John H. Rogers

JUICE (JUpiter ICy moons Explorer) is the first large mission in ESA’s Cosmic Vision 2015-2025 programme. The spacecraft was launched on April 2023 and will arrive at the Jupiter system in July 2031. The primary science goals of the mission are to characterize the Jovian icy satellites, studying their surfaces and interiors to unveil their history and internal structures, and to assess the emergence of habitable environments in their internal oceans [1]. To reach those goals JUICE will perform a complex series of orbits around Jupiter in which it will also run an extensive series of observations of the planet’s atmosphere [2], its magnetosphere and the ring system. All previous Jupiter missions since Galileo have benefited from extensive ground-based campaigns with a variety of telescopes and observational capabilities. A brilliant example of those collaborations comes from NASA’s Juno mission, which has requested collaboration with amateurs for a full decade, enhancing the spatial context and investigations in the time domain of various instruments with a particular strong participation with the Juno camera [3]. In this regard, amateur observations of Jupiter have demonstrated the capability to provide an excellent coverage of atmospheric phenomena that serve as spatial and temporal context to the close observations from spacecraft instruments or space telescopes. Databases of amateur observations such as ALPO Japan (https://alpo-j.sakura.ne.jp/indexE.htm) and PVOL (http://pvol2.ehu.eus/) [4] serve the science community providing access to the amateur data. Open source software tools popular in the amateur community (WinJupos, available at https://jupos.org/) [5] or more python-oriented tools such as PlanetMapper [6] support the analysis of amateur data. In addition, ESA’s Planetary Science Archive (https://archives.esac.esa.int/psa/#/pages/home) releases public data obtained by the two monitoring cameras (JMC; Juice Monitoring Camera 1 and 2) and will soon release also data from the navigation camera (NAVCAM). Data from the science instruments will be released through ESA’s Planetary Science Archive after proprietary time.In this contribution, we discuss the interest of the mission and its Jupiter Atmosphere Working Group to receive observational support from amateur astronomers. This support is needed during the years before Juno and JUICE to continue understanding temporal changes in the atmosphere of the planet. During the JUICE mission, particular needs will arise over different periods. For example, over the first year of the mission JUICE orbits will be eccentric with larger apojoves implying longer periods of time between close perijoves. Later, orbits will have high-inclinations with reduced views of the equatorial latitudes and in the year before Ganymede orbit insertion orbits will be more regular but constrained by Data Volume. We expect that JUICE collaboration with amateur astronomers will broaden public involvement in the mission and will enhance outreach activities of the mission.With Jupiter having a negative declination over 2031-2035 when observed from Earth, observations from the southern hemisphere and equatorial latitudes will be favored. Thus, specific outreach activities targeting amateur astronomy in the Global South may improve the amateur collaboration in the mission. Jupiter’s south declination implies that amateur observers in Japan, European countries and the US, where most experienced observers actively participating in collaborations with Jupiter researchers reside, will observe Jupiter under low elevations. Thus, we will actively promote knowledge of the mission in South America and Africa, where amateur astronomy is popular but Jupiter observations are less frequent. We expect to identify JUICE science activities that can be promoted within partners such the Astronomical Society of Southern Africa, the Asociación Argentina Amigos de la Astronomía and Sociedad Astronómica de Valparaiso y Viña del Mar. Such activities can be fostered with the help and participation of international societies promoting astronomy worldwide. Key partners toward that effort are The Europlanet Society and the International Astronomical Union Outreach Group. We will also seek a global collaboration with traditional actors in the amateur planetary astronomy world including the British Astronomical Association Jupiter Section, the Association of Lunar and Planetary Observers and planetary imaging communities on well-known international forums such as Cloudy Nights.References[1] Grasset et al. JUpiter ICy moons Explorer (JUICE): An ESA mission to orbit Ganymede and to characterise the Jupiter system. Planetary and Space Science, 78 (2013). [2] Fletcher et al. Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer. Space Science Reviews, 219 (2023). [3] Hansen, C.J., et al. Junocam: Juno’s Outreach Camera. Space Sci Rev 213, 475–506 (2017). [4] Hueso et al. The Planetary Virtual Observatory and Laboratory (PVOL) and its integration into the Virtual European Solar and Planetary Access (VESPA). Planetary and Space Science, 150 (2018). [5] Jacquesson and Mettig. JUPOS: Amateur analysis of Jupiter images with specialized measurement software. European Planetary Science Congress (2008). [6] King and Fletcher, PlanetMapper: A Python package for visualizing, navigating and mapping Solar System observations. Journal of Open Source Software, 8 (2023).

Summary & IntroductionEpisodes of reddish or yellowish coloration of the Equatorial Zone (EZ), either in a broad Equatorial Band (EB) or more widely, have been noted throughout observational history [Ref.1]. More recently, a long-term survey at 5 microns by Antuñano et al. [Refs.2,3] has shown episodes of brightening, i.e. cloud clearance in the EZ (‘EZ disturbances’), which partially coincide with coloration episodes, and a periodicity of 6.6 (±0.5) years was proposed though some events were ‘missing’. Here we review the history of colorations since 1971 from amateur observations, so as to give a systematic account for comparison with the 5-mm data. This comparison reinforces the evidence for the 7-year period, and shows that this phenomenon has several dissociable aspects.Reddish coloration and/or darkening was present more often than not in the 1960s and 1970s, but episodes have been more distinct in other decades. From the 1990s onwards they are well documented by colour and colour-filter imaging, which gives objective data even though our descriptions are still largely subjective. While some episodes exhibit obvious yellow or orange or duller ochre colour, and can last for several years, other episodes show only a brownish-grey shade changing to neutral dark grey, and only last for 1-2 years. Some episodes begin with a pure yellow or orange colour, which then becomes darker and less saturated [Ref.1]. Coloration episodes since 1971Episodes up to 1991 were described in [Ref.1]. Subsequent episodes were described in the interim reports of the BAA Jupiter Section [https://britastro.org/sections/jupiter]. Figs.1 & 2 show examples of maps from amateur images, mostly made by M. Vedovato and R. Bullen. In the following description, 5-micron information after 1979 is from [Refs.2-4].1972-76: Pure yellow-orange colour during 1972, which then condensed into a massive dark brown or grey-brown EB including southern EZ while the SEB was whitened (1973-1975). It was grey in 1976, then faded away. (This massive belt was also 5-micron-bright from 1973-1976: Ref.5.)1977-82: Largely pure colour, strong yellow or ochre over most of EZ, but with grey EB component in 1978-79 and thereafter; then, yellow colour gradually retreating to EZ(S) and fading. (It was 5-micron-bright in 1979 [Ref.5]; no data in other years.)(1986: Although NEDFs and grey shadings were prominent, the EZ remained largely white so there was no coloration event. There was also no 5-micron event, pausing the 7-year periodicity.)1989-1992: Started as pure yellow colour in late 1989, becoming brown or (eventually) grey in 1990-92, with the colour shifting southwards. (5 micron coverage was not continuous, but EZ was still dark until 1991 May, then bright in 1992 Jan-April.)1999-2000: A brown EB developed in mid-1999, then became dark grey from 1999 Nov. to 2000 Jan. (At 5 microns, similar timecourse.)2006-2007: In 2006, dark features accumulated all across the EZ including a brown EB. In 2007, the whole EZ was largely grey-brown. It faded after July but brown EB was still present at some longitudes up to 2008 May. (At 5 microns, similar timecourse.)2012-2013: Orange colour in an EB from 2012 June to 2013 March, particularly in 2012 July-August, coinciding with the vigorous revivals of the NTB and NEB. Weak at some longitudes, and not methane-bright.2018-2022: Orange colour developed gradually in 2018 (March-May), and was intense in late 2018 and in 2019. It was fainter in early 2020 but revived in late 2020, and was intense during 2021. It faded away in the second quarter of 2022. (There was a weak 5-micron-bright EB in 2019 Jan., but otherwise only small weakly 5-micron-bright streaks from 2018 Aug. (not earlier) to 2021 [Ref.4; G. Orton et al., EPSC2022-761; G. Orton, pers.com.].)Stationary features in orange haze over EZ: During much of this episode, the orange EB was particularly bright in methane-band images, and we detected waves on its S edge (in 2020) and large methane-bright patches (in 2021) that were almost stationary in System III [J.Rogers & C.Go, EPSC2021-95]. This is unprecedented, and suggests that the orange, methane-bright haze extended up to very high altitude. 2024-2025: A grey-brown EB gradually appeared from 2023 Dec. onwards, and was notable in 2024-25; it faded away in 2025 Dec. (There was a partial 5-micron-bright EB for much of this time: G. Orton, pers.com.)Relation to 5-micron clearancesThese coloration episodes fit the cycle of ‘EZ disturbances’ with period of 6-7 years proposed in [Refs.2,3] on the basis of brightening in the thermal infrared at 5 microns. Neither these, nor visible reddish coloration, alone reveal a clear periodicity. But if we combine the record of dark brownish-grey episodes, orange or ochre episodes, and 5-mm clearances, the 6-7-year periodicity is consistent (Fig.3):_____________________________________________________________________________________________________The brown/grey episodes have lasted less than 2 years, coinciding with the 5-micron clearances, and are simply understood as substantial clearance of the main cloud deck producing both the low albedo and the bright thermal signal. The more vividly coloured episodes are more complex, and sometimes last for several years while the 5-micron clearance is much shorter or even (in 2012) does not occur at all. The orange coloration must be an additional aerosol, which Antuñano et al.[Ref.4] suggested was exposed by the removal of the upper clouds. Indeed it is not always methane-bright (e.g. 2012), but sometimes it is (1972; 2020-21), indicating higher altitude. The temporal coincidence and periodicity of these events imply that they are all part of one complex phenomenon, which can entail cloud clearance and/or orange aerosol formation in different proportions. References:[1] Rogers JH (1995) The Giant Planet Jupiter (Cambridge Univ. Press).[2] Antuñano A et al.(2018)....

For 20 years the hstjupiter mailing list has been the venue where amateur planetary imagers collaborate and support Planetary Astronomers in various field of research including space missions. The hstjupiter group had been the venue where several discoveries were first announced (ie several outbreaks in Jupiter and Saturn, Bird Strike, several impacts on Jupiter). This is also a venue where planetary astronomers request imagers for support. We will discuss the contributions of this mailing list and the future plans.

IntroductionThe Juno mission continues to expand its science goals beyond those of the prime mission and the first extended mission. Atmospheric studies will continue to be among Juno’s science goals and an area in which the world-wide community of Jupiter observers can provide significant contextual support. A series of radio occultation measurements derive vertical profiles of electron density and the neutral-atmospheric temperature over several atmospheric regions. Physical Details of the MissionFigure 1 shows the sequence of orbits and key investigations of the primary and extended missions.igure 1. Progression of Juno orbits viewed from above Jupiter’s north pole with respect to local time of day. “PJ” designates a “perijove”, the closest approach to Jupiter on each numbered orbit. Following a Ganymede flyby on PJ34 (green orbit), the orbital period decreased from 53 days to 43-44 days (green + blue orbits). The “Great Blue Spot” (blue) orbits map an isolated patch of intense magnetic field. Following a close Europa flyby on PJ45 (aqua orbit), the period decreased to 38 days (orange orbits). Following close flybys of Io on PJ57 and PJ58 (black orbits) the period decreased to 33 days (red orbits). In reflected sunlight, Jupiter mostly appears as a crescent at perijoves following PJ58, but closer to its original phase angle by P110.Some characteristics of perijoves of the extended mission for the year starting in September, 2026, are shown in Table 1. We caution that while the day of year for the perijoves is reasonably fixed, the exact times may change.Role of Amateur AstronomersWe’ve noted at previous EPSC and EPSC-DPS meetings how the amateur community can contribute to the Juno mission via their collective world-wide 24/7 coverage of Jupiter. This applies also to the cadre of professional astronomers supporting the Juno mission. For example, this community has provided the context of different regions over which Juno’s Microwave Radiometer (MWR) has sensed plumes and “hot spots” (Fletcher et al. 2020). They have also alerted observers to strong interactions between the Great Red Spot and smaller anticyclones (Sanchez-Lavega et al. 2021) and the occurrence and evolution of prominent and unusual vortices, such as “Clyde’s spot” (Hueso et al. 2022). The continued tracking of outbreaks in the southern part of the North Equatorial Belt (NEB) also greatly informed the Juno team and supporting astronomers regarding the systematic longitudinal distribution of outbreaks and the range of atmospheric features they generate. A perijove-by-perijove summary of Juno-supporting observations is available at the following web site: https://www.missionjuno.swri.edu/planned-observations.After PJ50, Juno’s perijoves migrated to the nightside. From now through the end of the mission, images from this community will be extremely useful to provide a context for several investigations, such as as the MWR measurements of thermal emission from the deep atmosphere that includes mid-to-high latitude coverage. Observations from the amateur community will also provide the visible-wavelength context for anticipated continuation of JIRAM’s 5-µm maps of much of the southern hemisphere. They will also support the Microwave Radiometer (MWR) observations. Finally, the observations will also provide contextual support for a series of measurements to determine a local temperature profile by tracking the phase shift in Juno’s high-gain antenna signal as the spacecraft goes behind Jupiter (known as “ingress”) and as it emerges from behind Jupiter (known as “egress”). Figure 2 summarizes graphically all of the successful and planned radio-occultation sequences.Some of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).We dedicate this work to the memory of Dr. Candice Hansen, who was the Juno instrument lead for JunoCam through most of the mission. She provided operational insight and guidance for both the public access to Juno observations envisioned for this instrument and for the strong quantitative scientific results it brought to the mission.Fletcher et al. 2020. J. Geophys. Res. 125, 306399.Hueso et al. 2022. Icarus 380,114994Sanchez-Lavega et al. 2021. J. Geophys. Res. 126, e006686.Table 1. Perijove properties for a portion of Juno’s extended mission for a year, covering PJ87-PJ98. Information for previous perijoves and a summary of observations at large telescopes is listed in: https://www.missionjuno.swri.edu/planned-observations.PJDateApprox. Spacecraft Event TimePJ lat. (centric)PJ long. (System III)Solar Elongation872026 Sep 905:1672°324°31°882026 Oct 1121:2573° 325°56°892026 Nov 1312:4373°296°85°902026 Dec 1604:1174° 272°118°912027 Jan 1719:3175°244°151°922027 Feb 1910:4375°210°171°932027 Mar 2401:5776°178°134°942027 Apr 2516:5076°133 °103°952027 May 2808:4877°127°73°962027 Jun 3000:2477°108°47°972027 Aug 117:0678°129°23°982027 Sep 309:1078°127°2°

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.

Sprawling, turbulent cloud formations dominate the meteorology of Jupiter's mid‐to‐high latitudes, known as Folded Filamentary Regions (FFRs). A multi‐wavelength characterization by Juno reveals the spatial distribution, vertical structure, and energetics of the FFRs. The cloud tops display multiple lobes of stratiform aerosols, separated by darker, cloud‐free lanes, and embedded with smaller eddies and high‐altitude cumulus clouds. These cyclonic FFRs are microwave‐bright in shallow‐sounding wavelengths ( bars) and microwave‐dark in deep‐sounding wavelengths ( bars), with the transition potentially associated with the water condensation layer (6–7 bars). Associating microwave contrasts with temperature anomalies, this implies despinning of cyclonic eddies above/below their mid‐planes. Despite deep roots (being detectable in wavelengths sounding bars), they are “pancake vortices” with horizontal extents at least an order of magnitude larger than their depth. In the northern hemisphere, FFRs are most common in cyclonic belts poleward of N (all latitudes are planetocentric), particularly a North Polar Filamentary Belt (NPFB) near N that defines the transition from organized belts/zones to the chaotic polar domain. This distribution explains the high lightning rates from N, peaking in a belt poleward of N, which may trace the availability of water for moist convection. Many observed lightning flashes can be associated to specific FFRs containing bright storms, but some FFRs display no activity, suggesting quiescent periods during storm evolution. Analogies to Earth's oceanic eddies suggest that cyclones deform isentropic surfaces at their midplanes, raising deep water‐rich layers upwards to promote moist convection, release latent heat, and inject clouds into the upper troposphere.

IntroductionJupiter’s northern Equatorial Zone (EZn) and southern North Equatorial Belt (NEBs) are dominated by three features: five-micron hotspots (seen as North Equatorial Dark Features, NEDFs, in the optical), white cloud plumes, and complex local circulation. These features are influenced by the NEBs jet, which is modulated by a meridionally trapped Rossby wave, in conjunction with the high concentration of ammonia in the EZ and the ammonia depletion in the NEB. Numerous measurements have been made of the temperature, aerosol, and ammonia distributions in this region (c.f. Fletcher et al., 2020). And a number of models have been partially successful at explaining the interrelationships between the observed features (c.f Showman & Dowling, 2000). Here we explore the ammonia and cloud height distribution during 2024-25, when NEDFs and five-micron hotspots were prominent, using the optical band-average technique (Hill et al., 2024, Irwin et al., 2025). We show that while many sensing methods highlight the ammonia and aerosol depletion in five-micron hotspots, this band average method highlights enhancements in ammonia to the south of the hotspots.ObservationsMultiple observations on 2025-01-06 were made allowing coverage of a wide range of longitudes and coverage of a given longitude at several zenith angles. Figure 1 shows maps constructed using the method of Hill et al. (2024). An empirical limb correction is applied in addition to a weighted averaging scheme for overlapping observations. The data clearly show that enhanced ammonia regions lie to the south of NEDFs (labeled 1-4 in order of ascending longitude). For the ammonia enhancements we observe a planetary wave number of nine, within the range of hotspot and NEDF wavenumbers typically observed.DiscussionThe NEBs jet speed peaks at about 7° N, which in fact marks the boundary between the NEDFs and the ammonia enhancements. Anticyclonic gyres are a known feature seen in the same location as we show ammonia enhancements (c.f. Choi et al., 2013). We hypothesize that these gyres are regions of uplift and outflow, bringing up ammonia rich air from deeper levels of the atmosphere. The NEDFs are thought to be areas of subsidence, with cyclonic flow, where dryer air descends from above and results in a clearing of aerosols. Figure 1D shows this schematically with upwelling occurring at the gyres, horizontal winds carrying condensates from the upwelling source to the east and northeast as the visible cloud plumes, and descending clear air in the NEDFs.To further support this hypothesis, we analyze the ammonia mole fraction and cloud pressure at the NEDFs, gyres, and in the plumes through a regions-of-interest (ROI) approach. Figure 2 shows a longitudinal subset of the data in Figure 1, focusing on ammonia regions 3 and 4. Rectangles outline the ROIs which are analyzed for three observation times in Figure 2A. Figure 2B shows a time series of average values at each observation time for cloud pressure and ammonia mole fraction along with statistical errors. Finally, 2C shows scatter plots of the average cloud pressure versus the ammonia abundance. Note the very clear clustering of points where the NEB sample provides a consistent reference with relatively high pressure and very low ammonia abundance. Following the upwelling ammonia, eastward advection of plume aerosols, and NEDF subsidence from Figure 1, we can trace an ammonia cycle between its gaseous source and sink, with an intermediary aerosol state.Future WorkHundreds of observations of NEDFs and ammonia enhancements in the EZn have been made in 2024-25 using the Hill et al. (2024) technique. This data set will be analyzed and assessed for the statistical consistency of the results presented here. In addition, this data set will be compared to complementary multispectral observations to help discriminate why the optical method seems to so clearly detect ammonia enhancements at the 1-2 bar pressure level and why these enhancements appear broad enough to overlap NEDFs.Figure 1. Ammonia mole fraction, cloud pressure, and visual context maps created from observations on 2025-01-06 using an 11 inch Schmidt-Cassegrain telescope. A) Ammonia mole fraction (ppm) with enhanced areas labeled 1-4 in order of ascending longitude. The black circle at left shows the approximate spatial resolution of the data. B) Cloud pressure (mbar). C) Visual context image with selected contour overlays to show enhanced ammonia mole fraction and lowest pressure (highest) clouds. D) Same as C), but with arrows indicating presumed upwelling (black ⊙), downwelling (white ⦻), and horizontal flow (red arrows). Figure 2. Two ammonia enhancements (4 & 3 from Figure 1), associated plumes, and NEDFs are analyzed for cloud pressure and ammonia abundance. Three observations are assessed with the targets near nadir viewing. A) Ammonia mole fraction, cloud pressure, and visual context image with overlaid rectangles indicating regions-of-interest (ROIs). B) Time series of cloud pressure (left) and ammonia mole fraction (right) over the three observations. C) Scatter plot of all ammonia and cloud measurements in each ROI (left) and of the averages over the three observations. Note that the NEB data are provided as a stable reference.ReferencesChoi, D. S. et al. 2013. Icarus, 223, 832. Hill, S. M. et al. 2024. Earth and Space Science, 11(8), e2024EA003562.Fletcher, L. N. et al. 2020. Journal of Geophysical Research (Planets), 125, e06399. Irwin, P. G. J. et al. 2025. Journal of Geophysical Research: Planets, 130(1), e2024JE008622. Showman, A. P., & Dowling, T. E. 2000. Science, 289, 1737-1740.

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...

The jet stream on the south edge of the North Temperate Belt (NTBs jet) is liable to spectacular disturbances that emerge from deep below the visible cloud-tops. Between 1970-1990, and since 2007, these have occurred in 4-5-year cycles in which whitening of the belt is followed by outbreaks of brilliant white spots (plumes) travelling at -4.8 to -5.5 deg/day in L1 (u3 = 163-173 m/s), generating dark turbulent wakes behind them and leading to revival of the belt. The white spots are considered to be convective plumes rising from the water-cloud layer below the visible clouds [e.g. refs.1&2]. The observed cloud-top peak speed of the NTBs jet varies through this upheaval cycle. Just after an outbreak it is lowest, then it accelerates over the years before the next one (although perhaps not steadily); then the plumes appear with speeds even faster than winds recorded otherwise (Figure 1).The latest outbreak in this series began on 2025 Jan.10. It was very well observed by amateur astronomers, and reveals new details of the changes of the winds before and during the upheaval. The plumes in 2025 are described in a companion abstract (session OPS8). Here we consider what the amateur observations have revealed of the overall structure of the jet during the cycle, at the deep layer from which the plumes arise, and at the cloud-top layer which we observe.System 1 longitude (L1) is used unless otherwise stated. Drift rates (DL1) are given in degrees per day; DL3 = DL1 - 7.364 deg/day. Equivalence to u3 (m/s) is shown in Fig.1.The three primary plumes:All three primary plumes first appeared at 24.0-24.6ºN, then drifted south and accelerated eastward within a few days (see companion abstract), to remain at 23.3 (±0.3)ºN with sustained speeds of DL1 = -5.0, -5.1, and -4.8 deg/day. Typical images are in Figs.2&3; tracks are in Fig.4. As usual, they all broke up within a few days when they caught up with the wake of the next plume ahead. The wake and wake-induced plumelets:As usual, a complex wake grew rapidly (~5 deg/day) following each primary plume, consisting of the following elements (Fig.3). These had a wide range of speeds, all slower than the plumes.i) Large dark patches which formed every few days, at ~23.5-24ºN, with a wave-like appearance. Their slow speeds were ill-defined but consistent with mean speeds in previous outbreaks ranging from DL1 = -0.8 to -1.6 deg/day (u3 = 108-120 m/s), supporting their wave nature. ii) White clouds on the northern and southern sides of the wake, apparently streaming behind the plumes. iii) ‘Wake-induced plumelets’: small bright, methane-bright spots arising at the following end of the growing wake, accelerating to speeds similar to the main plume but short-lived. We tracked at least five of them (Fig.4). We suggest that they are similar plumes triggered by the approach of the following end of the wake, but in this situation they are less intense and are short-lived (see companion abstract). Zonal drift profile & zonal wind profiles:The drift rates and latitudes of tracked spots are plotted as a zonal drift profile (included in Fig.5B). All the bright spots – plumes, plumelets, and smaller white spots on the N edge of the wake – fit onto a consistent curve. The northern part of this, representing the wake-induced plumelets and the first few days of the main plumes, matches the typical spacecraft-measured zonal wind profile (ZWP) in quiescent states, so it cannot determine whether the speed at deeper levels is different from that at the cloud-tops. However, the main plumes then extend the profile to faster speeds and lower latitudes. All fit a profile which peaks at 23.3ºN, DL1 = -5.1 deg/day (u3 = +166.6 m/s). As the plumes are believed to be driven from a deep layer, this may represent the ZWP down at that level. But how are the observed cloud-top winds affected by the deeper winds, either before or during the outbreak? Does the deep ZWP take over the cloud-top winds, or is it only manifested by the plumes themselves? To investigate these issues, we have established the ZWP using hi-res amateur images taken two months before the initial outbreak and several weeks after it, and we compare the results with those published for previous outbreaks (Fig.5). Previously published pre-outbreak ZWPs all had peaks at 160-163 m/s (1979-2009) or 156-159 m/s (2015-16) at 23.6-23.9ºN, with no systematic change during the year before the outbreak. Our pre-outbreak profile, in 2024 Nov., had a sharp peak at 150 m/s at 23.5ºN. This slightly slower speed could be connected to the reduced interval between outbreaks since 2012. The plume speeds in 2020 and 2025 were likewise somewhat slower than before. Otherwise, all these results are highly consistent. Our profiles in 2025 Feb. – covering the wake – are the earliest yet produced during an outbreak, and range from a narrow peak at ~141 m/s to a broad peak at ~126-136 m/s. When compared with previous ZWPs from spacecraft, these profiles confirm that there is no detectable acceleration of the cloud-top ZWP during the outbreak, apart from broadening on the flanks of the wake; instead, it quickly collapses to a slower but sometimes broader state. Then it recovers gradually over the next two years or so.These results confirm that the jet is faster at depth than at the cloud-tops, comparable to the NEBs (7ºN) jet as shown by the Galileo Probe. The plumes and plumelets erupt from the deep-level jet, but other features at cloud-tops in that latitude do not achieve this speed.The plumes in 2025 are described in a companion abstract (session OPS8). Full details of these studies are in our 2024/25 Report no.5 [ref.3]References:Sanchez-Lavega A et 24 al. (2008) Nature 451, 437-440. Sanchez-Lavega A, Rogers JH, et al.(2017). GRL 44, 4679–4686. DOI: 10.1002/2017GL073421 Rogers J et al.(2025)....