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NASA's Juno spacecraft has been monitoring Jupiter in 53‐day orbits since 2016. Its six‐frequency microwave radiometer (MWR) is designed to measure black body emission from Jupiter over a range of pressures from a few tenths of a bar to several kilobars in order to retrieve details of the planet's atmospheric composition, in particular, its ammonia and water abundances. A key step toward achieving this goal is the determination of the latitudinal dependence of the nadir brightness temperature and limb darkening of Jupiter's thermal emission through a deconvolution of the measured antenna temperatures. We present a formulation of the deconvolution as an optimal estimation problem. It is demonstrated that a quadratic expression is sufficient to model the angular dependence of the thermal emission for the data set used to perform the deconvolution. Validation of the model and results from a subset of orbits favorable for MWR measurements is presented over a range of latitudes that cover up to 60° from the equator. A heuristic algorithm to mitigate the effects of nonthermal emission is also described.

In its 16 years of scientific measurements, the Spitzer Space Telescope performed a number of groundbreaking and key infrared measurements of Solar System objects near and far. In this second of two Review Articles, we describe results from Spitzer observations of asteroids, dust rings and planets that provide new insight into the formation and evolution of our Solar System. The key Spitzer results presented here can be grouped into three broad classes: characterizing the physical properties of asteroids, notably including a large survey of near-Earth objects; detection and characterization of several dust/debris disks in the Solar System; and comprehensive characterization of ice giant (Uranus and Neptune) atmospheres. Many of these observations provide critical foundations for future infrared space-based observations. In the Spitzer Space Telescope’s 16 years of operation, it observed many Solar System objects and environments. In this second Review Article of a pair, Spitzer’s insight into asteroids, dust clouds and rings and the ice giant planets are summarized.

Microwave observations by the Juno spacecraft have shown that, contrary to expectations, the concentration of ammonia is still variable down to pressures of tens of bars in Jupiter. While mid-latitudes show a strong depletion, the equatorial zone of Jupiter has an abundance of ammonia that is high and nearly uniform with depth. In parallel, Juno determined that the Equatorial Zone is peculiar for its absence of lightning, which is otherwise prevalent most everywhere else on the planet. We show that a model accounting for the presence of small-scale convection and water storms originating in Jupiter’s deep atmosphere accounts for the observations. At mid-latitudes, where thunderstorms powered by water condensation are present, ice particles may be lofted high in the atmosphere, in particular into a region located at pressures between 1.1 and 1.5 bar and temperatures between 173K and 188K, where ammonia vapor can dissolve into water ice to form a low-temperature liquid phase containing about 1/3 ammonia and 2/3 water. We estimate that, following the process creating hailstorms on Earth, this liquid phase enhances the growth of hail-like particles that we call ‘mushballs’. Their growth and fall over many scale heights can effectively deplete ammonia, and consequently, water to great depths in Jupiter’s atmosphere. In the Equatorial Zone, the absence of thunderstorms shows that this process is not occurring, implying that small-scale convection can maintain a near homogeneity of this region. We predict that water, which sinks along with ammonia, should also be depleted down to pressures of tens of bars. Except during storms, Jupiter's deep atmosphere should be stabilized by the mean molecular weight gradient created by the increase in abundance of ammonia and water with depth. This new vision of the mechanisms at play, which are both deep and latitude-dependent, has consequences for our understanding of Jupiter’s deep interior and of giant-planet atmospheres in general.

Jupiter’s atmosphere displays some of the most dramatic weather of any planet in our Solar System, with cycles of activity changing the upper tropospheric and stratospheric temperatures, aerosols, and cloud structures through physical processes that are not yet well understood. In the troposphere, Jupiter’s banded structure undergoes dramatic planetary-scale disturbances that can evolve over short timescales changing its appearance completely at a range of altitudes, from the cloud tops (~500 mbar) to the deeper levels (1-4 bar). Some of these tropospheric variations seem to occur randomly, like the impressive fading and revival of the South Equatorial Belt at 7°-17° S (planetocentric latitude), while others follow a periodic pattern, like the North Equatorial Belt expansions at 7°-17° N (with a ~4.5-year periodicity), the Equatorial Zone disturbances (~7-year period) within ±7° of the equator (Antuñano et al. 2018 doi: https://doi.org/10.1029/2018GL080382) and the convective outbreaks at 21° N in the North Temperate Belt (~5-year period) (Antuñano et al., 2019 doi: https://doi.org/10.3847/1538-3881/ab2cd6). In the stratosphere, Jupiter’s equatorial and off-equatorial temperature and winds at 10-20 mbar exhibit a remarkable 4-5-year periodic oscillation with height forced by waves produced from tropospheric meteorological activity at the equatorial latitudes. Here we use almost 40 years (more than 3 jovian years) of ground-based infrared observations captured at NASA’s Infrared Telescope Facility (IRTF), the Very Large Telescope (VLT) and Subaru between 1980 and 2019 in a number of filters spanning from 7.9 to 24.5 µm. These filters sample upper tropospheric and stratospheric temperatures and aerosols via collision-induced hydrogen and helium absorption, and emission from stratospheric hydrocarbons. This long-term time series is used to (i) understand the impact of the previously mentioned tropospheric activity on the periodicity of the stratospheric temperature oscillations, (ii) characterize the long-term variability of Jupiter’s atmosphere at different altitudes in the upper troposphere and stratosphere, and (iii) investigate the long-term thermal, chemical and aerosol changes in Jupiter’s troposphere. In particular, we generate Lomb-Scargle periodograms and apply a Wavelet Transform analysis to our dataset to look for potential periodicities on the brightness temperature variability in different filters and compare them to previously reported cyclic activity at visible wavelengths (sensing the ammonia cloud top at ~500 mbar) and 5 µm (sensing the 1-4 bar pressure level). Finally, a Principal Component Analyses (PCA) is also performed to analyse the correlation of the brightness temperature variations at different belts and zones.

Observations of Neptune, made in 2018 with the Multi Unit Spectroscopic Explorer (MUSE) instrument (in Narrow-Field Adaptive Optics mode) at the Very Large Telescope (VLT) and covering the wavelength range 480 – 930 nm were previously reported by Irwin et al. (Icarus, 311, 2019). Here, these observations have been reanalysed to incorporate more effectively the effects of limb-darkening following a new approach based on the Minnaert limb-darkening model, after Pérez-Hoyos et al. (Icarus, under review, 2020). The 800 – 900 nm region of our observations includes similar strength absorption bands of methane and H2–H2/H2–He collision-induced absorption, which allows changes in cloud-top altitude to be discriminated from methane abundance variations. Splitting the background atmosphere (i.e., away from bright, discrete clouds) into latitude bands, the measured variation of reflectivity with observed zenith angle at each wavelength is fitted with Minnaert limb-darkening coefficients, which can then be used to reconstruct the expected spectrum at any angle that can then be fitted with our retrieval model, NEMESIS (Irwin et al., JQSRT, 109, 2008). We find that this approach: 1) provides much stronger constraints on the cloud structure and methane abundance; 2) makes better use of all the available data and; 3) is more computationally efficient. We find a very similar variation in cloud-top (at ~3 bar) methane mole fraction as previously reported, but with much better characterized errors, and with mole fractions diminishing from ~5% at equatorial latitudes to ~3% in the south polar region. The retrieved latitudinal distribution of cloud-top methane abundance in Neptune's atmosphere can be seen in the figure below, where Neptune's south pole is at bottom left. We show that, although the reduction of methane abundance is well constrained (i.e., reducing by a factor 5/3 from the equator to the south pole), the absolute abundances are not so well determined. This is because the retrieved methane abundance also depends on the assumed background cloud properties, for which a number of different combinations are found to provide equally good fits to the data, but differ in their retrieved methane abundances by ±1%.

AbstractObservations from the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA’s IRTF and the VISIR instrument on the VLT are used to characterize the Saturn’s seasonal changes. Radiative transfer modelling (using NEMESIS [8]) provides the northern hemisphere temperature progression of the atmosphere over 10 years, both during and beyond the Cassini mission. Comparisons between imaging observations taken one Saturn year apart (1989-2018) show the extent of the interannual variability of Saturn’s northern hemisphere climate for the first time.1. IntroductionWith the culmination of Cassini's unprecedented 13-year exploration of the Saturn system in September 2017, and with no future missions currently scheduled to visit the ringed world, the requirement to build upon Cassini's discoveries now falls upon Earth-based observatories. Mid-infrared observations have been used to characterise features such as the extreme temperatures within an enormous storm system in 2011 [1,6], the cyclic variations in temperatures and winds associated with the 'Quasi-Periodic Oscillation' (QPO) in the equatorial stratosphere [2] and the onset of a seasonal warm polar vortex over the northern summer pole [3].Saturn's axial tilt of 27º subjects its atmosphere to seasonal shifts in insolation [4], the effects of which are most significant at the gas giant's poles. The north pole emerged from northern spring equinox in 2009 (planetocentric solar longitude Ls=0º), and northern summer solstice in May 2017 (Ls=90º), providing Earth-based observers with their best visibility of the north polar region since 1987, with its warm central cyclone and long-lived hexagonal wave [5,6].Studying these interconnected phenomena within Saturn's atmosphere (particularly those that evolve with time in a cyclic fashion) requires regular temporal sampling throughout Saturn's long 29.5-year orbit. We present here a showcase of research from the wealth of archived observations from both TEXES and VISIR obtained over the past decade.1.1 Temperature progressionMethane (CH4) is used to determine stratospheric temperatures due to its even distribution across the planet, as well as its well understood emissive behavior. Figure 1 shows the visible changes in the stratospheric and tropospheric conditions as seen by VISIR over 3 years; these images are representative of a range of filters between 7-20 µm, which can be stacked and inverted to derive the 3D temperature distribution in the upper troposphere and stratosphere. Using this technique, we probe changes in the atmospheric 3D temperature distribution across the planet disc in VISIR observations taken from April 2008 (Ls=343º) to July 2018 (Ls=102º); thereby discerning the spatial variability as well as temporal. VISIR observations concurrent with the Cassini/CIRS observations will be used to cross-check the time-series from Cassini, which can be extended beyond the end-of-mission with the newer VISIR observations. These profiles will provide a new measure of long-term temperature variability in the context of an established model.1.2 Interannual VariabilitySpectroscopic maps of the northern summer hemisphere from TEXES instrument on the IRTF collected in September 2018 have provided a unique opportunity, as they were acquired exactly one Saturn year apart from the 1989 observations of Gezari et al, (1989) [7], which were the first ever 2D images of Saturn in the mid-IR. Examining the differences in brightness temperatures and composition will indicate the extent of any interannual variation for Saturn’s northern hemisphere. This study will also provide unique insight into the timescale of the QPO which will be contrasted with a previously suggested biennial cycle [2]. The seasonal temperature progression measured in Section 1.1 also enables us to place this interannual variability in a wider context and provides further opportunity for insightful comparison with the comparatively shorter-term temperature variability.Figure 1: VISIR observations from P95-102 sensing the troposphere (right) and stratosphere (left). Polar warming is evident in the stratosphere; but is considerably smaller than that seen during southern summer and in the historical record of the 1980s. The warm polar hexagon is seen at the north pole, the first such observation from the ground. Work to remove residual striping is ongoing and has been successfully applied to the 2017 images. 2015-16 images have been published by Fletcher et al., 2017 [2].AcknowledgementsThis research is funded by a European Research Council consolidated grant under the European Union’s Horizon 2020 research and innovation program, grant agreement 723890. We would like to thank co-author Mael Es-Sayeh for his significant contribution to this research.References[1] Fletcher et al., 2012, Icarus 221, p560-586[2] Fletcher et al., 2017, Nature Astronomy, 1, p765-770[3] Fletcher et al. 2015, Icarus. 251, 131-153[4] Fletcher et al., 2015, https://arxiv.org/abs/1510.05690[5] Fletcher et al., 2008, Science. 319, 79-81[6] Fouchet et al., 2016, Icarus, 277, p196-214[7] Gezari et al., 1989, Nature, 342, 777–780[8] Irwin et al. 2008, JQSRT 109:1136-1150[9] Orton et al., 2008, Nature 453, p198

Introduction: The locations of Jupiter’s cloud-top east-west jets are relatively constant over time and define the cyclonic belts and their neighbouring anticyclonic zones. Thermal-infrared observations of the upper troposphere reveal cool temperatures, elevated abundances of condensate and disequilibrium gases, and enhanced cloud opacity over the zones, and the opposite over the belts (Gierasch et al., 1986, doi:10.1016/0019-1035(86)90125-9). This distribution implies upwelling motions in zones and subsidence in belts. However, this picture has been called into question by the observed eddy-momentum flux convergence into the eastward jets (and divergence from the westward jets), which suggests a compensating flow in the opposite direction, from belts into zones, which is partially supported by the distribution of lightning at low latitudes (Little et al., 1999, doi:10.1006/icar.1999.6195). It is possible that two different atmospheric regimes exist: a deep regime where eddies are able to drive the zonal flows, and a higher-altitude regime where those zonal flows decay with height. Reconciling this apparent inconsistency remains a key challenge for the understanding of Jupiter’s atmosphere, and Juno observations of the deeper atmosphere shed important light on this issue. Methodology: Juno’s Microwave Radiometer (MWR) examines the vertical structure of Jupiter’s belts and zones below the clouds by sounding in six channels from 1.4 to 50 cm, sensing from the cloud-tops at ~0.7 bar to pressures greater than 300 bar. Initial results (Li et al. 2017, doi:10.1002/2017GL073159) revealed contrasts at depth that bore a potential resemblance to the belt/zone structure in the upper troposphere. We report on progress in our analysis of averaged nadir microwave brightness and its emission-angle dependence from the first two years of Juno’s mission. We investigate the correlation between the meridional gradient of the brightness temperature at all emission angles and the cloud-top zonal winds. These brightness temperature gradients reflect changes in gaseous opacity (e.g., ammonia and water), kinetic temperature, or both. We explore the implications of the contrasts observed between belts and zones as a function of depth sounded by MWR. Preliminary Results: Meridional brightness temperature gradients above the clouds (poN, this is broadly consistent with results from both the Galileo Probe (Atkinson et al., 1998, doi:10.1029/98JE00060) and Cassini cloud-tracking (Li et al., 2006, doi:10.1029/2005JE002556), which suggested that the jet decayed with height from the ~5-bar level to the 0.5-bar level by more than 90 m/s. We will report on our initial exploration of how these correlations change at deeper pressure levels by looking at MWR wavelengths beyond 10 cm, probing well below the expected condensation level of Jupiter’s water clouds. Acknowledgements: Fletcher was supported by a Royal Society Research Fellowship and European Research Council Consolidator Grant (under the European Union's Horizon 2020 research and innovation programme, grant agreement No 723890) at the University of Leicester. Levin, Orton, and Oyafuso were supported by the National Aeronautics and Space Administration through funds distributed to the Jet Propulsion Laboratory, California Institute of Technology.

Introduction Energetic, high altitude eruptions in Jupiter’s atmosphere, which we refer to as outbreaks, are not uncommon in the North and South Equatorial Belts (NEB and SEB) as well as higher latitudes. However, few have been observed in the Temperate regions. An intense methane-bright outbreak in the South Temperate Belt (STB) latitudes was observed by the lead author on 2020 May 31. Although the outbreak, which would become known as “Clyde’s Spot” in the Pro-Am planetary community, faded quite rapidly in methane wavelengths, developments were monitored by the amateur community over the following weeks. The outbreak occurred two days prior to the Juno Perijove 27 flyby, and close Pro-Am collaboration resulted in very high-resolution images of the outbreak being obtained by the JunoCam imager during the flyby. Outbreak detection The outbreak occurred in the southern part of a pre-existing small white spot at 31⁰S, embedded in a pale grey streak, and suspected of being a cyclonic vortex and was detected early on the 31 May. Observations from other amateurs confirmed that the outbreak had occurred within the previous 10 hours. It was only slightly brighter than before in RGB, but extremely bright in the 0.89 micron CH4 absorption band. It remained methane-bright though much weaker over the following rotations, and from June 1 onwards appeared to consist of two (individually unresolved) parts which moved gradually apart up to June 6, mostly in the E-W direction but with slight cyclonic rotation from June 1-3. NASA Juno PJ27 The JunoCam images on June 2 showed Clyde’s spot as an unusual, roughly oval, bright spot in RGB and CH4, with brighter arcs in its E and W ends that were the pair of methane-bright spots in ground-based images. The spot does not show popup clouds but is marked by numerous concentric arcs which could represent gravity waves in the expanding high-level white cloud (A. Casely). Surrounding streaks confirm that it is within a strongly cyclonic vortex, although it may be over-riding those streaks on the S side. Outcome of the outbreak Amateur images from June 2-3, only small spots at the site of the initial eruption. From June 3 to June 13, v-hi-res images showed at least one white spot and one very dark spot; they changed rapidly in detail, possibly with cyclonic motion. No obvious changes have developed outside this site, apart from appearance of thin blue-grey lines close to the STBn and STBs jets for ~13 deg west Clyde’s spot. In methane images, by June 11 the appearance had reverted to a short oblique methane-dark streak with no bright spot, as it was before the eruption. Cycles of STB Structured sectors This spot erupted tens of degrees east of the only large anticyclonic oval in this domain, Oval BA. Small cyclonic spots have repeatedly arisen here in the last 20 years and expand to form structured sectors of the STB, which persist as large cyclonic segments for several years until they catch up with Oval BA from the west side. Although a new structured sector has been anticipated, it was only ground-based images early in 2020 that showed two new features which could be its precursors. One was a small, very dark spot ~40⁰ east of BA, which persists; the other was the faint oblique streak, centred on a tiny white spot, ~80⁰ east of BA. Clyde’s spot erupted in this latter white spot. Therefore, this eruption may be a previously unknown feature of a cyclonic vortex in this transitional location and stage. Although the outbreak was very short-lived, implying similar outbreaks might be occurring unobserved, its occurrence in this location suggests that it was significant. The outbreak in the context of previous outbreaks. The only similar methane-bright outbreaks previously recorded in the cyclonic STB latitudes were in large structured sectors at the end of their life: the so-called STB Remnant in 2010 and the STB Ghost in 2018 [1,2]. These generated rapidly expanding disturbances that converted these long cyclonic circulations into dark turbulent STB segments. In contrast, Clyde’s spot, being in a very compact cyclonic vortex, has remained confined in its immediate vicinity and has not developed further (as of 2020 June 22). Similar plume outbreaks occasionally occur in small but stable cyclonic vortices in the SEB. This was the way in which at least two recent SEB Revivals [2007, 2010] and two mid-SEB outbreaks [1979, 2017] began, and it is possible that they always do so. Conclusion This was a single, very energetic plume eruption within the small cyclonic spot. Over the following days the plume expanded locally, and disturbance continued at the original site, but there is no evidence of substantial wider changes. This contrasts with the results of the similar eruptions within larger circulations, which were rapidly converted into turbulent dark STB segments. Clyde’s spot was a brief event, never conspicuous in visible light, but detected because of frequent monitoring with methane images. It may represent a previously unknown type of eruption in a small cyclonic spot in the early stages of development of a STB structured sector. An update will be provided in the presentation. Figures: ‘Clyde’s spot’ in 889 nm methane band (left) and RGB (right): (Top) initial detection from C.F. on 31 May 2020; (Bottom) closeups from JunoCam on 2 June 2020. References: J. Rogers (2019), ‘Jupiter’s South Temperate Domain, 2015-2018’. https://britastro.org/node/17283. P. Iñurrigarro et al. (2019-20). ‘Observations and numerical modelling of a convective disturbance in a large-scale cyclone in Jupiter’s South Temperate Belt.’ Icarus 336 (2020), paper 113475.

Introduction Many of Juno’s observations use external information to determine their context in space and time for the “snapshots” of usually very limited regions of the planet that it detects in its close approaches (“perijoves”, PJs). This has been the role of the campaign of supporting observations from the professional community, but it has always been bolstered by the near-continuous observations made by the increasingly sophisticated cadre of the world-wide amateur network. This year is one in which this role was particularly apparent. Tracking Activity in Jupiter Among the many areas of interest in Jupiter undergoing changes are the following. Great Red Spot (GRS). Continuing activity follows on from remarkable interaction of small-scale anticyclones transported counter-clockwise inside the GRS Hollow throughout the spring and fall of 2019. These caused arcuate features, commonly called “flakes”, to appear on the western side of the GRS , which were likely to be material swept off the upper portions of the GRS itself [1]. JunoCam continued to record evidence of them during geocentric solar conjunction at PJ23, PJ24 & PJ25, and the amateur community has continued to monitor them in early 2020. We expect that this type of interaction will continue, as it is apparently tied to the secular longitudinal shrinkage of the GRS, with the results distinguishing between different models for the dynamical interactions involved [2,3]. Equatorial Zone Disturbance. The Equatorial Zone (EZ) was predicted to undergo a disturbance based on the cyclic nature of past events [4] with a major disruption of its bright visual and cold 5-µm appearance. Although the disruption of its 5-µm appearance did not happen, the EZ darkened in blue and UV light, and there was an increase in the thickness or altitude of an upper-atmospheric haze [5]. The amateur-observation record shows that a darker shade of its visual appearance is still present as this coloration episode declines. Juno scientists continue to be interested in the EZ to determine whether such events relate to changes in the remarkably deep-seated upwelling of air detected by the Juno Microwave Radiometer as a column of concentrated ammonia gas [6]. So we are interested in changes to the color, either a return to its normally bright appearance or a renewed darkening that might presage a true disruptive event that is simply “late”. Outbursts. Two major outbursts of convective plumes were observed by JunoCam, one in the North Temperate Belt shortly before PJ2 [7] and another in the South Equatorial Belt near PJ4 [8,9] that was associated with lightning detections [10]. Such outbursts are of interest to Juno scientists. Hi-res amateur imaging also synergizes with JunoCam in characterizing smaller outbursts. One notable example, discovered just before this writing by Foster [11], was recorded in detail by JunoCam at PJ27, showing some morphological similarities with the initial development stages of terrestrial tropical storms. Overcoming COVID-19 Disruptions For recent Juno orbits, low-latitude regions are observed at extremely oblique angles except during perijoves when off-Earth pointing of the spacecraft is adopted. These are chosen carefully because they use up fuel that the Juno science team would like to reserve for an extension of the mission. A single orbit in 2020, chosen for such a turn at PJ26 on April 10, turned out to be in the middle of the COVID-19 pandemic when nearly all professional observatories scheduled to provide Juno support were shuttered. Except for two semi-automated observatories and Hubble Space Telescope, whose ground crew were deemed “essential”, it was the amateur community who provided the only information about Jovian variability during this time. This was also true for PJ27 on June 2, when a few more professional observatories opened. Future Prospects We hope for continued support from the amateur community. Scientists on the Juno mission hope to persuade NASA to fund an extension; one candidate scenario could extend out to PJ70 in late 2025. This would not only extend the time line for continued observations of atmospheric evolution but would take advantage of different types of observations not possible during the primary mission, due to orbital geometry. We would hope observations by this community would continue to provide the continuity of atmospheric scrutiny from which we have benefitted so far. References [1] Foster et al. 2020. The Great Red Spot in 2019 and its interaction with retrograding vortices as monitored by the amateur planetary imaging community. https://britastro.org/node/22552 [2] Sanchez-Lavega, et al. 2019. Jupiter’s Great Red spot threatened along 2019 by strong interactions with close anticyclones. Amer. Geophys. Union meeting. P44A-01. [3] Marcus, et al. 2019. On the shedding of flakes by Jupiter’s Great Red Spot: It is not dying. Amer. Geophys. Union meeting. P13B-3505. [4] Antuñano, et al. 2018. Infrared characterisation of Jupiter's equatorial disturbance cycle. Geophys. Res. Lett. 45, 10987-10995. [5] Orton, et al. 2019. Juno and Juno-supporting observations of Jupiter’s 2018-2019 Equatorial Zone disturbance. EPSC-DPS2019-109. [6] Li et al. 2017. The distribution of ammonia on Jupiter from a preliminary inversion of Juno microwave radiometer data. Geophys. Res. Lett. 44, 5317-5325. [7] Sanchez-Lavega et al. 2017. A planetary-scale disturbance in the most intense Jovian atmospheric jet from JunoCam and ground-based observations. Geophys. Research Lett. 44, 4679-4686. [8] de Pater et al. 2019. First ALMA millimeter wavelength maps of Jupiter, with a multi-wavelength study of convection. Astronomical Journal. 158, 139 (17pp). [9] Wong, et al. 2020. High-resolution UV/optical/IR imaging of Jupiter in 2016-2019. Astrophys. J. Suppl. Ser. M. H. Wong, et al. 2020. High-resolution UV/optical/IR imaging of Jupiter in 2016-2019. Astrophys. J. Suppl. Ser. 247:58 (25 pp). [10] Brown et al. 2018. First detection of lightning sferics from Jupiter reveals new insights into the global distribution of moist convection. Nature 558, 87-90. [11] Foster et al. 2020. A rare methane-bright outbreak in Jupiter’s South Temperate domain. EPSC2020.

Above the dynamic clouds in Neptune’s atmosphere, the temperatures and photochemical composition within Neptune’s stratosphere are expected to respond to slowly modulating insolation over decades [1]. With Neptune’s seasons stretching over more than forty years, the entire history of reliable infrared observations resolving the planet’s disk comprises a mere fraction of a season. Yet, as we shall show, within this relatively brief window, observations appear to show changes in emission that would imply that sub-seasonal processes are significantly modifying the chemical and/or thermal structure in Neptune's stratosphere. We present an analysis of the mid-infrared images and spectra of Neptune acquired using the VISIR instrument at the Very Large Telescope (VLT) between 2006 and 2018. Images in Q-band (17.65, 18.72, 19.50 µm) are used to infer upper-tropospheric temperatures (~200 mbar), while Neptune’s stratosphere (~1 mbar) is analyzed using a combination of imaging and spectra sensitive to emission from ethane (12.2 µm), methane (7.9 µm), and the S(1) hydrogen quadrupole (17.03 µm). While we find that temperatures in the upper troposphere show no significant changes in time (remaining consistent with temperatures inferred from 1989 Voyager-IRIS measurements [2, 3]), the stratospheric emission appears to have changed unexpectedly over the past decade. Absolute radiances are uncertain, but relative trends in the spatially resolved emission are robust and show an asymmetric change in brightness temperature of up to ~3 K between and 2006 and 2008. The 2008 trend in emission continued throughout 2009 observations before returning to a relatively more symmetric pattern in 2018 (see Figure 1). Combined with the 2006 H2 S(1) quadrupole data, the observations indicate that the distribution of stratospheric emission observed in 2006 can likely be explained by the stratospheric temperature structure. However, no contemporaneous VLT-VISIR observations of the quadrupole emission were made in subsequent years, and so the nature of the observed changes between 2006 and 2008-2009 are ambiguous–they can potentially be explained by changes in the stratospheric temperatures, changes in the ethane abundances, or changes in both temperature and chemistry. The timing of these changes coincides with an extended maximum in Neptune’s photometric brightness following the 2005 southern summer solstice [4] and a decline in the discrete cloud coverage apparent in HST imaging [5]. Altogether, these observations suggest that Neptune’s stratosphere experiences intra-seasonal changes that may be coupled to dynamical forcing or variable mixing from the troposphere on timescales of years or less. Figure 1. Relative variation in the longitudinally averaged brightness temperatures inferred from 12.2 µm emission (ethane at ~1 mbar) as a function of latitude for observations from 2006 (light green), 2008 (blue), 2009 (dark green) and 2018 (orange). Example images corresponding to these years are shown in the inset. Absolute calibrations are uncertain and show some spread, so relative trends have been normalized to roughly coincide (arbitrarily) at southern latitudes and the planet limbs, with zero here chosen by the mean. These trends show that the stratospheric emission in 2008 and 2009 differed in shape from those observed in 2006 and 2018, possibly indicating a change in stratospheric temperatures or ethane. The red curve shows the trend in stratospheric hydrogen quadrupole emission for 2006 and suggests that the observed trend in 12.2 µm emission in 2006 was likely primarily determined by the temperature structure. [1] Moses, J. I., Fletcher, L. N., Greathouse, T. K., Orton, G. S., & Hue, V. 2018, Icar, 307, 124. [2] Conrath, B.J., Flasar, F.M., Gierasch, P.J., 1991. Thermal structure and dynamics of Neptune’s atmosphere from Voyager measurements. J. Geophys. Res. 96, 18931–18939. [3] Fletcher, Leigh N., et al. "Neptune at summer solstice: zonal mean temperatures from ground-based observations, 2003–2007." Icarus 231 (2014): 146-167. [4] Lockwood, G. W. "Final compilation of photometry of Uranus and Neptune, 1972–2016." Icarus 324 (2019): 77-85. [5] Karkoschka, Erich. "Neptune’s cloud and haze variations 1994–2008 from 500 HST–WFPC2 images." Icarus 215.2 (2011): 759-773.

Comparing JunoCam images with simulation runs of two-dimensional Euler fluids reveals similarities between the morphology of Jupiter's cloud tops and simulated vorticity maps. We present examples of these analogies. They are required to establish conjectures that state these similarities in a more formal way. Introduction and Context JunoCam [1] has been collecting images of Jupiter's cloud tops for almost four years at the time of the submission of this abstract. In examining these images, we realized that two-dimensional simulations of Euler fluids [2] revealed patterns in vorticity fields reminiscent of structures in Jupiter's cloud tops. We pursue this initial observation further. A small collection of analogies between real data and simulations is presented, which inspire formal conjectures describing a correlation between vorticity and cloud features. These initial conjectures result in algorithm candidates that translate cloud morphology into vorticity and can be assessed and further refined on the basis of fluid-dynamical simulations. In a larger-scale context, when two or more JunoCam images cover the same area of Jupiter with a time delay of several minutes, methods similar to stereo correspondence can be applied to retrieve velocity or vorticity field data. Displacements of corresponding areas of the surface between images can be used either to estimate a velocity field directly, or via the stream function component of a Helmholtz decomposition indirectly. Alternatively, measured rotations of surface areas can be used to estimate vorticities. Vorticity data inferred by any of these methods provide a low-resolution context and a reference for a refinement of the vorticity field on the basis of spatially higher-resolved morphological considerations. The presentation will focus on a small survey of JunoCam images together with simulation runs developing structures similar to those observed in the images. This collection of examples is required for the empirical definition of formal conjectures connecting morphology with vorticity. Example Figure 1 shows an excerpt of a map of Jupiter's north polar region during the PJ18 flyby that suggests a simplified model to initialize a simulation run. The initial model is simplified to consist of six Gauss vortices, representing four circumpolar cyclones (CPCs in yellow) and two anticyclonic white ovals (AWOs in blue). After a short simulation run, the vortices develop filamentary vorticity structures that are also apparent in the original JunoCam image, see detail in Fig. 2. Conjectures The above example suggests that the brightness of the cloud tops is correlated with the total amount of the relative vorticity. Intact vortices of similar size that touch each other are of opposite sign. They form a filamentary structure between them consisting of two parallel filaments of opposite vorticity. Two nearby cyclones are separated by a filament of anticyclonic vorticity. References [1] C.J. Hansen, M.A. Caplinger, A. Ingersoll, M.A. Ravine, E. Jensen, S. Bolton, G. Orton. Junocam: Juno’s Outreach Camera. Space Sci Rev 2013:475-506, 2017 [2] G. Eichstädt, C. Hansen, G. Orton. Fluid Dynamical 2D Simulations of Jupiter's South Polar Region Based On JunoCam Image Data. EGU2020-12025, https://doi.org/10.5194/egusphere-egu2020-12025

In the first 20 orbits of the Juno mission, over 150 waves and wave-like features have been detected by the JunoCam public-outreach camera. A wide variety of wave morphologies were detected over a wide latitude range, but the great majority were found near Jupiter’s equator. By analogy with previous studies of waves in Jupiter’s atmosphere, most of the waves detected are likely to be inertia-gravity waves. Introduction The Juno mission’s JunoCam instrument [1], has detected very small-scale waves. Our survey of JunoCam images revealed a surprising variety of features with wave-like morphologies. They are presented in terms of differences in visual morphology, without implication that this differentiation arises from the associated responsible dynamics. Types of waves Long wave packets with short, dark wave fronts represent 79% of the types of waves in our inventory, especially in the Equatorial Zone (EZ) that were also detected in previous studies. These include wave trains with orthogonal wave crests. Even more commonly, we detected wave packets with tilted fronts that are not oriented orthogonally to the wave packet direction. Both the meridional extent and wavelength of these waves are much shorter than the Rossby deformation radius, so it is logical to assume that they are formed by and interact with small-scale turbulence, and thereby propagate the waves in all directions (Fig. 1). Sometimes the short wavefronts are aligned in curved wave packets, all associated with larger features, and located outside the EZ. Short wave packets with wide wave fronts were also detected. In the Earth’s atmosphere, such waves are often associated with thunderstorms producing a brief impulse period with radiating waves. Wave packets with bright features appear bright on a dark background rather than dark on a lighter background, like the waves described above. Differences between darker and brighter wave crests could be the composition of the material affected. Lee waves, stationary waves generated by the vertical deflection of winds over an obstacle, were also detected. Jupiter’s atmosphere no doubt possesses the dynamical equivalent of an obstacle (Fig. 2). Waves associated with large vortices include compact cyclonic and anticyclonic features with extended radial wavefronts, resembling structures in terrestrial cyclonic hurricanes (Fig. 3). Long, parallel dark streaks are seen both with a non-uniform patterns and in regularly spaced parallel bands. Their orientation suggests that they are tracing out the direction of flow on streamlines. Physical properties Figure 4 plots the distribution of mean wavelengths for different types of waves and wave-like features as a function of latitude, co-plotted with mean zonal wind velocity. The minimum distance between crests is 29.1 km. The variability of wavelengths within a single packet is typically no greater than 20-30%. The equatorial waves with long packets and short crests in the EZ have wavelengths that are clustered between 30 km and 320 km, with most between 80 and 230 km in size. No waves are found at latitudes associated with retrograde zonal flow unless associated with a larger atmospheric feature. Conclusions JunoCam, detected 157 waves or wave-like features in its first 20 perijove passes. Of these, 100 are waves with long, linear packets and short crests. Another 25were detected with short packets and long crests. They are all likely to be truly propagating waves, which form the vast majority of features detected, concentrated in a latitude range between 5ºS and 7ºN. Few of these appear to be associated with other features except for waves that appear to be oriented in lines of local flow. There were fewer waves in the EZ between the equator and 1ºN than there were immediately north and south of this band, which was different from the waves detected by Voyager imaging in 1979 that were more equally distributed. Other waves outside the EZ are influenced by other features. These include waves associated with an anticyclonic or cyclonic eddies, lee waves some 10 km above the surrounding cloud deck. Several features appeared within or emanating from vortices. Two sets of extremely long, curved features were detected near the edges of a southwestern extension of a region associated with high 5-µm radiances at the southern edge of the NEB. No waves were detected south of 7ºS that were not associated with larger vortices, such as the GRS. No waves or wave-like features were detected in regions of retrograde mean zonal flow that were not associated with larger features, similar to the waves detected by Voyager imaging. Acknowledgements The primary support for this research was provided by NASA, a portion of which was distributed to the Jet Propulsion Laboratory, California Institute of Technology. References [1] Hansen et al. Junocam: Juno’s outreach camera. Space Sci. Rev. 217, 475-506. 2017. [2] Wong et al. High-resolution UV/optical/IR imaging of Jupiter in 2016–2019. Space Sci. Rev. 247, 58. 2020.

The Juno spacecraft provides unique close‐up views of Jupiter underneath the synchrotron radiation belts while circling Jupiter in its 53‐day orbits. The microwave radiometer (MWR) onboard measures Jupiter thermal radiation at wavelengths between 1.37 and 50 cm, penetrating the atmosphere to a pressure of a few hundred bars and greater. The mission provides the first measurements of Jupiter's deep atmosphere, down to ~250 bars in pressure, constraining the vertical distributions of its kinetic temperature and constituents. As a result, vertical structure models of Jupiter's atmosphere may now be tested by comparison with MWR data. Taking into account the MWR beam patterns and observation geometries, we test several published Jupiter atmospheric models against MWR data. Our residual analysis confirms Li et al.'s (2017, https://doi.org/10.1002/2017GL073159) result that ammonia depletion persists down to 50–60 bars where ground‐based Very Large Array was not able to observe. We also present an extension of the study that iteratively improves the input model and generates Jupiter brightness temperature maps which best match the MWR data. A feature of Juno's north‐to‐south scanning approach is that latitudinal structure is more easily obtained than longitudinal, and the creation of optimum two‐dimensional maps is addressed in this approach.

International audience; Observations of Jupiter's deep atmosphere by the Juno spacecraft have revealed several puzzling facts: The concentration of ammonia is variable down to pressures of tens of bars, and is strongly dependent on latitude. While most latitudes exhibit a low abundance, the Equatorial Zone of Jupiter has an abundance of ammonia that is high and nearly uniform with depth. In parallel, the Equatorial Zone is peculiar for its absence of lightning, which is otherwise prevalent most everywhere else on the planet. We show that a model accounting for the presence of small-scale convection and water storms originating in Jupiter’s deep atmosphere accounts for the observations. Where strong thunderstorms are observed on the planet, we estimate that the formation of ammonia-rich hail ('mushballs') and subsequent downdrafts can deplete efficiency the upper atmosphere of its ammonia and transport it efficiently to the deeper levels. In the Equatorial Zone, the absence of thunderstorms shows that this process is not occurring, implying that small-scale convection can maintain a near-homogeneity of this region. A simple model satisfying mass and energy balance accounts for the main features of Juno's MWR observations and successfully reproduces the inverse correlation seen between ammonia abundance and the lightning rate as function of latitude. We predict that in regions where ammonia is depleted, water should also be depleted to great depths. The fact that condensates are not well mixed by convection until far deeper than their condensation level has consequences for our understanding of Jupiter’s deep interior and of giant-planet atmospheres in general.

In the first 20 orbits of the Juno spacecraft around Jupiter, we have identified a variety of wave‐like features in images made by its public‐outreach camera, JunoCam. Because of Juno's unprecedented and repeated proximity to Jupiter's cloud tops during its close approaches, JunoCam has detected more wave structures than any previous surveys. Most of the waves appear in long wave packets, oriented east‐west and populated by narrow wave crests. Spacing between crests were measured as small as ~30 km, shorter than any previously measured. Some waves are associated with atmospheric features, but others are not ostensibly associated with any visible cloud phenomena and thus may be generated by dynamical forcing below the visible cloud tops. Some waves also appear to be converging, and others appear to be overlapping, possibly at different atmospheric levels. Another type of wave has a series of fronts that appear to be radiating outward from the center of a cyclone. Most of these waves appear within 5° of latitude from the equator, but we have detected waves covering planetocentric latitudes between 20°S and 45°N. The great majority of the waves appear in regions associated with prograde motions of the mean zonal flow. Juno was unable to measure the velocity of wave features to diagnose the wave types due to its close and rapid flybys. However, both by our own upper limits on wave motions and by analogy with previous measurements, we expect that the waves JunoCam detected near the equator are inertia‐gravity waves.

In the first 20 orbits of the Juno spacecraft around Jupiter, we have identified a variety of wave‐like features in images made by its public‐outreach camera, JunoCam. Because of Juno's unprecedented and repeated proximity to Jupiter's cloud tops during its close approaches, JunoCam has detected more wave structures than any previous surveys. Most of the waves appear in long wave packets, oriented east‐west and populated by narrow wave crests. Spacing between crests were measured as small as ~30 km, shorter than any previously measured. Some waves are associated with atmospheric features, but others are not ostensibly associated with any visible cloud phenomena and thus may be generated by dynamical forcing below the visible cloud tops. Some waves also appear to be converging, and others appear to be overlapping, possibly at different atmospheric levels. Another type of wave has a series of fronts that appear to be radiating outward from the center of a cyclone. Most of these waves appear within 5° of latitude from the equator, but we have detected waves covering planetocentric latitudes between 20°S and 45°N. The great majority of the waves appear in regions associated with prograde motions of the mean zonal flow. Juno was unable to measure the velocity of wave features to diagnose the wave types due to its close and rapid flybys. However, both by our own upper limits on wave motions and by analogy with previous measurements, we expect that the waves JunoCam detected near the equator are inertia‐gravity waves., Key Points In the first 20 orbits of the Juno mission, over 150 waves and wave‐like features have been detected by the JunoCam public‐outreach cameraA wide variety of wave morphologies were detected over a wide latitude range, but the great majority were found near Jupiter's equatorBy analogy with previous studies of waves in Jupiter's atmosphere, most of the waves detected are likely to be inertia‐gravity waves

Oxygen is the most common element after hydrogen and helium in Jupiter's atmosphere, and may have been the primary condensable (as water ice) in the protoplanetary disk. Prior to the Juno mission, in situ measurements of Jupiter's water abundance were obtained from the Galileo Probe, which dropped into a meteorologically anomalous site. The findings of the Galileo Probe were inconclusive because the concentration of water was still increasing when the probe died. Here, we initially report on the water abundance in the equatorial region, from 0 to 4 degrees north latitude, based on 1.25 to 22 GHz data from Juno Microwave radiometer probing approximately 0.7 to 30 bars pressure. Because Juno discovered the deep atmosphere to be surprisingly variable as a function of latitude, it remains to confirm whether the equatorial abundance represents Jupiter's global water abundance. The water abundance at the equatorial region is inferred to be $2.5_{-1.6}^{+2.2}\times10^3$ ppm, or $2.7_{-1.7}^{+2.4}$ times the protosolar oxygen elemental ratio to H (1$\sigma$ uncertainties). If reflective of the global water abundance, the result suggests that the planetesimals formed Jupiter are unlikely to be water-rich clathrate hydrates., Comment: 27 pages, 7 figures

A 1-dimensional microphysics model has been used to constrain the structure and formation of haze in Neptune's atmosphere. These simulations were coupled to a radiative-transfer and retrieval code (NEMESIS) to model spectral observations of Neptune in the H-band performed by the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope (VLT) in 2013. It was found that observations in the H-band and with emission angles ≤60° are largely unaffected by the imaginary refractive index of haze particles, allowing a notable reduction of the free parameters required to fit the observations. Our analysis shows a total haze production rate of (2.61 ± 0.18) × 10−14 kg m−2 s−1, about 10 times larger than that found in Uranus's atmosphere, and a particle electric charge of q = 8.6 ± 1.1 electrons per μm radius at latitudes between 5 and 15° S. This haze production rate in Neptune results in haze optical depths about 10 times greater than those in Uranus. The effective radius reff was found to be 0.22 ± 0.01 and 0.26 ± 0.02 μm at the 0.1 and 1-bar levels, respectively, with haze number densities of 8.48+1.78−1.31 and 9.31+2.52−1.91 particles per cm3. The fit at weak methane-absorbing wavelengths reveals also the presence of a tropospheric cloud with a total optical depth >10 at 1.46 μm. The tropospheric cloud base altitude was found near the 2.5-bar level, although this estimation may be only representative of the top of a thicker and deeper cloud. Our analysis leads to haze opacities about 3.5 times larger than that derived from Voyager-2 observations ( Moses et al., 1995 ). This larger opacity indicates a haze production rate 2 times larger at least. To study this difference haze opacity or production rate, we performed a timescale analysis with our microphysical model to estimate the time required for haze particles to grow and settle out. Although this analysis shows haze timescales (~15 years) shorter than the time lapsed between Voyager-2 observations and 2013, the solar illumination at the top of the atmosphere has not varied significantly during this period (at the studied latitudes) to explain the increase in haze production. This difference in haze production rate derived for these two periods may arise from: a) the fact that in our analysis we employed spectral observations in the infrared (H-band), while Moses et al. (1995) used photometric images taken at 5 different filters in the visible. While high-phase-angle Voyager observations are more sensitive to small haze particles and at altitudes above the 0.1-bar level, the haze constraints derived from VLT spectra in H-band are limited to pressures greater than 0.1 bar. As a result of the different phase angles of the two set of observations, differences in the estimation of M0 may arise from the use of Mie phase functions as well. b) our 1-dimensional model does not account for latitudinal redistributions of the haze by dynamics. A possible meridional transport of haze with wind velocities greater than ~0.03 m s−1 would result in dynamics timescales shorter than 15 years and thus might explain the observed variations in the haze production rate during this period. Compared with our estimations, photochemical models point to even larger production rates on Neptune (by a factor of 2.4). Assuming that the photochemical simulations are correct, we found that this discrepancy can be explained if haze particles evaporate before reaching the tropospheric-cloud levels. This scenario would decrease the cumulative haze opacity above the 1-bar level, and thus a larger haze production rate would be required to fit our observations. However, to validate this haze vertical structure future microphysical simulations that include the evaporation rates of haze particles are required.

We present multi-wavelength measurements of the thermal, chemical, and cloud contrasts associated with the visibly dark formations (also known as 5-$��$m hot spots) and intervening bright plumes on the boundary between Jupiter's Equatorial Zone (EZ) and North Equatorial Belt (NEB). Observations made by the TEXES 5-20 $��$m spectrometer at the Gemini North Telescope in March 2017 reveal the upper-tropospheric properties of 12 hot spots, which are directly compared to measurements by Juno using the Microwave Radiometer (MWR), JIRAM at 5 $��$m, and JunoCam visible images. MWR and thermal-infrared spectroscopic results are consistent near 0.7 bar. Mid-infrared-derived aerosol opacity is consistent with that inferred from visible-albedo and 5-$��$m opacity maps. Aerosol contrasts, the defining characteristics of the cloudy plumes and aerosol-depleted hot spots, are not a good proxy for microwave brightness. The hot spots are neither uniformly warmer nor ammonia-depleted compared to their surroundings at $p10$ bars, suggesting that the hot-spot/plume wave is a relatively shallow feature., 50 pages, 16 figures, accepted for publication in JGR-Planets

Within the first 26 orbits of the Juno spacecraft around Jupiter, we have identified a variety of wave-like features in images made by its public-outreach camera, JunoCam. Because of Juno’s unprecedented and repeated proximity to Jupiter’s cloud tops during its close approaches, JunoCam has detected more wave structures than any previous surveys. Most of the waves appear in long wave packets, oriented east-west and populated by narrow wave crests. Spacing between crests were measured as small as ~30 km, shorter than any previously measured. Some waves are associated with atmospheric features, but others are not ostensibly associated with any visible cloud phenomena and thus may be generated by dynamical forcing below the visible cloud tops. Some waves also appear to be converging and others appear to be overlapping, possibly at different atmospheric levels. Another type of wave has a series of fronts that appear to be radiating outward from the center of a cyclone. Although we have detected wave-like phenomena covering latitudes between 20°S and 45°N, most appear within 5° of latitude from the equator. Most waves appear in regions associated with prograde motions of the mean zonal winds. Although Juno was unable to measure the velocity of wave features to diagnose the wave types due to its close and rapid flybys, both by our own upper limits on wave motions and by analogy with previous measurements, we expect that the waves JunoCam detected near the equator are inertia-gravity waves.

During almost every perijove pass in more than three years of Juno's ~53-day polar orbits around Jupiter, its wide-angle visible-light camera, JunoCam [1], has imaged Jupiter's south polar region [2].We sought to determine whether these images could be used for prognostic “weather forecasts” in Jupiter. One of the simplest fluid dynamical models suitable for forecasting dynamical behavior of essentially barotropic incompressible flows of very low viscosity is the 2D Euler fluid. Vortex methods [3] are particularly suitable for modeling the resulting turbulence.Sequences of images taken with a cadence of several minutes reveal small motions of the cloud tops within the illuminated area of the pole. The south pole itself has been visible in the twilight.Raw JunoCam image data are transformed into an equidistant south-polar azimuthal map, roughly illumination-adjusted, high-passed with local contrast-normalization, and registered.A streamfunction describing the velocity field approximately is derived from a sequence of consecutive maps of a common perijove flyby. Running a Monte-Carlo approach for stereo correlation repeatedly with different pseudo-random number sets returns an ensemble of streamfunctions.The Laplacian of a streamfunction returns the vorticity values for a randomized 2D vortex particle seed as initial conditions of a grid-free vortex method. Applying the Biot-Savart law [3, p.19ff] on a 2-spherical geometry to the vorticity field returns the velocity field. A single-step explicit Runge-Kutta method of order 4 or 5 and fixed time steps advects the 4th-degree Gaussmollified vortex particles. Measuring the area of their Voronoi cells (Dirichlet/Thiessen polygons) reassesses the radius of the vortex particles. The method allows for some divergence. An approximately inviscid and incompressible 2D-flow is simulated over 2 up to 54 real-time days or about one Juno orbital period. The randomized nature of the method induces simulation ensembles for a given streamfunction by repeated runs.Reducing the streamfunction to a Morse-Smale complex returns idealized model vortex seeds.JunoCam images of the south polar region taken during a perijove pass provide an ensemble of dynamical data. These initial conditions extend to ensembles of forecast runs of the 2-spherical dynamics of the visible cloud tops in Jupiter's south polar region. We find that JunoCam images ofJupiter's south polar region allow for reasonably plausible forecasts of the dynamics of the observed area with grid-free 2D vortex methods over at least a few days.[1] C.J. Hansen, M.A. Caplinger, A. Ingersoll, M.A. Ravine, E. Jensen, S. Bolton, G. Orton.Junocam: Juno’s Outreach Camera. Space Sci Rev 2013:475-506, 2017[2] F.Tabataba-Vakili,J.H.Rogers,G.Eichstädt,G.S.Orton,C.J.Hansen,et al. Long-term Tracking ofCircumpolar Cyclones on Jupiter From Polar Observations with JunoCam. Icarus 335, 113405,2020.[3] G.-H. Cottet, P. D. Koumoutsakos, Vortex Methods: Theory and Practice, Cambridge UniversityPress, 2000

Atmospheric circulation patterns derived from multi-spectral remote sensing can serve as a guide for choosing a suitable entry site for a future in situ probe mission. Since the Voyager-2 flybys in the 1980s, three decades of observations from ground- and space-based observatories have generated a picture of Ice Giant circulation that is complex, perplexing, and altogether unlike that seen on the Gas Giants. This review seeks to reconcile the various competing circulation patterns from an observational perspective, accounting for spatially-resolved measurements of: zonal albedo contrasts and banded appearances; cloud-tracked zonal winds; temperature and para-H$_2$ measurements above the condensate clouds; and equator-to-pole contrasts in condensable volatiles (methane and hydrogen sulphide) in the deeper troposphere. These observations identify three distinct latitude domains: an equatorial domain of deep upwelling and upper-tropospheric subsidence, potentially bounded by peaks in the retrograde zonal jet and analogous to Jovian cyclonic belts; a mid-latitude transitional domain of upper-tropospheric upwelling, vigorous cloud activity, analogous to Jovian anticyclonic zones; and a polar domain of strong subsidence, volatile depletion, and small-scale (and potentially seasonally-variable) convective activity. Taken together, the multi-wavelength observations suggest a tiered structure of stacked circulation cells (at least two in the troposphere and one in the stratosphere), potentially separated in the vertical by (i) strong molecular weight gradients associated with cloud condensation, and by (ii) transitions from a thermally-direct circulation regime at depth to a wave-driven circulation regime at high altitude. The inferred circulation can be tested in the coming decade by 3D simulations and by observations from future world-class facilities. [Abridged], Comment: 29 pages, 8 figures, review article accepted to SSRv special issue on "In Situ Exploration of the Ice Giants"

We present results from mid-infrared imaging of Uranus at wavelengths of 13.0 micron and 18.7 micron, sensing emission from the stratosphere and upper troposphere, acquired using the VISIR instrument at the Very Large Telescope (VLT), September 4-October 20, 2018. Using a combination of inverse and forward modeling, we analyze these northern mid-spring (L_s~46) images and compare them to archival data to assess seasonal changes since the 1986 southern solstice and subsequent equinox. We find the data are consistent with little change (< 0.3 K) in the upper tropospheric temperature structure, extending the previous conclusions of Orton et al (2015) well past equinox, with only a subtle increase in temperature at the emerging north pole. Additionally, spatial-temporal variations in 13 micron stratospheric emission are investigated for the first time, revealing meridional variation and a hemispheric asymmetry not predicted by models. Finally, we investigate the nature of the stratospheric emission and demonstrate that the observed distribution appears related and potentially coupled to the underlying tropospheric emission six scale heights below. The observations are consistent with either mid-latitude heating or an enhanced abundance of acetylene. Considering potential mechanisms and additional observations, we favor a model of acetylene enrichment at mid-latitudes resulting from an extension of the upper-tropospheric circulation, which appears capable of transporting methane from the troposphere, through the cold trap, and into the stratosphere for subsequent photolysis to acetylene., 22 pages, 17 figures; Accepted for publication in The Astronomical Journal

Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53 days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14 filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm. We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near 35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data. Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the 15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The HST data maps multiple concentric polar hoods of high-latitude hazes.

The spatial distribution of water, ammonia, phosphine, germane, and arsine in the Jupiter's troposphere has been inferred from the Jovian Infrared Auroral Mapper (JIRAM) Juno data. Measurements allow us to retrieve the vertically averaged concentration of gases between ~3 and 5 bars from infrared‐bright spectra. Results were used to create latitudinal profiles. The water vapor relative humidity varies with latitude from

We present a power spectral analysis of two narrow annular regions near Jupiter's South Pole derived from data acquired by the Jovian Infrared Auroral Mapper instrument onboard NASA's Juno mission. In particular, our analysis focuses on the data set acquired by the Jovian Infrared Auroral Mapper M-band imager (hereafter IMG-M) that probes Jupiter's thermal emission in a spectral window centered at 4.8 μm. We analyze the power spectral densities of circular paths outside and inside of cyclones on images acquired during six Juno perijoves. The typical spatial resolution is around 55 km pixel-1. We limited our analysis to six acquisitions of the South Pole from February 2017 to May 2018. The power spectral densities both outside and inside the circumpolar ring seem to follow two different power laws. The wave numbers follow average power laws of -0.9 ± 0.2 (inside) and -1.2 ± 0.2 (outside) and of -3.2 ± 0.3 (inside) and -3.4 ± 0.2 (outside), respectively, beneath and above the transition in slope located at ~2 × 10-3 km-1 wave number. This kind of spectral behavior is typical of two-dimensional turbulence. We interpret the 500 km length scale, corresponding to the transition in slope, as the Rossby deformation radius. It is compatible with the dimensions of a subset of eddy features visible in the regions analyzed, suggesting that a baroclinic instability may exist. If so, it means that the quasi-geostrophic approximation is valid in this context.

This white paper, written in support of NASA's 2023-2032 Planetary Decadal Survey, outlines 10 major questions that focus on the origin, evolution, and current processes that shape the atmospheres of Uranus and Neptune. Prioritizing these questions over the next decade will greatly improve our understanding of this unique class of planets, which have remained largely unexplored since the Voyager flybys. Studying the atmospheres of the Ice Giants will greatly inform our understanding of the origin and evolution of the solar system as a whole, in addition to the growing number of exoplanetary systems that contain Neptune-mass planets., Comment: 8 pages, 0 figures, White Paper submitted to the Astrobiology and Planetary Science Decadal Survey

This whitepaper identifies important science questions that can be answered through exploration of the Jupiter System, with emphasis on the questions that can be addressed by the Europa Clipper Mission. We advocate for adding Jupiter System Science to the mission after launch when expanding the scientific scope will not affect the development cost., Comment: White Paper submitted to the Astrobiology and Planetary Science Decadal Survey

A time-variable 1D photochemical model is used to study the distribution of stratospheric hydrocarbons as a function of altitude, latitude, and season on Uranus and Neptune. The results for Neptune indicate that in the absence of stratospheric circulation or other meridional transport processes, the hydrocarbon abundances exhibit strong seasonal and meridional variations in the upper stratosphere, but that these variations become increasingly damped with depth due to increasing dynamical and chemical time scales. At high altitudes, hydrocarbon mixing ratios are typically largest where the solar insolation is the greatest, leading to strong hemispheric dichotomies between the summer-to-fall hemisphere and winter-to-spring hemisphere. At mbar pressures and deeper, slower chemistry and diffusion lead to latitude variations that become more symmetric about the equator. On Uranus, the stagnant, poorly mixed stratosphere confines methane and its photochemical products to higher pressures, where chemistry and diffusion time scales remain large. Seasonal variations in hydrocarbons are therefore predicted to be more muted on Uranus, despite the planet’s very large obliquity. Radiative-transfer simulations demonstrate that latitude variations in hydrocarbons on both planets are potentially observable with future JWST mid-infrared spectral imaging. Our seasonal model predictions for Neptune compare well with retrieved C(2)H(2) and C(2)H(6) abundances from spatially resolved ground-based observations (no such observations currently exist for Uranus), suggesting that stratospheric circulation — which was not included in these models — may have little influence on the large-scale meridional hydrocarbon distributions on Neptune, unlike the situation on Jupiter and Saturn.

The abundance of deuterium in giant planet atmospheres provides constraints on the reservoirs of ices incorporated into these worlds during their formation and evolution. Motivated by discrepancies in the measured deuterium-hydrogen ratio (D/H) on Jupiter and Saturn, we present a new measurement of the D/H ratio in methane for Saturn from ground-based measurements. We analysed a spectral cube (covering 1151-1160 cm$^{-1}$ from 6 February 2013) from the Texas Echelon Cross Echelle Spectrograph (TEXES) on NASA's Infrared Telescope Facility (IRTF) where emission lines from both methane and deuterated methane are well resolved. Our estimate of the D/H ratio in stratospheric methane, $1.65_{-0.21}^{+0.27} \times 10^{-5}$ is in agreement with results derived from Cassini CIRS and ISO/SWS observations, confirming the unexpectedly low CH$_{3}$D abundance. Assuming a fractionation factor of $1.34 \pm 0.19$ we derive a hydrogen D/H of $1.23_{-0.23}^{+0.27} \times 10^{-5}$. This value remains lower than previous tropospheric hydrogen D/H measurements of (i) Saturn $2.10 (\pm 0.13) \times 10^{-5}$, (ii) Jupiter $2.6 (\pm 0.7) \times 10^{-5}$ and (iii) the proto-solar hydrogen D/H of $2.1 (\pm 0.5) \times 10^{-5}$, suggesting that the fractionation factor may not be appropriate for stratospheric methane, or that the D/H ratio in Saturn's stratosphere is not representative of the bulk of the planet., 9 pages, 6 figures, 1 table

We present five epochs of WFC3 HST Jupiter observations taken between 2009–2016 and extract global zonal wind profiles for each epoch. Jupiter’s zonal wind field is globally stable throughout these years, but significant variations in certain latitude regions persist. We find that the largest uncertainties in the wind field are due to vortices or hot-spots, and show residual maps which identify the strongest vortex flows. The strongest year-to-year variation in the zonal wind profiles is the 24°N jet peak. Numerous plume outbreaks have been observed in the Northern Temperate Belt and are associated with decreases in the zonal velocity and brightness. We show that the 24°N jet peak velocity and brightness decreased in 2012 and again in late 2016, following outbreaks during these years. Our February 2016 zonal wind profile was the last highly spatially resolved measurement prior to Juno's first science observations. The final 2016 data were taken in conjunction with Juno’s perijove 3 pass on 11 December 2016, and show the zonal wind profile following the plume outbreak at 24°N in October 2016.

Juno is a PI-led mission to Jupiter, the second mission in NASA’s New Frontiers Program. The 3625-kg spacecraft spins at 2 rpm and is powered by three 9-meter-long solar arrays that provide ∼500 watts in orbit about Jupiter. Juno carries eight science instruments that perform nine science investigations (radio science utilizes the communications antenna). Juno’s science objectives target Jupiter’s origin, interior, and atmosphere, and include an investigation of Jupiter’s polar magnetosphere and luminous aurora.

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought.

The latitude-altitude map of ammonia mixing ratio shows an ammonia-rich zone at 0–5°N, with mixing ratios of 320–340 ppm, extending from 40–60 bars up to the ammonia cloud base at 0.7 bars. Ammonia-poor air occupies a belt from 5–20°N. We argue that downdrafts as well as updrafts are needed in the 0–5°N zone to balance the upward ammonia flux. Outside the 0–20°N region, the belt-zone signature is weaker. At latitudes out to ±40°, there is an ammonia-rich layer from cloud base down to 2 bars which we argue is caused by falling precipitation. Below, there is an ammonia-poor layer with a minimum at 6 bars. Unanswered questions include how the ammonia-poor layer is maintained, why the belt-zone structure is barely evident in the ammonia distribution outside 0–20°N, and how the internal heat is transported through the ammonia-poor layer to the ammonia cloud base.

The dark colors of Jupiter's North Equatorial Belt (NEB, $7-17^\circ$N) appeared to expand northward into the neighboring zone in 2015, consistent with a 3-5 year cycle of activity in the NEB. Inversions of thermal-IR imaging from the Very Large Telescope revealed a moderate warming and reduction of aerosol opacity at the cloud tops at $17-20^\circ$N, suggesting subsidence and drying in the expanded sector. Two new thermal waves were identified during this period: (i) an upper tropospheric thermal wave (wavenumber 16-17, amplitude 2.5 K at 170 mbar) in the mid-NEB that was anti-correlated with haze reflectivity; and (ii) a stratospheric wave (wavenumber 13-14, amplitude 7.3 K at 5 mbar) at $20-30^\circ$N. Both were quasi-stationary, confined to regions of eastward zonal flow, and are morphologically similar to waves observed during previous expansion events.

We present retrievals of the vertical temperature profile of Jupiter's high-latitudes from IRTF-TEXES measurements acquired on December 10-11th 2014 and April 30th-May 1st 2016. Over this time range, 1-mbar temperatures in Jupiter's northern and southern auroral regions exhibited independent evolution. The northern auroral hotspot exhibited negligible net change in temperature at 1 mbar and its longitudinal position remained fixed at 180° W (System III) whereas, the southern auroral hotspot exhibited a net increase in temperature of 11.1 ± 5.2 K at 0.98 mbar and its longitudinal orientation moved west by approximately 30° . This southern auroral stratospheric temperature increase might be related to: 1) near-contemporaneous brightening of the southern auroral ultraviolet/near-infrared H3+ emission measured by the Juno spacecraft and 2) an increase in the solar dynamical pressure in the preceding 3 days. We therefore suggest 1-mbar temperatures in the southern auroral region might be modified by higher-energy charged particle precipitation.

The Juno microwave radiometer measured the thermal emission from Jupiter's atmosphere from the cloud tops at about 1 bar to as deep as a hundred bars of pressure during its first flyby over Jupiter (PJ1). The nadir brightness temperatures show that the Equatorial Zone is likely to be an ideal adiabat, which allows a determination of the deep ammonia abundance in the range 362^(+33)_(-33) ppm. The combination of Markov chain Monte Carlo method and Tikhonov regularization is studied to invert Jupiter's global ammonia distribution assuming a prescribed temperature profile. The result shows (1) that ammonia is depleted globally down to 50–60 bars except within a few degrees of the equator, (2) the North Equatorial Belt is more depleted in ammonia than elsewhere, and (3) the ammonia concentration shows a slight inversion starting from about 7 bars to 2 bars. These results are robust regardless of the choice of water abundance.

Juno swoops around giant Jupiter Jupiter is the largest and most massive planet in our solar system. NASA's Juno spacecraft arrived at Jupiter on 4 July 2016 and made its first close pass on 27 August 2016. Bolton et al. present results from Juno's flight just above the cloud tops, including images of weather in the polar regions and measurements of the magnetic and gravitational fields. Juno also used microwaves to peer below the visible surface, spotting gas welling up from the deep interior. Connerney et al. measured Jupiter's aurorae and plasma environment, both as Juno approached the planet and during its first close orbit. Science , this issue p. 821 , p. 826

During Juno's first perijove encounter, the JunoCam instrument acquired the first images of Jupiter's polar regions at 50–70 km spatial scale at low emission angles. Poleward of 64–68° planetocentric latitude, where Jupiter's east-west banded structure breaks down, several types of discrete features appear on a darker background. Cyclonic oval features are clustered near both poles. Other oval-shaped features are also present, ranging in size from 2000 km down to JunoCam's resolution limits. The largest and brightest features often have chaotic shapes. Two narrow linear features in the north, associated with an overlying haze feature, traverse tens of degrees of longitude. JunoCam also detected an optically thin cloud or haze layer past the northern nightside terminator estimated to be 58 ± 21 km (approximately three scale heights) above the main cloud deck. JunoCam will acquire polar images on every perijove, allowing us to track the state and evolution of longer-lived features.

During the first perijove passage of the Juno mission, the Jovian InfraRed Auroral Mapper (JIRAM) observed a line of closely spaced oval features in Jupiter's southern hemisphere, between 30°S and 45°S. In this work, we focused on the longitudinal region covering the three ovals having higher contrast at 5 μm, i.e., between 120°W and 60°W in System III coordinates. We used the JIRAM's full spectral capability in the range 2.4–3 μm together with a Bayesian data inversion approach to retrieve maps of column densities and altitudes for an NH3 cloud and an N2H4 haze. The deep (under the saturation level) volume mixing ratio and the relative humidity for gaseous ammonia were also retrieved. Our results suggest different vortex activity for the three ovals. Updraft and downdraft together with considerations about the ammonia condensation could explain our maps providing evidences of cyclonic and anticyclonic structures.

We describe a huge planetary-scale disturbance in the highest-speed Jovian jet at latitude 23.5°N that was first observed in October 2016 during the Juno perijove-2 approach. An extraordinary outburst of four plumes was involved in the disturbance development. They were located in the range of planetographic latitudes from 22.2° to 23.0°N and moved faster than the jet peak with eastward velocities in the range 155 to 175 m s−1. In the wake of the plumes, a turbulent pattern of bright and dark spots (wave number 20–25) formed and progressed during October and November on both sides of the jet, moving with speeds in the range 100–125 m s−1 and leading to a new reddish and homogeneous belt when activity ceased in late November. Nonlinear numerical models reproduce the disturbance cloud patterns as a result of the interaction between local sources (the plumes) and the zonal eastward jet.

The Juno Microwave Radiometer (MWR) is a six-frequency scientific instrument designed and built to investigate the deep atmosphere of Jupiter. It is one of a suite of instruments on NASA’s New Frontiers Mission Juno launched to Jupiter on August 5, 2011. The focus of this paper is the description of the scientific objectives of the MWR investigation along with the experimental design, observational approach, and calibration that will achieve these objectives, based on the Juno mission plan up to Jupiter orbit insertion on July 4, 2016. With frequencies distributed approximately by octave from 600 MHz to 22 GHz, the MWR will sample the atmospheric thermal radiation from depths extending from the ammonia cloud region at around 1 bar to pressure levels as deep as 1000 bars. The primary scientific objectives of the MWR investigation are to determine the presently unknown dynamical properties of Jupiter’s subcloud atmosphere and to determine the global abundance of oxygen and nitrogen, present in the atmosphere as water and ammonia deep below their respective cloud decks. The MWR experiment is designed to measure both the thermal radiation from Jupiter and its emission-angle dependence at each frequency relative to the atmospheric local normal with high accuracy. The antennas at the four highest frequencies (21.9, 10.0, 5.2, and 2.6 GHz) have ∼12° beamwidths and will achieve a spatial resolution approaching 600 km near perijove. The antennas at the lowest frequencies (0.6 and 1.25 GHz) are constrained by physical size limitations and have 20° beamwidths, enabling a spatial resolution of as high as 1000 km to be obtained. The MWR will obtain Jupiter’s brightness temperature and its emission-angle dependence at each point along the subspacecraft track, over angles up to 60° from the normal over most latitudes, during at least six perijove passes after orbit insertion. The emission-angle dependence will be obtained for all frequencies to an accuracy of better than one part in 10^3, sufficient to detect small variations in atmospheric temperature and absorber concentration profiles that distinguish dynamical and compositional properties of the deep Jovian atmosphere.

Microphysical simulations have been performed to constrain the formation and structure of haze in Uranus's atmosphere. These simulations were coupled to a radiative-transfer code to fit observations performed by the SINFONI Integral Field Unit Spectrometer on the Very Large Telescope (VLT)and by the Wide Field Camera 3 (WFC3)of the Hubble Space Telescope (HST)in 2014. Our simulations yield an effective radius of ∼0.2 μm for the haze particles in the tropopause and a density of ∼2.9 particles per cm 3. Our simulations also provide an estimate for the haze production rate in the stratosphere of between ∼3.10 −16 and 3.10 −15 kg m −2 s −1, about 100 times smaller than that found in Titan's atmosphere (e.g. Rannou et al., 2004). This range of values is very similar to that derived by Pollack et al. (1987)from Voyager-2 observations in 1986, suggesting microphysical timescales greater than the elapsed time between these observations (28 years, or 1/3 of a Uranian year). This result is in agreement with analyses performed with our microphysical model that show timescales for haze particles to grow and settle out to be >∼30 years at pressure levels >0.1 bar. However, these timescales are too big to explain the observed variations in the haze structure over Uranus's northern hemisphere after 2007 equinox (e.g. de Pater et al., 2015). This indicates that dynamics may be the main factor controlling the spatial and temporal distribution of the haze over the poles. A meridional stratospheric transport of haze particles with winds velocities >∼0.025 m s −1 would result in dynamics timescales shorter than 30 years and thus may explain the observed variations in the haze structure.

High spatial resolution images of Jupiter at 1.58–2.28 μm are used to track and characterize a wave pattern observed in 2017 at a planetocentric latitude of 14°N. The wave pattern has a wave number of 18 and spans ∼5° in latitude. One bright crest remains stationary in System III longitude, while the remaining crests move slowly westward. The bright and dark regions of the near‐infrared wave pattern are caused by variations in the vertical location of the upper tropospheric haze layer. A comparison with thermal infrared observations shows a correlation with temperature anomalies in the upper troposphere. The results are consistent with a Rossby wave, generated by flow around a stationary vortex.

International audience; Observations of Neptune, made in 2018 using the new Narrow Field Adaptive Optics mode of the Multi Unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT) from 0.48 to 0.93 μm, are analysed here to determine the latitudinal and vertical distribution of cloud opacity and methane abundance in Neptune's observable troposphere (0.1-∼ 3bar). Previous observations at these wavelengths in 2003 by HST/STIS (Karkoschka and Tomasko 2011, Icarus 205, 674-694) found that the mole fraction of methane above the cloud tops (at ∼ 2 bar) varied from ∼ 4% at equatorial latitudes to ∼ 2% at southern polar latitudes, by comparing the observed reflectivity at wavelengths near 825 nm controlled primarily by either methane absorption or H2-H2/H2-He collision-induced absorption. We find a similar variation in cloud-top methane abundance in 2018, which suggests that this depletion of methane towards Neptune's pole is potentially a long-lived feature, indicative of long-term upwelling at mid-equatorial latitudes and subsidence near the poles. By analysing these MUSE observations along the central meridian with a retrieval model, we demonstrate that a broad boundary between the nominal and depleted methane abundances occurs at between 20 and 40°S. We also find a small depletion of methane near the equator, perhaps indicating subsidence there, and a local enhancement near 60-70°S, which we suggest may be associated with South Polar Features (SPFs) seen in Neptune's atmosphere at these latitudes. Finally, by the use of both a reflectivity analysis and a principal component analysis, we demonstrate that this depletion of methane towards the pole is apparent at all locations on Neptune's disc, and not just along its central meridian.

We obtained the first maps of Jupiter at 1-3 mm wavelength with the Atacama Large Millimeter/Submillimeter Array (ALMA) on 3-5 January 2017, just days after an energetic eruption at 16.5S jovigraphic latitude had been reported by the amateur community, and about 2-3 months after the detection of similarly energetic eruptions in the northern hemisphere, at 22.2-23.0N. Our observations, probing below the ammonia cloud deck, show that the erupting plumes in the SEB bring up ammonia gas from the deep atmosphere. While models of plume eruptions that are triggered at the water condensation level explain data taken at uv-visible and mid-infrared wavelengths, our ALMA observations provide a crucial, hitherto missing, link in the moist convection theory by showing that ammonia gas from the deep atmosphere is indeed brought up in these plumes. Contemporaneous HST data show that the plumes reach altitudes as high as the tropopause. We suggest that the plumes at 22.2-23.0N also rise up well above the ammonia cloud deck, and that descending air may dry the neighboring belts even more than in quiescent times, which would explain our observations in the north., Comment: 28 pages, 12 figures, 4 tables

Recent analysis of Gemini-North/NIFS H-band (1.45 - 1.8 $\mu$m) observations of Uranus, recorded in 2010, with recently updated line data has revealed the spectral signature of hydrogen sulphide (H$_2$S) in Uranus's atmosphere (Irwin et al., 2018). Here, we extend this analysis to Gemini-North/NIFS observations of Neptune recorded in 2009 and find a similar detection of H$_2$S spectral absorption features in the 1.57 - 1.58 $\mu$m range, albeit slightly less evident, and retrieve a mole fraction of $\sim1-3$ ppm at the cloud tops. We find a much clearer detection (and much higher retrieved column abundance above the clouds) at southern polar latitudes compared with equatorial latitudes, which suggests a higher relative humidity of H$_2$S here. We find our retrieved H$_2$S abundances are most consistent with atmospheric models that have reduced methane abundance near Neptune's south pole, consistent with HST/STIS determinations (Karkoschka and Tomasko, 2011). We also conducted a Principal Component Analysis (PCA) of the Neptune and Uranus data and found that in the 1.57 - 1.60 $\mu$m range, some of the Empirical Orthogonal Functions (EOFs) mapped closely to physically significant quantities, with one being strongly correlated with the modelled H$_2$S signal and clearly mapping the spatial dependence of its spectral detectability. Just as for Uranus, the detection of H$_2$S at the cloud tops constrains the deep bulk sulphur/nitrogen abundance to exceed unity (i.e. $ > 4.4 - 5.0$ times the solar value) in Neptune's bulk atmosphere, provided that ammonia is not sequestered at great depths, and places a lower limit on its mole fraction below the observed cloud of (0.4 - 1.3) $\times 10^{-5}$. The detection of gaseous H$_2$S at these pressure levels adds to the weight of evidence that the principal constituent of the 2.5 - 3.5-bar cloud is likely to be H$_2$S ice., Comment: 13 Figures

Jupiter's banded structure undergoes strong temporal variations, changing the visible and infrared appearance of the belts and zones in a complex and turbulent way due to physical processes that are not yet understood. In this study we use ground-based 5-$\mu$m infrared data captured between 1984 and 2018 by 8 different instruments mounted on the Infrared Telescope Facility in Hawai'i and on the Very Large Telescope in Chile to analyze and characterize the long-term variability of Jupiter's cloud-forming region at the 1-4 bar pressure level. The data show a large temporal variability mainly at the equatorial and tropical latitudes, with a smaller temporal variability at mid-latitudes. We also compare the 5-$\mu$m-bright and -dark regions with the locations of the visible zones and belts and we find that these regions are not always co-located, specially in the southern hemisphere. We also present Lomb-Scargle and Wavelet Transform analyzes in order to look for possible periodicities of the brightness changes that could help us understand their origin and predict future events. We see that some of these variations occur periodically in time intervals of 4-8 years. The reasons of these time intervals are not understood and we explore potential connections to both convective processes in the deeper weather layer and dynamical processes in the upper troposphere and stratosphere. Finally we perform a Principal Component analysis to reveal a clear anticorrelation on the 5-$\mu$m brightness changes between the North Equatorial Belt and the South Equatorial Belt, suggesting a possible connection between the changes in these belts., Comment: Accepted in the Astronomical Journal