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The electromagnetic coupling between the Galilean satellites at Jupiter and the planetary ionosphere generates an auroral footprint, which is detected with high spatial resolution in the infrared L band by the Jovian InfraRed Auroral Mapper (JIRAM) onboard the Juno spacecraft. We report the JIRAM data acquired since 27 August 2016 until 23 May 2022, which are used to compute the average position of the footprint tracks of Io, Europa and Ganymede. The result of the present analysis help to test the reliability of magnetic field models, to calibrate ground‐based observations and to highlight the variability in the footprint positions, which can be used to probe the plasma environment at the orbit of the satellites. The determination of the plasma properties around the moons is particularly relevant to complement the Juno flybys of the moons during its extended mission, and to support the future Juice and Europa Clipper missions. Lastly, we report no clear evidence of the auroral footprint of Callisto, which is likely due to a combination of its low expected brightness and its position very close to the main Jovian aurora. Plain Language Summary: The Jovian InfraRed Auroral Mapper onboard the Juno spacecraft around Jupiter has now been gathering 6 years of observations. Here, we report the position of the auroral infrared emission associated with the orbital motion of Io, Europa and Ganymede. The position of this emission ‐ called footprint ‐ carries information on the magnetic field geometry and the distribution of charged particles along the magnetic field. Therefore, the footprint tracks provided here can be used to test and constrain magnetic field models, and to improve the calibration of ground based observations of Jupiter: this can help better understand the source region of the main Jovian aurora and its variations. Lastly, by surveying the data acquired over 40 Juno orbits, we point out variations in the footprint position, which reflect the variability in the plasma conditions near the moons: this monitoring may help determine the mass loading of the magnetosphere, which affects the intensity of the main aurora. The possibility of investigating the plasma environment at the orbit of the satellites is important to complement the satellite flybys performed during the extended mission of Juno and to support the future Juice and Europa Clipper missions, which are dedicated to the Galilean moons. Key Points: The position of the Io, Europa and Ganymede footprints based on Juno‐JIRAM observations are reported with unprecedented spatial resolutionThe positions of the footprints support the Juno‐based magnetic field models and the calibration of ground‐based observationThe transversal shift of the Ganymede footprint suggests variations of the plasmadisk; the shift appears to be correlated with local time [ABSTRACT FROM AUTHOR]

One of the auroral features of Jupiter is the emission associated with the orbital motion of its moon Io. The relative velocity between Io and the surrounding plasma trigger perturbations that travels as Alfvén waves along the magnetic field lines toward the Jovian ionosphere. These waves can accelerate electrons into the atmosphere and ultimately produce an auroral emission, called the Io footprint. The speed of the Alfvén waves—and hence the position of the footprint—depends on the magnetic field and on the plasma distribution along the field line passing through Io, whose SO2‐rich atmosphere is the source of a dense plasma torus around Jupiter. Since 2016, the Jovian InfraRed Auroral Mapper (JIRAM) onboard Juno has been observing the Io footprint with a spatial resolution of ∼few tens of km/pixel. JIRAM detected evidences of variability in the Io footprint position that are not dependent on the System III longitude of Io. The position of the Io footprint in the JIRAM images is compared with the position predicted by a model of the Io Plasma Torus and of the magnetic field. This is the first attempt to retrieve quantitative information on the variability of the torus by looking at the Io footprint. The results are consistent with previous observations of the density and temperature of the Io Plasma Torus. However, we found that the plasma density and temperature exhibit considerable non‐System III variability that can be due either to local time asymmetry of the torus or to its temporal variability. Key Points: Juno‐JIRAM detected evidence of variability in the Io footprint that are not related to the System III longitude of IoQuantitative information on the state of the Io Plasma Torus and its variability are inferred from the Io footprint positionThe Io Plasma Torus electron density varies between <2,000 and ∼2,750 cm−3, while the thermal ion temperature varies between 40–100 eV [ABSTRACT FROM AUTHOR]

In this work, we present the detection of CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ emissions in the equatorial atmosphere of Jupiter as two well‐separated layers located, respectively, at tangent altitudes of about 200 and 500–600 km above the 1‐bar level using the observations of the Jovian InfraRed Auroral Mapper (JIRAM), on board Juno. This provides details of the vertical distribution of H3+ ${\mathrm{H}}_{3}^{+}$ retrieving its Volume Mixing Ratio (VMR), concentration, and temperature. The thermal profile obtained from H3+ ${\mathrm{H}}_{3}^{+}$ shows a peak of 600–800 K at about 550 km, with lower values than the ones reported in Seiff et al. (1998), https://doi.org/10.1029/98JE01766 above 500 km using VMR and temperature as free parameters and above 650 km when VMR is kept fixed with that model in the retrieval procedure. The observed deviations from the Galileo's profile could potentially point to significant variability in the exospheric temperature with time. We suggest that vertically propagating waves are the most likely explanation for the observed VMR and temperature variations in the JIRAM data. Other possible phenomena could explain the observed evidence, for example, dynamic activity driving chemical species from lower layers toward the upper atmosphere, like the advection‐diffusion processes, or precipitation by soft electrons, although better modeling is required to test these hypothesis. The characterization of CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ species, simultaneously observed by JIRAM, offers the opportunity for better constraining atmospheric models of Jupiter at equatorial latitudes. Plain Language Summary: The Jovian Infrared Auroral Mapper (JIRAM) is the infrared imager and spectrometer on board the Juno mission, designed to investigate Jupiter's atmosphere. A key objective of JIRAM is the investigation of the minor species, such as CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ that are very important to understanding the energy balance of the middle and upper atmosphere of Jupiter. These species have strong signatures in the 3.3–3.8 μm spectral region, well within the nominal wavelength range of the instrument. We present the analysis of recent images and spectra obtained by JIRAM, in the period December 2018–September 2020, plus additional measurements in March 2017, to study methane and H3+ ${\mathrm{H}}_{3}^{+}$ vertical distribution at equatorial latitudes. We find that CH4 is localized around 200 km above the 1‐bar level, while a distinct layer of H3+ ${\mathrm{H}}_{3}^{+}$ is observed around 500–600 km (0.04–0.016 μbar). The observed vertical distribution and intensity variation of H3+ ${\mathrm{H}}_{3}^{+}$ is likely to be the result of vertically propagating waves. However, other possible phenomena can be invoked to explain these findings, like for example, an uplifting of chemical species from lower layers toward the upper atmosphere, or soft electrons precipitation, although a rigorous modeling is needed to confirm the latter hypothesis. Key Points: Detection of CH4 and H3+ ${\mathrm{H}}_{3}^{+}$ emissions over Jupiter's disc as two well separated layers in the equatorial region at 200 and 600 kmThe H3+ ${\mathrm{H}}_{3}^{+}$ temperature profile shows a peak of 600–800 K at about 600 km with some differences with respect to the Galileo's profileThe observed features point out the presence of localized variability with altitude, perhaps indicative of wave activities [ABSTRACT FROM AUTHOR]

The regular polygons of circumpolar cyclones, discovered by Juno in 2017, are one of the most puzzling features of Jupiter. Here we show new recent global pictures of the North polar cyclones' structure. These are the first simultaneous images of the whole structure since 2017, and we find that it remained almost unperturbed, just like the South one. The observation of these long‐lasting structures poses questions regarding the formation mechanism of cyclones, and on their vertical structure. Data by Juno/JIRAM infrared camera collected over the last 5 years show that cyclones migrate around what may seem like equilibrium positions, with timescales of a few months but, aside from that, the cyclones systems are very stable. Our analysis of the observations shows that the motion of cyclones around their equilibrium position is uncorrelated with their position if a barotropic approximation (β‐drift) is assumed. Thus, a different dynamical explanation than the barotropic β‐drift is needed to explain the stability of the observed features. Each cyclone has a peculiar morphology, which differs from the others and is stable over the observed lapse of time in most cases. Plain Language Summary: In 2017, Juno discovered that the poles of Jupiter are occupied by regular polygons of cyclones. Here we report 5 years of observations of these cyclones by JIRAM, the infrared imaging spectrometer on board Juno. In particular, we show the latest observations of the North Pole cyclones structure. In fact, this structure has only been partially observed since its discovery 5 years ago. One important question is how these structures of cyclones form, and if they are stable. We find that both remained almost unperturbed. Hence, we show that these cyclones may have very long lifetimes. Cyclones migrate around what may appear to be equilibrium positions. The scale time is a few months. We analyzed the movement of cyclones and compared it with a model where winds don't change with depth (a barotropic model). We found that the motion of the cyclones is not related to their position according to this model. We conclude that a different model is needed to explain some of the observed characteristics. Each cyclone has a peculiar morphology, which differs from the others and is stable over the observed time span in most cases. Key Points: For the first time after 5 years, we show a global picture of the North polar cyclones' structure, which has remained almost unperturbedEach cyclone has a peculiar morphology, which differs from the others and it is stable over the observed lapse of timeBeta‐drift is not responsible for the motion of the vortices on timescales of months [ABSTRACT FROM AUTHOR]

The Jovian InfraRed Auroral Mapper (JIRAM) onboard the NASA Juno mission monitored the evolution of Jupiter's polar cyclones since their first observation ever in February 2017. Data acquired by JIRAM have revealed cloudy cyclones organized in a complex, yet stable geometrical pattern at both poles. Several studies have investigated the dynamics and the structure of these cyclones, to understand the physical mechanisms behind their formation and evolution. In this work, we present vorticity maps deduced from the wind fields for the region poleward of ∼−80°, which has been extensively covered over the last four years of observations. The cyclonic features related to the stable polar cyclones are embedded in a slightly, but diffused anticyclonic circulation, in which short‐living anticyclones emerge with respect to the surroundings. Although the general stability of both the cyclones and the whole system is strongly confirmed by this work, variations in the shape of the vortices, as well as changes in the local structures, have been observed. Plain Language Summary: The Jovian InfraRed Auroral Mapper is the instrument onboard the NASA Juno spacecraft that has provided observations of Jupiter's poles since February 2017. These data have shown cyclones organized in snowflake‐like structures. The Jupiter's polar cyclones are long‐lasting features, which did not disappear or merge during 4 years of observations. In general, the analysis of the winds is important in the study of the cyclones. In this work, we focus on the vorticity, a quantity derived by the winds, that gives information on the magnitude and direction of the rotation of the cyclones. We focused on the southern polar region, which has a better coverage in time, with respect to the northern counterpart. The general pattern of the southern polar cyclones is preserved along the observations. Key Points: The vorticity field of Jupiter's southern polar cyclones is evaluated for different orbitsThe temporal variability of the vorticity field of the central polar cyclone is analyzedWe found extremely long stability of the morphology of circumpolar cyclones both in terms of clouds and winds [ABSTRACT FROM AUTHOR]

Juno discovered the circumpolar cyclones polygons on Jupiter in 2017. Fundamental questions regarding Jovian cyclogenesis concern the formation mechanism and whether these cyclones are deep or shallow. Recent data by Juno/JIRAM infrared camera show that any change is an extremely unlikely event on an annual scale. Only once, in 2019, a sixth cyclone joined the pentagonal structure in the South, but it disappeared after 2 months without merging with the pre‐existing cyclones; disappearance or creation of stable cyclones has never been observed. Additionally, the rotation speeds of the north and south polygons as a whole are not compatible with the shallow hypothesis; both structures drift at a much smaller rate than the typical scale velocities on Jupiter surface, and differ at the two poles. Cyclones oscillate around what may seem like equilibrium positions, and these oscillations tend to propagate from one cyclone to another. These oscillations have almost equal timescales, and here we investigate the possible implications of such similarity. Plain Language Summary: Juno/JIRAM performed four year of observations of the circumpolar structures at Jupiter. We investigate three major properties of these structures: they spin slowly, but at different rates, the South one being twice as fast as the North one; both structures as a whole, and the 15 singular cyclones are extremely stable; the cyclones have similar intrinsic oscillation frequencies, and perturbations seem to propagate from one cyclone to the closer one. Key Points: Juno performed 4 years of observations of the Jupiter polar cyclones. We discuss implications for their stability and vertical structureThe cyclones have similar intrinsic oscillation frequencies, and perturbations seem to propagate from one cyclone to the closer oneCyclones are extremely stable, individually and as a whole; they slowly spin and the South one is twice as fast as the North one [ABSTRACT FROM AUTHOR]

We analyse spectra measured by the Jovian Infrared Auroral Mapper (JIRAM, a payload element of the NASA Juno mission) in the 3150–4910 cm−1 (2.0–3.2  μ m)  range during the perijiove passage of 2016 August. Despite modelling uncertainties, the quality and the relative uniformity of the data set allow us to determine several parameters characterizing the Jupiter's upper troposphere in the latitude range of 35°S–30°N. Ammonia relative humidity at 500 millibars varies between 5 per cent to supersaturation beyond 100 per cent for about 3 per cent of the processed spectra. Ammonia appears depleted over belts and relatively enhanced over zones. Local variations of ammonia, arguably associated with local dynamics, are found to occur in several locations on the planet (Oval BA, South Equatorial Belt). Cloud altitude, defined as the level where aerosol opacity reaches unit value at 3650 cm−1 (2.74  μ m), is maximum over the Great Red Spot (>20 km  above the 1 bar  level) and the zones (15 km),  while it decreases over the belts and towards higher latitudes. The aerosol opacity scale height suggests more compact clouds over zones and more diffuse clouds over belts. The integrated opacity of clouds above the 1.3-bar pressure level is found to be minimum in regions where thermal emission of the deeper atmosphere is maximum. The opacity of tropospheric haze above the 200-mbar level also increases over zones. Our results are consistent with a Hadley-type circulation scheme previously proposed in literature for belts and zones, with clear hemisphere asymmetries in cloud and haze. [ABSTRACT FROM AUTHOR]

The Jovian InfraRed Auroral Mapper (JIRAM) on board the NASA Juno spacecraft is a dual‐band imager and spectrometer in the 2–5 μm range with 9‐nm spectral sampling, primarily designed to study the Jovian atmosphere and aurorae. In addition to these goals, JIRAM is used to obtain images and spectra of the Galilean satellites, every time the spacecraft attitude is favorable. Here we present JIRAM images and spectra of Ganymede obtained during the first 4 years of the mission. In particular, on 26 December 2019, during a relatively close passage of Juno with the moon, a dedicated reorientation of the spacecraft was performed to achieve optimized observations of Ganymede by Juno's remote sensing instruments, including JIRAM. In the outbound phase of the flyby, observing the northern polar regions of Ganymede at a distance of roughly 100,000 km, JIRAM collected infrared images and spectra of the surface at a spatial resolution as high as 23 km per pixel, covering high northern latitudes that were scarcely mapped previously. A photometric model of Ganymede reflectance is produced, which diverges from the Lambert model. The spatial distribution of the obtained spectra complements the available coverage of the surface, with particular regard to the 2.0‐µm water ice absorption band and, to a lesser extent, to the 4.26‐µm spectral feature diagnostic of CO2 trapped in water ice. The water ice distribution is compatible with sputtered‐induced water ice grain enrichment at high latitude (>45°). Several minor species (hydrated salts, trapped H2, CO2, and acids) are also identified in the measured spectra. Plain Language Summary: The Jovian Infrared Auroral Mapper (JIRAM) is a dual‐band imager and spectrometer on the NASA Juno spacecraft. It works in the range of 2–5 μm and its spectral sampling is 9 nm. JIRAM is mainly used to study the Jovian atmosphere and aurora. JIRAM is also used to obtain images and spectra of the moons of Jupiter, every time the spacecraft has a favorable attitude. Here, we show Ganymede images and spectra obtained during the first 4 years of the mission. On 26 December 2019, during a close passage of Juno to Ganymede, JIRAM observed it at a distance of approximately 100,000 km. In this occasion, JIRAM collected infrared images and surface spectra with a spatial resolution of up to 23 km per pixel. This data covers North polar regions that were not mapped before. A photometric model of Ganymede's reflectance was produced, and it is different from the Lambert model. The spatial distribution of the obtained spectrum can supplement the available coverage of the surface, especially for the 2.0 µm water ice absorption band. At high latitudes (>45°), the distribution of water ice is compatible with the enrichment of water ice particles induced by sputtering. Several minor species (hydrated salts, trapped H2, CO2, and acids) were also identified in the measured spectra. Key Points: Water ice distribution for previously unmapped regionsLatitudinal variability of CO2 spectral featureNew photometric model for Ganymede reflectance [ABSTRACT FROM AUTHOR]

The surface composition of Io is dominated by SO2 frost, plus other chemical species identified or proposed over the past decades by combining Earth‐based and space‐based observations with laboratory data. Here we discuss spectroscopic data sets of Io obtained by the Jovian InfraRed Auroral Mapper (JIRAM) spectro‐imager onboard Juno in nine orbits, spanning a 3‐year period. We display average spectral profiles of Io in the 2–5 μm range, and we use band depths derived from those profiles to map the geographic distribution of SO2 frost and other spectral features. This data set allows for an ~22% surface coverage at 58 to 162 km/px and in a broad range of latitudes. Our results confirm the broadly regional SO2‐frost trends already highlighted by Galileo/NIMS. Io's average spectral profiles as well as the mapping of the 4.47‐μm band also confirm that SO2 exists in the 32S16O18O isotopic form. Surprisingly, the mapping performed by JIRAM shows that the absorption band at 2.1 μm is unrelated to SO2 frost, while we map for the first time the depth of the 2.65‐μm band, highlighting regions enriched in this absorber, possibly H2S. JIRAM data confirm that the 3.92‐μm band, likely due to Cl2SO2, is largely related to the SO2 distribution. The correlation between Cl2SO2 and ClSO2, possibly revealed at 4.62 μm, is not equally clear. The simultaneous presence of two very weak spectral features at 4.55 and 4.62 μm suggests that nitrile compounds or tholins may also be present on the surface. Plain Language Summary: The surface of Io is mainly covered by sulfur dioxide (SO2) frost and by other chemical species. The Jovian InfraRed Auroral Mapper (JIRAM) instrument onboard the NASA Juno spacecraft, in orbit around Jupiter, can occasionally observe the Galilean satellites through its slit spectrometer (2–5 μm range). We show average spectral profiles of Io obtained by JIRAM in a 3‐year period, mapping the geographic distribution of SO2 frost and other spectral features. Our results confirm the broadly regional SO2‐frost trends already highlighted in the past. Our data confirm that SO2 exists in multiple isotopic forms. Surprisingly, the mapping performed by JIRAM shows that the absorption band at 2.1 μm is unrelated to SO2 frost. We map for the first time the depth of the 2.65‐μm band, which might be related to hydrogen sulfide (H2S). We also highlight regions enriched in this absorber. We confirm that the 3.92‐μm band, ascribed to sulfuryl chloride (Cl2SO2), is largely correlated with the SO2 distribution. The correlation between Cl2SO2 and ClSO2, possibly revealed at 4.62 μm, is not equally clear. The simultaneous presence of two very weak spectral features at 4.55 and 4.62 μm suggests that nitrile compounds or tholins may also be present on the surface. Key Points: We use spectra acquired by Juno/JIRAM in the range 2–5 μm over a 3‐year period, covering ~22% of Io, to map its surface compositionThe 2.1‐μm band and the 2.65‐μm band are unrelated with SO2 frost but display trends possibly related to the transport of volatilesWe confirm that the 4.47‐μm band is diagnostic of 32S16O18O, and we show that ClSO2 is not everywhere linked to the abundance of Cl2SO2 [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Juno has revealed extraordinary and unexpected dynamics in Jupiter's polar regions. The clouds imaged in the infrared and visible parts of the spectrum by JIRAM and JunoCam, respectively, are organized around a central cyclone in regular patterns of eight (North Pole) and five (South Pole) cyclones. We studied the spatial and temporal variability of the regions immediately outside the cyclonic circulations at the South Pole. By analyzing multiple JIRAM images at five microns, geographically merged and appropriately filtered and sampled, we found that cloud patterns poleward and equatorward the ring of cyclones at Jupiter's South Pole, may originate from flow instabilities not linked to vortices' dynamics. These instabilities can have their origin in the horizontal pressure and temperature gradients rather than in the cyclonic circulations and their interactions, also considering the low speed values of the wind field in those regions. Key Points: Dynamics consistent with quasi‐geostrophic 2‐D turbulence in the Jupiter South Polar regions surrounding the main cyclonic circulationsThe forcing scales resulting from these analyses indicate that baroclinic instabilities may exist in the analyzed regionsMany waves have been revealed in the Jupiter South Polar region by JIRAM images [ABSTRACT FROM AUTHOR]

We observed the evolution of Jupiter's polar cyclonic structures over two years between February 2017 and February 2019, using polar observations by the Jovian InfraRed Auroral Mapper, JIRAM, on the Juno mission. Images and spectra were collected by the instrument in the 5‐μm wavelength range. The images were used to monitor the development of the cyclonic and anticyclonic structures at latitudes higher than 80° both in the northern and the southern hemispheres. Spectroscopic measurements were then used to monitor the abundances of the minor atmospheric constituents water vapor, ammonia, phosphine, and germane in the polar regions, where the atmospheric optical depth is less than 1. Finally, we performed a comparative analysis with oceanic cyclones on Earth in an attempt to explain the spectral characteristics of the cyclonic structures we observe in Jupiter's polar atmosphere. Plain Language Summary: The Jovian InfraRed Auroral Mapper (JIRAM) is an instrument on‐board the Juno NASA spacecraft. It consists of an infrared camera, for mapping both Jupiter's auroras and atmosphere, and a spectrometer. In February 2017, the complex cyclonic structures that characterize the Jupiter's polar atmospheres were discovered. Here, we report the evolution of those cyclonic structures during the 2 years following the discovery. We use for this purpose infrared maps built by the JIRAM camera images collected at wavelengths around 5 μm. The cyclones have thick clouds that obstruct most of the view of the deeper atmosphere. However, some areas, near the cyclones, are only covered by thin clouds allowing the spectrometer to see deeper in the atmosphere. In those areas, the instrument was able to detect spectral signatures that permitted estimation of abundances of water vapor, ammonia, phosphine, and germane. Those gases are minor but significant constituents of the atmosphere. Finally, the dynamics of the Jupiter's polar atmosphere are not well understood and are still under study. Here, to suggest possible mechanisms that governs the polar dynamics, we attempted a comparative analysis with some Earth oceanic cyclones that show similarities with the Jupiter ones. Key Points: The Jupiter's polar cyclonic structures did not change much in two years of observations from February 2017 to February 2019Abundances of some atmospheric minor constituents measured in the hottest spots of the polar regions, higher values registered in the southEarth oceanic cyclones analogies suggest a well‐mixed upper boundary layer on Jupiter's Poles [ABSTRACT FROM AUTHOR]

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 <1% to over 15%. At intermediate latitudes (30–70°) the water vapor maxima are associated with the location of cyclonic belts, as inferred from mean zonal wind profiles (Porco et al., 2003). The high‐latitude regions (beyond 60°) are drier in the north (mean relative humidity around 2–3%) than the south, where humidity reaches 15% around the pole. The ammonia volume mixing ratio varies from 1 × 10−4 to 4 × 10−4. A marked minimum exists around 10°N, while data suggest an increase over the equator. The high‐latitude regions are different in the two hemispheres, with a gradual increase in the south and more constant values with latitude in the north. The phosphine volume mixing ratio varies from 4 × 10−7 to 10 × 10−7. A marked minimum exists in the North Equatorial Belt. For latitudes poleward 30°S and 30°N, the northern hemisphere appears richer in phosphine, with a decrease toward the pole, while the opposite is observed in the south. JIRAM data indicate an increase of germane volume mixing ratio from 2 × 10−10 to 8 × 10−10 from both poles to 15°S, with a depletion centered around the equator. Arsine presents the opposite trend, with maximum values of 6 × 10−10 at the two poles and minima below 1 × 10−10 around 20°S. Key Points: Horizontal variations of gases are dominated by latitudinal components; longitudinal variations are relatively more important for waterPhosphine and germane abundances fit well the model of disequilibrium species transported upward from deep troposphere by vertical mixingStrong upturn of arsine at polar latitudes seen by JIRAM cannot be explained by the diffusion‐kinetics model [ABSTRACT FROM AUTHOR]

The instrument JIRAM (Jovian Infrared Auroral Mapper), on board the NASA spacecraft Juno, is both an imager and a spectrometer. Two distinct detectors are used for imaging and spectroscopy. The imager acquires Jupiter images in two bands, one of which (L band, 3.3–3.6 μm) is devoted to monitor the H3+ emission. The spectrometer covers the spectral region from 2 to 5 μm (average spectral resolution 9 nm) with a 256 pixels slit that can observe the same scene of the L band imager with some delay. JIRAM scientific goals are the exploration of the Jovian aurorae and the planet's atmospheric structure, dynamics and composition. Starting early July 2016 Juno is orbiting around Jupiter. Since then, JIRAM has provided an unprecedented amount of measurements, monitoring both Jupiter's atmosphere and aurorae. In particular, the camera has monitored Jupiter's poles with very high spatial resolution, providing new insights in both its aurorae and the polar dynamic. The main findings obtained by the L imager are detailed pictures of Jupiter's aurorae showing an extremely complex morphology of the H3+ distribution in the main oval and in the moon's footprints. The spectrometer has enabled the measure the distribution of both H3+ concentration and temperature. The analysis of the north auroral region limb observations shows that the peak density of H3+ is above 750 km and that often it is anticorrelated to the temperature, confirming the infrared cooling effect of H3+. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'. [ABSTRACT FROM AUTHOR]

Abstract: We present wind speeds at the ~ 1 bar level at both Jovian polar regions inferred from the 5‐μm infrared images acquired by the Jupiter InfraRed Auroral Mapper (JIRAM) instrument on the National Aeronautics and Space Administration Juno spacecraft during its fourth periapsis (2 February 2017). We adopted the criterion of minimum mean absolute distortion (Gonzalez & Woods, 2008) to quantify the motion of cloud features between pairs of images. The associated random error on speed estimates is 12 m/s in the northern polar region and 9.8 m/s at the south. Assuming that polar cyclones described by Adriani et al. (2018, https://doi.org/10.1038/nature25491) are in rigid motion with respect to System III, tangential speeds in the interior of the vortices increase linearly with distance from the center. The annulus of maximum speed for the main circumpolar cyclones is located at approximatively 1,000 km from their centers, with peak cyclonic speeds typically between 80 and 110 m/s and ~50 m/s in at least two cases. Beyond the annulus of maximum speed, tangential speed decreases inversely with the distance from the center within the Southern Polar Cyclone and somewhat faster within the Northern Polar Cyclone. A few small areas of anticyclonic motions are also identified within both polar regions. [ABSTRACT FROM AUTHOR]

The familiar axisymmetric zones and belts that characterize Jupiter's weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes. Two-dimensional turbulence in combination with the Coriolis β-effect (that is, the large meridionally varying Coriolis force on the giant planets of the Solar System) produces alternating zonal flows. The zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on Jupiter can occur. Simulations with shallow-water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles. Jovian polar regions are not visible from Earth owing to Jupiter's low axial tilt, and were poorly characterized by previous missions because the trajectories of these missions did not venture far from Jupiter's equatorial plane. Here we report that visible and infrared images obtained from above each pole by the Juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones are observed about a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Cyclonic circulation is established via time-lapse imagery obtained over intervals ranging from 20 minutes to 4 hours. Although migration of cyclones towards the pole might be expected as a consequence of the Coriolis β-effect, by which cyclonic vortices naturally drift towards the rotational pole, the configuration of the cyclones is without precedent on other planets (including Saturn's polar hexagonal features). The manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the strong unidentified emission near 3.28 μm in Titan's upper daytime atmosphere recently discovered by Dinelli et al. We have studied it by using the NASA Ames PAH IR Spectroscopic Database. The polycyclic aromatic hydrocarbons (PAHs), after absorbing UV solar radiation, are able to emit strongly near 3.3 μm. By using current models for the redistribution of the absorbed UV energy, we have explained the observed spectral feature and have derived the vertical distribution of PAH abundances in Titan's upper atmosphere. PAHs have been found to be present in large concentrations, about (2-3) × 104 particles cm-3. The identified PAHs have 9-96 carbons, with a concentration-weighted average of 34 carbons. The mean mass is ~430 u; the mean area is about 0.53 nm2; they are formed by 10-11 rings on average, and about one-third of them contain nitrogen atoms. Recently, benzene together with light aromatic species as well as small concentrations of heavy positive and negative ions have been detected in Titan's upper atmosphere. We suggest that the large concentrations of PAHs found here are the neutral counterpart of those positive and negative ions, which hence supports the theory that the origin of Titan main haze layer is located in the upper atmosphere. [ABSTRACT FROM AUTHOR]

We show how to obtain the first multipole contributions to the electromagnetic radiation emitted by an arbitrary localized source directly from the Jefimenko equation for the magnetic field and the Panofsky-Phillips equation for the electric field. This procedure avoids the unnecessary calculation of the electromagnetic potentials. [ABSTRACT FROM AUTHOR]

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright ‘dipole’ feature surrounded by a cold ‘collar’ at its north pole. The polar dipole is a ‘double-eye’ feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus’ south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. [ABSTRACT FROM AUTHOR]

The extent of springtime Arctic ozone loss does not reach Antarctic "ozone hole" dimensions because of the generally higher temperatures in the northern hemisphere vortex and consequent less polar stratospheric cloud (PSC) particle surface for heterogeneous chlorine activation. Yet, with increasing greenhouse gases stratospheric temperatures are expected to further decrease. To infer if present Antarctic PSC occurrence can be applied to predict future Arctic PSC occurrence, lidar observations from McMurdo station (78° S, 167° E) and Ny Ålesund (79° N, 12° E) have been analysed for the 9 winters between 1995 (1995/1996) and 2003 (2003/2004). Although the statistics may not completely cover the overall hemispheric PSC occurrence, the observations are considered to represent the main synoptic cloud features as both stations are mostly situated in the centre or at the inner edge of the vortex. Since the focus is set on the occurrence frequency of solid and liquid particles, the analysis has been restricted to volcanic aerosol free conditions. In McMurdo, by far the largest part of PSC observations is associated with NAT PSCs. The observed persistent background of NAT particles and their potential ability to cause denoxification and irreversible denitrification is presumably more important to Antarctic ozone chemistry than the scarcely observed ice PSCs. Meanwhile in Ny-Ålesund, ice PSCs have never been observed, while solid NAT and liquid STS clouds both occur in large fraction. Although they are also found solely, the majority of observations reveals solid and liquid particle layers in the same profile. For the Ny-Ålesund measurements, the frequent occurrence of liquid PSC particles yields major significance in terms of ozone chemistry, as their chlorine activation rates are more efficient. The relationship between temperature, PSC formation, and denitrification is nonlinear and the McMurdo and Ny-Ålesund PSC observations imply that for predicted stratospheric cooling it is not possible to directly apply current Antarctic PSC occurrence to the Arctic stratosphere. Future Arctic PSC occurrence, and thus ozone loss, is likely to depend on the shape and barotropy of the vortex rather than on minimum temperature alone. [ABSTRACT FROM AUTHOR]

The spectral responsivity shape plays an important role in the prospect of a wide use of broad-band meters in the UV-B monitoring. As most UV-B broad-band meters have a responsivity approximating an erythemal action spectrum, a measurement campaign was planned to verify if such an instrument could be successfully used to measure the unfiltered global irradiance. A Yankee radiometer mod. UV-B 1 and a Brewer spectrophotometer, considered as a reference meter, were compared for this purpose. A short theoretical treatment of the Yankee radiometer response and some results of the comparison are shown. Only clear-sky days data are selected so that the UV-B radiation reaching the ground could be modelled as the sum of the direct and the isotropic diffuse components. The comparison results show a good agreement between the two instruments and confirm the capability of a broad-band UV-B radiometer of correctly measuring the global irradiance. [ABSTRACT FROM AUTHOR]

We provide an elementary proof that the action for the physical trajectory of the one-dimensional harmonic oscillator is guaranteed to be a minimum if and only if s < p=x, where s is the elapsed time and x is the oscillator's natural frequency. [ABSTRACT FROM AUTHOR]

We give a simple argument to show that the nth wavefunction for the one-dimensional Schrödinger equation has n-1 nodes. We also show that if n12, then between two consecutive zeros of ψψn1 there is a zero of ψn2. [ABSTRACT FROM AUTHOR]