Gerald Eichstädt

During Juno’s approach to Perijove 58, her wide-angle visible light imager JunoCam took a sequence of Io images. Four of those images show the lava lake Loki Patera with a solar specular deviation angle varying approximately between 0.25 and 0.8 radians.We call the angle between the solar specular vector relative to Io’s nominal surface normal and the vector from the respective surface point to the camera the solar specular deviation angle. We call the angle between the plane defined by the sun and the respective surface normal solar specular azimuth when seen relative to the solar specular vector. This construct is similar to polar azimuthal coordinates, just with the solar specular vector as symmetry axis, and the vector to the Sun being used to define the zero azimuth.We sample an annulus around the lava lake in order to estimate relative exposure times and dark biases by applying linear least-square regression. This approach is described in Figure 1.Figure 1: Crops of cylindrical map projections of the four JunoCam images 26, 27, 28, and 29 taken before Perijove 58 are shown in the first row, together with a mask that defines an annular area around the lava lake of Loki Patera. North is to the right. Samples within this annulus are taken for images 27, 28, and 29, and brightness-correlated to the same locations in image 26. The second row shows the resulting correlation diagrams. Linear least-square regression is applied to those data sets as an approximation of a calibration of images 27, 28, and 29 relative to image 26. The resulting calibrated correlation is shown in the third row. The fourth row shows the residuals betweem consecutive images, hence for image pairs (26-27), (27-28), and (28-29).The residuals remove most of the area outside the lava lakes. The lava lakes themselves show up very distinctly. We use this property for image pair (26-27) together with the red/green slope of image 26, and with a draft elliptical area selection, as a heuristics to define a mask that covers the lava lake. This mask is then further eroded in order to make sure that sampling within the mask does contain only interior points of the lava lake area, see Figure 2.Figure 2: The first row visualizes steps from the difference (26-27) of calibrated images 26 and 27, over a mask that covers the lava lake area, to an eroded mask that covers only the interior area of Loki Patera. The second row plots the mask and the masked and calibrated caldera in coordinates of the solar specular deviation angle and azimuth, both in radians, and applied to all four considered images. Since the Juno spacecraft is changing her position with each image, the lava lake changes its apparent position relative to the solar specular vector. Compared to the surrounding area of the lava lake, its interor area is brightest for image 26, and dims until image 29, while the solar specular deviation angle is increasing. The y axis at the left border of the two panels at the bottom defines the solar specular vector, along which a perfect spherical mirror with Io’s radius and center would reflect the sunlight. With this prerequisites, we sample Loki Patera along contour lines of either constant solar specular deviation angle, or of constant solar specular azimuth. Sampling is restricted to the eroded mask in order to retrieve only valid samples from the interior of the lava lake area. Both cases are visualized in Figure 3.Figure 3: The first row samples along the contour line with a solar specular azimuth equal to 3.0 radians. The second row samples along the line with a specular deviation angle of 0.3 radians. The left column shows the sampling tracks in cylindrical map projections. The right column shows the brightness charts of the red channel. The effect of the solar specular deviation angle is significant and locally close to linear, while the effect of the azimuth can be interpreted as weakly linear, not quite constant, and noisy, or influenced by local heterogeneities.Samples taken along contour lines suggest that brightness values of the lava lake can be reasonably approximated patera-locally, and for each image separately by linear regression over two dimensions with the solar specular deviation angle and azimuth as axes.Concavity of the brightness plot becomes apparent only after combining charts of a sequence of images.

Jupiter’s north pole is attended by eight circumpolar cyclones (CPCs) surrounding a central North Polar Cyclone (NPC) [Fig.1]. They were discovered by the JunoCam and JIRAM instruments on Juno (Ref.1), and have been remarkably stable ever since. Here we use JunoCam maps to track the positions of the CPCs and NPC throughout the Juno mission, as well as the behaviour of several ancillary circulations which have persisted for some time. CPC-7 is always further from the pole than the others, and the NPC is always offset into one quadrant by up to 1.2° from the pole.Circumpolar cyclonesHere we track longitudes of the 8 CPCs up to perijove (“PJ”) 73 [Fig.2], extending the analysis of Ref.2. The CPCs have only shown modest changes on longitude. The results show that the octagon moves largely as a whole, with trends on a timescale of several months to a year. Most of the CPCs decreased slightly in longitude up to PJ8 then increased between PJ12 and PJ17, as already shown in Ref.2. The CPCs have been generally stationary since then, except between PJ31 and PJ42, when they all increased in longitude substantially then decreased again, though remaining several degrees higher than before. This positive excursion peaked between PJ35 and PJ38, not quite synchronously for all the CPCs, with an increase of 8°-18° relative to their overall mean motion; all other deviations from the mean motion were smaller. Since then, they have all been essentially stationary since then apart from CPC-7 and CPC-6. Overall, the CPCs longitudes have increased by an average of 16 (±5) deg in 9.0 years, but variations are neither progressive nor cyclic.These results show that the north polar octagon does not copy the systematic rotation and precessional motion of the south polar pentagon (Refs.2, 4, 5), which have been reproduced in a model by Gavriel & Kaspi (Ref.6). However, the lag between longitude changes of CPCs suggests that similar interactions between adjacent cyclones may occur. We also briefly detail the varying morphologies of each of the CPCs, noting that they tend to fall into either a ‘filled’ category or a more diverse category including spiral and chaotic forms. The ‘filled’ CPCs have mostly grown larger during Juno’s mission, especially CPC-1. Only CPC-5 has not grown. This may suggest a seasonal change, although any reversion to smaller size would have to occur rapidly during the so-far-unobserved portion of the jovian year. The NPC itself, while appearing as a spiral form, and consistently so, is quite different from the others in radio wavelengths (see other presentations this conference). Extra circulationsWhile the 8 CPCs and the NPC are the only features that have persisted throughout Juno’s mission, several other circulations in and around the octagon have been followed for multiple perijoves.Anticyclonic white ovals (AWOs) inside the octagon: There are always one or two AWOs inside the octagon. One is usually present poleward of CPC-7 (except PJ32 to PJ39) [Fig. 1: PJ57/58 map]; the other (b) was seen from PJ25 to PJ55, poleward of CPCs-3/4/5, though swinging unpredictably in longitude. It seems likely that the two merged just after PJ57, creating an AWO poleward of CPC-1 from PJ62 to PJ70, while a new vortex developed poleward of CPC-7.AWO just outside the octagon: A large AWO was tracked from PJ47 to PJ70. [Fig.3. PJ43-PJ70]. After eddying in a small clockwise loop from PJ43 to PJ47, from PJ47 to PJ51 it drifted anticlockwise around the periphery of the octagon at 79.5 (±0.14)°N, consistent with the outer winds of the CPCs. Then at PJ52 it had probably merged with a smaller AWO, and almost stopped moving. From PJ53 to PJ64 it remained just S of CPC-1&2, again oscillating slightly in clockwise loops. At PJ64 it apparently broke loose from this eddy and moved to a lower latitude, then from PJ67 to PJ70 it drifted clockwise (retrograde) around the octagon at 78.0—79.0°N. Ancillary cyclones: Sometimes one or two extra cyclones are seen at corners of the octagon, resembling smaller versions of filled CPCs, added to the vortex crystal. Two lasted for some time. One, labelled ‘X’, was recorded from PJ30 to PJ45 [Fig 5]. At PJ50, it was either absent or reduced, but a small cyclone from PJ58 to PJ66 may qualify as a revival of ‘X’. The other ancillary cyclone is labelled ‘IX’ [Fig 4. PJ32-PJ39]. At PJ32 & PJ33 it was a small version of a ‘filled’ CPC. At PJ36 to PJ39, if this was the same object, it had a similar cloud texture but an elongated, distorted outline, and it was drifting clockwise (retrograde) around the octagon at 77.6—78.7°N. These drifts, for the cyclone and the AWO, did not exceed 2.1 m/s, and were usually < 1 m/s -- much slower than the wind speeds in CPCs or jets. They are consistent with the flow patterns that we found around the south polar polygon: AWOs with variable prograding drift adjacent to the CPCs [Ref.2], and a zone slightly further out in which the average drift was weakly retrograding [Ref.3].Acknowledgements: We thank Michael Ravine and Michael Caplinger (Malin Space Science Systems) and Tom Momary (formerly JPL) for enabling the operation of JunoCam. Some of this research was funded by NASA, in part through JPL/CalTech. References:1. Adriani A et al. (2018), Nature 555, 216-219. 2. Tabataba-Vakili F et al.(2019/20), Icarus 335, paper 113405. https://doi.org/10.1016/j.icarus.2019.1134053. Rogers J et al. (2021/22), Icarus 372, paper 114742. https://doi.org/10.1016/j.icarus.2021.1147424. Rogers J et al. (2021), EPSC Abstracts Vol. 15, EPSC2021-57, 2021. https://doi.org/10.5194/epsc2021-575. Mura A et al. (2021), GRL 48, e2021GL094235. https://doi.org/10.1029/2021gl0942356. Gavriel N & Kaspi Y (2022), GRL 49, e2022GL098708. https://doi.org/10.1029/2022GL098708

JunoCam, the wide-angle visible light imager of NASA's Juno mission to Jupiter delivers excellent close-up images of Jupiter's cloud tops. Juno's mission on its elliptical, and precessing polar orbit was initially anticipated to end before crossing Europa's orbit. Any data taken from the Europa flyby onwards has come from a mission extension with opportunistic and serendipitous observations. Besides unprecedented close-up views of Jupiter's north polar region in the visible light spectrum, JunoCam was able to take close-up image sequences of Io, including specular reflection from the glassy surface of some of its calderas. A very subtle streak of light through Io observed after a violent eruption of one of its volcanoes suggests the demand for follow-up observations by other instruments such as JWST, in order to find out whether this is simply an instrument artefact, or whether we see Io inducing an arc of material escaping its Hill sphere with possible implications for a steady supply of material to Europa. While JunoCam was intended to take close-up images of Jupiter's dayside, it transitioned to taking close-up images of Jupiter's night side. Due to JunoCam's design using time-delayed integration, it can take sharp images despite the camera being statically attached to the rotating spacecraft. This technology, together with thorough image cleaning, was successfully applied to capture lightning and an auroral arc. Juno's precessing polar orbit brings the spacecraft closer to Jupiter's most intense radiation belt. Charged particles, mostly energetic electrons, cause visible energetic particle hits on the CCD, and they degrade the detector. While this creates challenges for processing pretty images, and even for instrument health, it can also be used to retrieve qualitative data on charged particle flux and total dose.

Outbreaks of activity on the eastward jet stream on the south edge of the North Temperate Belt (NTBs jet) are spectacular, infrequent phenomena, which include the brightest and fastest-moving spots that Jupiter ever displays. These are believed to be tall plumes driven by moist convection in the water cloud layer below the visible clouds, where the jet is faster than at the cloud tops (‘super-fast’) [refs.1&2]. Currently they occur every 4 to 5 years [ref.3]. The latest outbreak began on 2025 Jan.10, and has been one of the best observed ever. Here we describe the great plumes and smaller ‘wake-induced plumelets’ as recorded by amateur observers and by JunoCam. A companion abstract (ODAA4 session) describes the zonal wind profiles and feature drifts as they changed during the cycle.Because of the high speed of the NTBs jet, maps and charts are plotted in System 1 longitude (L1) unless otherwise stated. Drift rates (DL1) are given in degrees per day; DL3 = DL1 - 7.364 deg/day. Latitudes are planetographic.The three primary plumes: Plume 1 is shown in Figure 1. It was extremely bright at all wavelengths, especially the methane absorption band (889 nm). In Fig.1A, the brightest cloud in the methane band (the head of the plume) was not the brightest in RGB and near-IR continuum, showing that different parts were at different levels. The second primary plume (only 20º p. plume 1) appeared on Jan.27, and the third (dubbed Plume 5) on Feb.9. Early acceleration and latitude shift: All three plumes first appeared at 24.0-24.6ºN, then drifted south and accelerated within a few days (Fig.2), to remain at 23.3 (±0.3)ºN with sustained speeds of DL1 = -5.0, -5.1, and -4.6 deg/day (u = 160-167 m/s). The early acceleration could be due to the change in latitude, following a fixed zonal wind profile (see companion abstract). This behaviour supports the theoretical model [ref.2], in which the plumes were convective storms rising from the super-fast jet in the water-cloud layer, initiated with an arbitrary heat pulse; but modelling required this initial source to be at about 24.5ºN, not at the mature plume latitude. This is just what we have observed for all three plumes in 2025. However in 2020, while the three plumes showed a similar early acceleration, we did not find any significant shift in latitude, despite high-quality observations [ref.3].Plume 1 with lightning: It is well known that many convective eruptions on Jupiter are thunderstorms, but until now there was no direct proof for these greatest of all plumes. On Jan.28/29, Juno flew past Jupiter at perijove-69 (PJ69). The outbreak was not in JunoCam’s field of view during the sunlit inbound phase; but a dark-side image revealed two lightning flashes or clusters at 23.2ºN (20.6ºN planetocentric), near the edge of the frame. The brighter of these was on the edge of the head of plume 1 (Fig.4), confirming that the plume is a thunderstorm.Demise of the plumes: The plumes always disintegrate within a few days when they catch up with the slower-moving wake of the next plume to the east, and this happened to plume 1 on/about Feb.2 (Fig.3). Thereafter, plumes 2 and 5 persisted at full strength until Feb.25, when they each caught up with the expanding wake of the other and started to fade. By March 1 only small remnants were left. This suggests that the convection can no longer be sustained where these storms have disrupted the pre-existing vertical atmospheric layering. Both also decelerated after Feb.25, and moved slightly south, to ~22.7ºN. This may mean that the surface current was still less than the super-fast speed of the plumes, so as soon as their deep convection was cut off, they began to be advected with the higher-level winds, like small northerly bright spots trailing behind the plumes earlier. Juno's PJ70 occurred on March 2, and JunoCam would have had a fine view of plume 5, but it had just disappeared . So JunoCam obtained an excellent view of the turbulent wake just afterwards (Fig.5).Wake-induced plumelets: Bright spots were repeatedly observed near the following (west) end of the wake, which seemed to be weaker versions of the main plumes, therefore designated as plumes 3,4,6,7,8 (e.g. Fig.3). They were also methane-bright, and accelerated to speeds almost as fast as the main plumes, but only lasted for 3-10 days. Mean drifts were ~-3.9 to -4.6 deg/day (u ≈ 150-160 m/s), at 23.2 to 24.1ºN. We suggest that the intense disturbance along the wake of the outbreak, while suppressing the jet speed at cloud-top level, is sensed in the super-fast water layer just beyond the end of the wake and thus triggers short-lived plumes, but these are themselves disrupted as they advance into the wake. These wake-induced plumelets have also been observed in some previous outbreaks and are a newly-recognised feature of these events. Fig.6 is a sketch of our present model of the outbreak.In our companion abstract (ODAA4 session), we show that the cloud-top winds never achieved the full speed of the deeper super-fast jet as shown by the plumes and plumelets. Full details of these studies are in our 2024/25 Report no.5 [ref.4]. Details of the observations are posted in our regular reports on the JunoCam and BAA websites: https://www.missionjuno.swri.edu/junocam; https://britastro.org/sections/jupiter.Acknowledgements: Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA (80NM0018D0004).References:Sanchez-Lavega A et 24 al. (2008) Nature 451, 437-440. Depth of a strong jovian jet from a planetary-scale disturbance driven by storms. Sanchez-Lavega A, Rogers JH, et al.(2017). ‘A planetary-scale disturbance in the most intense Jovian atmospheric jet from JunoCam and ground-based observations.’ GRL 44, 4679–4686. DOI: 10.1002/2017GL073421 Rogers J & Adamoli G (2021): ‘Jupiter...

JunoCam images show a stable and approximately irrotational north polar cyclone, surrounded by eight circumpolar cyclones (CPCs) (Figure 1). The CPCs have been essentially stable over almost a decade since their discovery in 2016. They show only a minor zonal drift. Some of the CPCs develop and maintain a counter-rotating core that remains sustained over several months or longer. Those CPCs show a much stronger signature in MWR data than CPCs without a large embedded counter-rotating vortex. Between the north polar cyclone and the surrounding CPCs, up to about two additional large anti-cyclones occur that are not as stable or as long-lasting as the CPCs.Figure 1: North polar CPC cluster seen by MWR and JunoCam. The north polar cyclone is nearly invisible in MWR data. CPCs with counter-rotating core tend to be brighter in MWR.We have used a two-layer fluid dynamical model. In its first 2D layer we have assumed a steady flow with a north polar cyclone surrounded by CPCs with an optional counter-rotating core. A coupled second 2D layer behaves like an incompressible Euler flow, except for its coupling defined by a vorticity flux proportional to the vorticity difference between the two layers. This model develops almost no vertical vorticity flux for the north polar cyclone, but more vorticity flux for CPCs with a counter-rotating core than for those without such a feature, see Figure 2.Figure 2First row: Two-layer fluid model with an assumed steady 2D flow in layer 1 in the left panel, the simulated fluid layer 2 in the right panel, and the required vorticity flux at the center. Yellow means north anticylonic, blue means cyclonic vorticity.Second row: Simulated vorticity flux blurred with color scheme adjusted to that of MWR. The model vorticity flux resembles MWR data while the simulated fluid layer resembles JunoCam data. It is important to note that JunoCam is an optical imager and therefore sees the cloud tops, while MWR is a microwave radiometer whose 6 channels see thermal emission from about the 1-bar level to about the 100-bar level. Vertical vorticity flux between simulated layers might be interpreted as related to convection and induced heat transport between otherwise geostrophic fluid layers. This may then show up in temperature deviations in MWR data. Since the north polar cyclone and the CPCs without a counter-rotating core are closer to an equilibrium, and require less vorticity flux to remain stable, their geostrophic layer shows less temperature anomalies in MWR. However, this conceivable physical interpretation is beyond the limitations of the simplified empirical model. Once an approximate underlying steady flow is inferred from MWR and JunoCam data, another deeper layer can be proposed to enable that inferred and assumed steady flow pattern. Such a deeper flow might host a rotationally symmetrical zonal flow that is suggested by observations of Jupiter's lower latitudes. The three-layer extension of the model starts with members of the family of rotationally symmetrical zonal flows, and attempts to infer a member that is suitable to induce an overlying fluid layer that resembles the CPC cluster that was previously assumed as an underlying steady flow to explain MWR and JunoCam data, see Figure 3. Figure 3: A three-layer fluid-dynamical model with a rotationally symmetrical flow in layer 0 shown in the left panel. This layer induces a structure of CPCs (blue) with anticyclonic (orange) cores as shown in layer 2 in the right panel via an intermediate layer 1 as shown in the center panel. For stable CPCs to form from a rotationally symmetrical zonal flow, a cylonic annulus with anticyclonic borders is required. The induced overlying layer will develop a cluster of CPCs if the coupling is adjusted to a suitable range. The number of CPCs is related to the width of the annulus, and depends to some degree on its structure in detail.For a counter-rotating core to form and to be kept stable, the cyclonic annulus is best split into two with a suitable anticyclonic annulus inserted. Once the cyclones form in the overlying layer, they develop an anticyclonic core, if their centers happen to be located above the inserted anticylconic annulus. The modeled vorticity flux will accumulate anticyclonic vorticity in the core of the CPC from underneath.Anticyclones can form between the north polar cyclone and the CPCs, if the shielding of the polar cyclone is modeled in the bottom-most layer as an anticyclonic annulus that is separated from the polar vortex.The north polar cyclone needs to be shielded at some point within the polygon enclosed by the centers of the CPCs since otherwise the enclosed circulation would induce a net zonal CPC drift, see Figure 4a. Figure 4a: A cyclonic solid body vortex shielded by an anticyclonic annulus. Its radius can vary between that of the solid body vortex and that of the inner shielding of the cylconic annulus.b: Model with two to three anticyclones forming from an underlying anticyclonic ring inside the CPC cluster. The degree of freedom can be used to model an annulus that induces the formation of two or more large anticyclones, as shown in Figure 4b. Distinct morphological structures within the CPCs tend to develop from an annular structure more naturally if the annuli of cyclonic and anticyclonic vorticity are separated more distinctly than based on a Gaussian-like cross section of their stream function, see Figure 5a. Figure 5a: An underlying steady flow with sharply defined annuli induces distinct structures.b: An underlying steady flow that induces FFR-like flow. Simulated structures resembling folded filamentary regions (FFRs) tend to form if the underlying concentric annuli structure does not show a sufficiently clear excess of cyclonic vorticity together with a border of shielding anticyclonic vorticity as a function of radius, as illustrated in Figure 5b. In that case, local chaotic turbulence tends to form easier than a distinct filament...

Juno continues to observe the evolution of Jupiter’s circumpolar cyclones (CPCs) with JunoCam, JIRAM camera/spectrometer, and the Microwave Radiometer. The CPCs have distinctive cloud features, and unique characteristics that, at least in visible and infrared wavelengths, broadly classify into two morphological forms, “filled,” and “chaotic” as in Tabataba-Vakili et al. 2020. We call the chaotic form “spiral” (Fig. 1). As revealed by JunoCam, the filled CPCs typically appear with large, visibly bright features on the periphery, similar in appearance to a circular saw blade. Just inward, a nearly uniform darker region appears, occasionally displaying small hole-like openings, appearing bright at 5 μm. These darker regions (e.g., Fig. 1 left, CPC #3 & Fig. 2 left) are probably a result of flat, generally non-convective stratiform clouds. The overall appearance of the periphery and just inward is reminiscent of shear-like instability in the flow, distorting the flow into the “blade-like” shapes. Anticyclonic circulation has been witnessed in the center of several filled CPCs. Lightning has also been observed by JunoCam in one of the blade-like cloud features during PJ 31, and we occasionally observe thin, bright curvilinear cloud features and clusters of bright clouds with shadows indicating vertical structure.The spiral CPCs (Fig. 3), including the central, north polar cyclone have a different morphology than the filled cyclones, appearing as flocculent and tightly wrapped series of alternatively bright and darker spirals. Interestingly, CPC #2 has partially transformed from a chaotic morphology into a filled morphology, similar perhaps to how oval cyclones and barges in the low latitudes can sometimes transform into folded-filamentary cyclones (e.g., Clyde’s Spot; Hueso et al. 2022). Microwave radiometry strongly suggest that the north polar cyclone (NPC) is a third class of polar cyclone that morphologically appears as a spiral type but has a different vertical brightness temperature structure than possessed by any of the CPCs.This work documents the cloud-top structure of Jupiter’s polar cyclones, their changes, and their positions, which extends the results in Tabataba-Vakili et al. 2020. High resolution modeling seeking to understand the dynamical mechanisms driving the distinct morphologies will require detailed observational “ground-truths,” which this work provides.

A zonal flow pattern is well-established for Jupiter's lower latitudes. At high latitudes, this patterm breaks down as observed in visible-light, infrared, and much of the radio-wave spectrum. But around each pole, Juno's instruments observe a cluster of circumpolar cyclones (CPC) that appears to remain essentially stable over at least six years. A heavily simplified multilayer fluid dynamical model suggests that such a pattern may be able to form in overlying atmospheric layers from an underlying zonal flow pattern.Juno's wide-angle visible-light imager, JunoCam, continues to observe Jupiter's north polar region on a regular basis during each perijove flyby. As it is now northern summer on Jupiter, JunoCam with its wide field of view can see a little more than half of the northern CPCs. While locally the CPCs can change substantially, the overall octagonal pattern remains mostly stable.An attempt to model such a CPC pattern with an incompressible 2D Euler flow numerical model can maintain such a pattern temporarily. But it shows several caveats in detail. Several questions remain: Why is the northern CPC pattern octagonal? Why is it stable? How did it form? Why are there counter-rotating cores in some of the CPCs? Why are many of the CPCs of an almost circular shape? Why are there two distinct morphologies, i.e., filled and spiral? Friction with an underlying steady flow can modify a 2D Euler flow in such a way that anticyclonic vorticity can form inside a cyclone. But explaing the CPC pattern itself appears hard with such a two-layer model. However, the approach can be generalized in a computationally feasible way: Couple the 2D Euler flow tightly enough to the underlying steady flow such that it converges to a steady flow itself, and start with this new steady flow iteratively the same way. In this way, only one 2D fluid layer requires to be simulated at a time, but still an arbitrary number of layers can be simulated.This approach turns out to morph an axially symmetrical steady zonal flow with only small fluctuations into a CPC pattern when traversing the layers from bottom to top. Since each layer becomes essentially a steady flow, the CPC pattern ends up stable for any given modelled fluid layer of interest. We can think of portions of the time axis being translated into the vertical z-axis. It is those portions that change the flow pattern. A more chaotic flow can be achieved by reducing the coupling between layers. The simplification to the one-way effect of the coupling between layers is assumed to be justified by the density gradient.

In this work, we analyse data from the Jovian Infrared Auroral Mapper (JIRAM) imaging spectrometer on board the NASA mission Juno, to investigate the presence of spectrally identifiable ammonia clouds (SIACs). Focusing on the data from the first perijove passage, we found that a white vortex structure near 40 $^{\circ }$N provides the best candidate. Implementing atmospheric retrieval thanks to the planetary spectrum generator, we fit the JIRAM spectra (in the 2.5–3.1 $\mu$m range) inside and outside the vortex, varying the gaseous ammonia profiles, and the clouds and hazes properties and composition. We found that outside the vortex, the best fit is achieved using main clouds composed of tholins (approximation of an unknown contaminant material). Inside the vortex the best fit is achieved when main cloud decks are composed of pure ammonia ice, or ammonia-coated tholins. We therefore claim the detection of 38 SIACs, all detected over the white vortex structure. With respect to the external regions, the retrieved parameters distributions inside the vortex show: (i) higher altitude hazes and clouds, (ii) smaller haze’s effective radii, and (iii) higher gaseous ammonia relative humidity values. Both the detection of pure ammonia ice clouds and the retrieved physical parameters are consistent with the vortex being the result of a moist convection storm that uplifted fresh ammonia from the deep troposphere which in turn either condensed or became a possible source of coating material for existing cloud particles. This work confirms the trend established by space and ground-based observations, for which ammonia clouds on Jupiter are rare and connected to strong convective episodes.

Juno's close approach of Io, during the inbound branch of the Perijove-57 Jupiter flyby, allowed Juno's visible light imager, JunoCam, to take a short sequence of close-up Io images at a cadence of about one minute. Consecutive images cover overlapping areas on Io from different angles. The parallax effect is definitely perceptible for several of the highest mountains. The images also show shadows cast by some of the mountains onto their much flatter surroundings. Varying shading, to be distinguished from albedo and color variability, returns small-scale inclination data. Mountains imaged near Io's limb reveal distinctive silhouettes. We use all these ingredients to retrieve relative elevation data from JunoCam's close-up Io images. We will summarize the available data, the applied methods, and our derived digital terrain results.

Last year, we showed that JunoCam images, acquired in the visible, have the resolution necessary to measure the height of clouds from their projected shadows. We focused our analysis on the “Nautilus”, a 3000-km cyclonic vortex seen during Juno’s 14th periojove. That structure consists mainly of a spiraling counter clockwise white cloud that casts a shadow onto a reddish cloud deck∼20 to 30 km below. Small individual clouds also pop out of the white cloud deck, towering about ~10 to 20 km above it. An analysis of near-simultaneous HST images of the Nautilus confirms that the white region is higher than its surrounding darker, reddish cloud deck. These respective elevations are consistent with the white clouds being made of fresh ammonia ice while most of the reddish clouds underneath are made of ammonium hydrosulfide NH4SH, as predicted by equilibrium cloud models.An analysis by F. Biagiotti of a similar region observed by JIRAM during Juno’s 1st perijove identifies the presence of elusive ammonia ice crystals, either pure or mixed with a nitrogen-bearing species similar to Titan’s tholins. In addition, these clouds have altitudes that are consistent with the above interpretation. However, the surrounding material is not much deeper and incompatible with NH4SH. We discuss a possible solution to the corundum: At least in the gas, the atmosphere's optical thickness is much larger at the wavelengths used for the JIRAM study (2 to 3.2 micron) than in the visible. The effect of scattering by cloud particles is to be evaluated, but it appears likely that altogether, infrared observations at these wavelengths cannot penetrate as deep as visible ones.An interpretation of these observations, consistent with spectroscopic observations in the visible, is therefore that, at least in this region close to ~40°N, most of Jupiter's visible cloud deck is made of NH4SH, that updrafts can locally deliver fresh ammonia ice but that these ammonia ice crystals remain only for a short time either because of downwelling and evaporation or because of coating.