results for regions of Jupiter's cloud bands such as the North Equatorial Belt and Equatorial Zone, we find that it is not a safe assumption for unique weather events, such as the 2016-2017 Southern Equatorial Belt outbreak that was captured by our measurements., Comment: 38 pages, 21 figures; Accepted for publication in AAS Planetary Science Journal

Jupiter’s Great Red Spot (GRS), a giant anticyclone, is the largest and longest-lived of all the vortices observed in planetary atmospheres. During its history, the GRS has shrunk to half its size since 1879, and encountered many smaller anticyclones and other dynamical features that might tend to erode it. In 2018-2020, while having a historically small size, its structure and even its survival appeared to be threatened when a series of anticyclones moving in from the east tore off large fragments of the red area and distorted its shape. In this work we report observations of the dynamics of these interactions and show that as a result the GRS increased its internal rotation velocity, maintaining its vorticity but decreasing its visible area, and suffering a transient change in its otherwise steady 90-day oscillation in longitude. From a radiative transfer analysis and numerical simulations of the dynamics we show that the interactions affected the upper cloud tops of the GRS. We argue that the intense vorticity of the GRS, together with its larger size and depth compared to the interacting vortices, guarantees its long lifetime. This work has been supported by the Spanish project AYA2015-65041-P and PID2019-109467GB-I00 (MINECO/ FEDER, UE) and Grupos Gobierno Vasco IT1366-19. PI acknowledges a PhD scholarship from Gobierno Vasco. EGM is Serra Hunter Fellow at UPC. This work used data acquired from the NASA/ESA HST Space Telescope, asso- ciated with OPAL program (PI: Simon, GO13937), and archived by the Space Telescope Science Institute, which is operated by the Association of Universi- ties for Research in Astronomy, Inc., under NASA contract NAS 5–26,555. All maps are available at http://dx.doi. org/10.17909/T9G593. PlanetCam ob- servations were collected at the Centro Astronómico Hispánico en Andalucía (CAHA), operated jointly by the Insti- tuto de Astrofisica de Andalucia (CSIC) and the Andalusian Universities (Junta de Andalucía). EGM, MS, APG, MAC and ASL thankfully acknowledge the computer resources at Mare Nostrum and the technical support provided by Barcelona Supercomputing Center (AECT-2019-2-0006). This research has made use of the USGS Integrated Software for Imagers and Spectrometers (ISIS). We appreciate the contribution from all observers cited in TableS1 for his fundamental contribution to this study with Jupiter images obtained with high dedication and skill. GSO and TM were supported by NASA with funds distributed to the Jet Propulsion Laboratory, California Institute of Technology.

International audience; In this White Paper (part I) we present an analysis of our current knowledge of Ice Giant systems in the light of six key science questions about planetary systems formulated in the ``Planetary Exploration, Horizon 2061'' long-term foresight exercise. We formulate measurement requirements and favored destinations for each of these science questions.

International audience; Starting from the six key science objectives for the exploration of planetary systems presented in part I of this White Paper, and from the corresponding measurement requirements for the future exploration of Ice Giants systems, we build a notional road map for a set of missions to these systems that will address most of these science objectives.

The goal of this white paper is to provide examples where ground-based and space-based observations are combined, and used to obtain understanding or constrain parameters beyond what the separate measurements could yield.

We derive Jupiter's zonal vorticity profile from JunoCam images, with Juno's polar orbit allowing the observation of latitudes that are difficult to observe from Earth or from equatorial flybys. We identify cyclonic local vorticity maxima near 77.9°, 65.6°, 59.3°, 50.9°, 42.4°, and 34.3°S planetocentric at a resolution of ~1°, based on analyzing selected JunoCam image pairs taken during the 16 Juno perijove flybys 15-30. We identify zonal anticyclonic local vorticity maxima near 80.7°, 73.8°, 62.1°, 56.4°, 46.9°, 38.0°, and 30.7°S. These results agree with the known zonal wind profile below 64°S, and reveal novel structure further south, including a prominent cyclonic band centered near 66°S. The anticyclonic vorticity maximum near 73.8°S represents a broad and skewed fluctuating anticyclonic band between ~69.0° and ~76.5°S, and is hence poorly defined. This band may even split temporarily into two or three bands. The cyclonic vorticity maximum near 77.9°S appears to be fairly stable during these flybys, probably representing irregular cyclonic structures in the region. The area between ~82° and 90°S is relatively small and close to the terminator, resulting in poor statistics, but generally shows a strongly cyclonic mean vorticity, representing the well-known circumpolar cyclone cluster.The latitude range between ~30°S and ~85°S was particularly well observed, allowing observation periods lasting several hours. For each considered perijove we selected a pair of images separated by about 30 - 60 minutes. We derived high-passed and contrast-normalized south polar equidistant azimuthal maps of Jupiter's cloud tops. They were used to derive maps of local rotation at a resolution of ~1° latitude by stereo-corresponding Monte-Carlo-distributed and Gauss-weighted round tiles for each image pair considered. Only the rotation portion of the stereo correspondence between tiles was used to sample the vorticity maps. For each image pair, we rendered ~40 vorticity maps with different Monte-Carlo runs. The standard deviation of the resulting statistics provided a criterion to define a valid area of the mean vorticity map. Averaging vorticities along circles centered on the south pole returned a zonal vorticity profile for each of the perijoves considered. Averaging the resulting zonal vorticity profiles built the basis for a discussion of the mean profile.JunoCam also images the northern hemisphere, at higher resolution but with coverage restricted to a briefer time span and smaller area due to the nature of Juno's elliptical orbit, which will restrict our ability to obtain zonal vorticity profiles.

Convective storms on Jupiter usually develop in the cyclonic side of the jets or inside cyclones (Vasavada and Showman, 2005). On 31 May 2020 a convective storm developed inside a small cyclone (3º in longitudinal extent) in the South Temperate Belt at planetographic latitude 30ºS. The storm outbreak was captured by amateur astronomer Clyde Foster becoming widely known as Clyde’s spot. The storm was observed 2.5 days later by JunoCam with images displaying an apparent cyclonic structure with two main lobes and high-clouds observable in the methane absorption band. Analysis of these observations show the storm in a decaying phase with associated weak winds. Observations over the following months combined with prior observations (2 years) obtained by JunoCam, HST, IRTF and amateur observers show the long-term evolution of the cyclone before and after the convective eruption. The short-lived storm made the cyclone to display large changes in morphology and colour but not in its size or latitude, except for small fluctuations around a mean latitude and mean drift rate. Ground-based infrared observations at 5 μm show the region where the vortex was located characterized by a weakly warm radiance several months after the convective outbreak, indicating a relative clearing of clouds and haze. We have used the Explicit Planetary Isentropic-Coordinate (EPIC) numerical model (Dowling et. al., 1998) to simulate the cyclone and the effects of convective storms of different strengths and durations on it. These simulations were partially guided by our previous study of a similar convective storm in a different type of cyclone: an elongated structure known as the STB Ghost at the same latitude in 2018 (Iñurrigarro et. al., 2020). Both storms and cyclones were different in terms of their size, morphology and later evolution, but our simulations suggest that in both cases the convective eruptions were of similar power but with different lifetimes indicating that the energy source is water moist convection. We compare these storms and simulations with a similar convective storm observed in 1979 by Voyager 2 at 38ºS that quickly evolved into a Folded-Filamentary Region and investigate the outcome of convective storms at different latitudes from these simulations.References:Dowling et al., 1998. The Explicit Planetary Isentropic-Coordinate (EPIC) Atmospheric Model, Icarus, 132, 221-238.Iñurrigarro et al., 2020. Observations and numerical modelling of a convective disturbance in a large-scale cyclone in Jupiter’s South Temperate Belt, Icarus, 336, 113475.Vasavada and Showman, 2005. Jovian atmospheric dynamics: an update after Galileo and Cassini, Reports on Progress in Physics, 68, 1935-1996.

Observations of thermal emission from Uranus and Neptune have been made over a broad wavelength range from ground-based platforms, airborne observatories, Earth-proximal spacecraft and from the Voyager-2 flybys in the 1980s. Observations since the Voyager flybys have included long-wavelength observations of disk-averaged radiances from the Infrared Space Observatory and the Herschel Space Observatory covering the far-infrared to millimeter range. We present recent airborne spectra from SOFIA covering 17-35 µm, together with Akari and Spitzer spectroscopy at wavelengths extending down to 7 µm, below which contributions from reflected sunlight and potential auroral emissions may confuse the signature of thermal emission. We also show how these disk-averaged spectra are complemented by ground-based filtered imaging and spectroscopy at 8-10m telescopes, which have enabled spatially resolved measurements, complementing those of Voyager IRIS from several decades ago. The critical insights into the structure, chemistry and dynamics of the atmospheres of these Ice Giants attest to the need for significant parts of this spectral region to be included in the instrument complement to be assigned to spacecraft sent to these planets. A vigorous program of Earth-based observations in the accessible spectral range should accompany the spacecraft capability in order to track potential seasonal and non-seasonal variability of these planets, as is evident in the atmospheres of both Jupiter and Saturn. The latter would include mid-infrared observations from the James Webb Space Telescope.

JunoCam, the visible imager on the Juno mission’s payload that was designed primarily for public-outreach purposes, continues to produce images of Jupiter that provide unexpected scientific benefits. Juno’s polar orbits enable observing regions of the planet that have not previously been detected at such high resolution by any previous spacecraft. JunoCam has a single CCD detector with an integral color-strip filter that enables the instrument to image in four color bands—blue, green, red and an 889-nm methane band. JunoCam maps a field of view of 58° across the width of the detector, perpendicular to the spacecraft scan direction. We will describe characteristics and likely origins of bright white compact (~50 km) clouds, informally dubbed “pop-up” clouds by the JunoCam team. We used the length of shadows of these and other features to determine the relative heights of clouds and assigned a provisional chemical classification based on relative altitudes from equilibrium-chemistry predictions. We tracked the continued interactions of small anticyclonic ovals with Jupiter’s Great Red Spot (GRS) that drew off high-altitude reddish haze into strips (commonly called “flakes”) on its western edge. A lightning flash was detected in one of the compact circumpolar cyclones in late December. Observations of the south-polar circumpolar cyclones showed that the original unequally sided pentagon becoming a hexagon – with a cyclone filling in an open area, then a pentagon again over the course of 110 days. In a collaboration with amateur astronomer Clyde Foster (S. Africa), we observed the morphology of an unexpected upwelling in late May of 2020, now known as “Clyde’s Spot”, and tracked its evolution in concert with several ground-based observations. We also measured ~40-50 m/s winds around the sinuous jet bounding the South Polar Hood, an upper-level haze generated by auroral-related chemistry. Lightly processed and raw JunoCam data continue to be posted on the JunoCam webpage at https://missionjuno.swri.edu/junocam/processing. Citizen scientists download these images and upload their processed contributions.

NASA's Spitzer Infrared Spectrometer (IRS) acquired mid-infrared (5-37 microns) disc-averaged spectra of Uranus very near to its equinox in December 2007. A mean spectrum was constructed from observations of multiple central meridian longitudes, spaced equally around the planet, which has provided the opportunity for the most comprehensive globally-averaged characterisation of Uranus' temperature and composition ever obtained (Orton et al., 2014 a [arXiv:1407.2120], b [arXiv:1407.2118]). In this work we analyse the disc-averaged spectra at four separate central meridian longitudes to reveal significant longitudinal variability in thermal emission occurring in Uranus' stratosphere during the 2007 equinox. We detect a variability of up to 15% at wavelengths sensitive to stratospheric methane, ethane and acetylene at the ~0.1-mbar level. The tropospheric hydrogen-helium continuum and deuterated methane absorption exhibit a negligible variation (less than 2%), constraining the phenomenon to the stratosphere. Building on the forward-modelling analysis of the global average study, we present full optimal estimation inversions (using the NEMESIS retrieval algorithm, Irwin et al., 2008 [10.1016/j.jqsrt.2007.11.006]) of the Uranus-2007 spectra at each longitude to distinguish between thermal and compositional variability. We found that the variations can be explained by a temperature change of less than 3 K in the stratosphere. Near-infrared observations from Keck II NIRC2 in December 2007 (Sromovsky et al., 2009 [arXiv:1503.01957], de Pater et al., 2011 [10.1016/j.icarus.2011.06.022]), and mid-infrared observations from VLT/VISIR in 2009 (Roman et al., 2020 [arXiv:1911.12830]), help to localise the potential sources to either large scale uplift or stratospheric wave phenomena., 26 pages, 21 figures, to be published in Icarus (accepted 2021-04-27)

The equatorial stratospheres of Earth, Jupiter and Saturn all exhibit a remarkable periodic oscillation of their temperatures and winds with height. Earth’s quasi-biennial oscillation and Saturn’s quasi-periodic equatorial oscillation have recently been observed to experience disruptions in their vertical structure as a consequence of atmospheric events occurring far from the equator. Here we reveal that Jupiter’s quasi-quadrennial oscillation can also be perturbed by strong tropospheric activity at equatorial and off-equatorial latitudes. Observations of Jupiter’s stratospheric temperatures between 1980 and 2011 show two significantly different periods for the quasi-quadrennial oscillation, with a 5.7-yr period between 1980 and 1990 and a 3.9-yr period between 1996 and 2006. Major disruptions to the predicted quasi-quadrennial oscillation pattern in 1992 and 2007 coincided with marked planetary-scale disturbances in the equatorial and low-latitude troposphere, suggesting that they are connected to vertically propagating waves generated by meteorological sources in the deeper troposphere (that is 500–4,000-mbar pressures). Disruptions in Jupiter’s periodic oscillations are thus inherently different from those of Saturn or the Earth. This interconnectivity between the troposphere and stratosphere, which is probably common to all planetary atmospheres, shows that seemingly regular cycles of variability can switch between different modes when subjected to extreme meteorological events. Multi-decade observations of Jupiter’s stratospheric temperatures show that their quasiperiodic oscillation locked into a new period after a major atmospheric perturbation in 1992, from 5.7 years to 3.9 years. This is different from Earth (and presumably from Saturn), where the period returned to its original value after substantial atmospheric disruptions.

Juno Microwave Radiometer (MWR) observations of Jupiter's mid-latitudes reveal a strong correlation between brightness temperature contrasts and zonal winds, confirming that the banded structure extends throughout the troposphere. However, the microwave brightness gradient is observed to change sign with depth: the belts are microwave-bright in the $p10$ bar range. The transition level (which we call the jovicline) is evident in the MWR 11.5 cm channel, which samples the 5-14 bar range when using the limb-darkening at all emission angles. The transition is located between 4 and 10 bars, and implies that belts change with depth from being NH$_3$-depleted to NH$_3$-enriched, or from physically-warm to physically-cool, or more likely a combination of both. The change in character occurs near the statically stable layer associated with water condensation. The implications of the transition are discussed in terms of ammonia redistribution via meridional circulation cells with opposing flows above and below the water condensation layer, and in terms of the `mushball' precipitation model, which predicts steeper vertical ammonia gradients in the belts versus the zones. We show via the moist thermal wind equation that both the temperature and ammonia interpretations can lead to vertical shear on the zonal winds, but the shear is $\sim50\times$ weaker if only NH$_3$ gradients are considered. Conversely, if MWR observations are associated with kinetic temperature gradients then it would produce zonal winds that increase in strength down to the jovicline, consistent with Galileo probe measurements; then decay slowly at higher pressures., Published in JGR: Planets