The Juno and Cassini missions investigated Jupiter and Saturn, respectively. Juno is on-going and continues to obtain data from its polar orbit with the goal of understanding Jupiter's origin and evolution by investigating the interior, atmosphere and magnetosphere. As the largest and most massive planets in our solar system, Jupiter and Saturn offer unique insight in the history of our solar system and how planetary systems in general form and evolve. Juno has provided new observations of the global atmospheric structure and composition, storm and lightning distribution and cloud morphology and dynamics. Our view and understanding of Jupiter’s and Saturn’s auroras and magnetosphere are ever-changing as we explore these regions in situ with coordinated efforts from Earth-based observatories such as Hubble, Hisaki, Keck, etc. Constraining the present-day interior structure and dynamics of giant planets is critical to understanding the formation and evolution of planets in our Solar System and beyond. Both the Juno and Cassini have provided a wealth of new measurements, revealing key aspects of the interiors of Jupiter and Saturn for the first time. This session will bring together both observations and theoretical interpretations to improve our understanding of giant planets interiors, atmospheres and magnetospheres. We welcome submissions on wide range of topics, including: gravity science; strong differential rotation (zonal flows); properties of intrinsic (dynamo) magnetic fields; the existence and properties of the central core; bulk composition (including helium and heavy element abundance); as well as formation scenarios and evolutionary pathways. This session includes results from atmospheric and magnetospheric observations (Juno, Cassini and Earth-based) as well as theoretical modeling of atmospheric structure, composition, dynamics, planetary aurorae, magnetospheric dynamics and processes and comparative planetology.

Convener: Scott Bolton | Co-conveners: Fran Bagenal, Yamila Miguel, Kimberly Moore, Alessandro Mura
| Attendance Thu, 07 May, 08:30–12:30 (CEST)

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Chat time: Thursday, 7 May 2020, 08:30–10:15

Chairperson: Yamila Miguel
D2910 |
Peter Kollmann, Barry Mauk, George Clark, Chris Paranicas, Quentin Nenon, Yuri Shprits, Nikita Aseev, Rob W. Ebert, Thomas Kim, Elias Roussos, Dennis Haggerty, Abi M. Rymer, Angelica Sicard, and John E. P. Connerney

The ion radiation belts just above the surface of the giant planets Jupiter and Saturn have recently been observed for the first time with Juno and Cassini. The relevant physical processes differ from Earth’s inner proton belt. Jupiter’s innermost ion belt consists of protons, oxygen, and sulfur ions. A comparison of Juno particle and plasma data with numerical modeling supports that these ions are occasionally transported from the magnetosphere across the main ring of Jupiter. It has been suggested earlier that this ring is populated through the stripping of energetic neutral atoms that are produced in the magnetosphere. This process is found to be too slow to populate the belt. After radial transport, the new ions lose energy in the tenuous ring halo inward of the main ring. This gives rise to an unusual spectral shape that rises from 100keV to 1MeV. Neutralization of the ions in the ring grains acts slower and eventually removes <100keV ions until the next transport across the ring.

Saturn’s innermost belt differs from Jupiter’s and Earth’s inner belts in the sense that Saturn’s rings are too dense and extended to allow radial transport of magnetospheric ions into the innermost belt. Saturn’s ion belts are therefore thought to be exclusively populated by cosmic ray tertiary particles from the CRAND process. While the source is different, the losses are similar as at Jupiter, namely interaction with the tenuous D-ring and the planetary exosphere. This interaction shows in the proton pitch angle distribution and has been used to constrain the scale height of Saturn’s exosphere that is difficult to do otherwise.

How to cite: Kollmann, P., Mauk, B., Clark, G., Paranicas, C., Nenon, Q., Shprits, Y., Aseev, N., Ebert, R. W., Kim, T., Roussos, E., Haggerty, D., Rymer, A. M., Sicard, A., and Connerney, J. E. P.: The innermost ion radiation belts of Jupiter and Saturn, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11829, https://doi.org/10.5194/egusphere-egu2020-11829, 2020.

D2911 |
Greg Hunt, Emma Bunce, Hao Cao, Stan Cowley, Michele Dougherty, Gabrielle Provan, and David Southwood

We examine the azimuthal magnetic field signatures associated with Saturn’s northern hemisphere auroral field-aligned currents observed in the dawn sector during Cassini’s Proximal orbits (April 2017 and September 2017). We compare these currents with observations of the auroral currents from near noon taken during the F-ring orbits prior to the Proximal orbits. First, we show that the position of the main auroral upward current is displaced poleward between the two local times (LT). This is consistent with the statistical position of the ultraviolet auroral oval for the same time interval. Second, we show the overall average ionospheric meridional current profile differs significantly on the equatorward boundary of the upward current with a swept-forward configuration with respect to planetary rotation present at dawn. We separate the planetary period oscillation (PPO) currents from the PPO-independent currents and show their positional relationship is maintained as the latitude of the current shifts in LT implying an intrinsic link between the two systems. Focusing on the individual upward current sheets pass-by-pass we find that the main upward current at dawn is stronger compared to near-noon. This results in the current density been ~1.4 times higher in the dawn sector. We determine a proxy for the precipitating electron power and show that the dawn PPO-independent upward current electron power is ~1.9 times higher than at noon. These new observations of the dawn auroral region from the Proximal suggest the possibility of an additional upward current at dawn likely associated with strong flows in the outer magnetosphere. These findings provide new insights into the dawn sector of giant planet magnetospheres.

How to cite: Hunt, G., Bunce, E., Cao, H., Cowley, S., Dougherty, M., Provan, G., and Southwood, D.: Saturn’s Auroral Field-Aligned Currents: Observations from the Northern Hemisphere Dawn Sector During Cassini’s Proximal Orbits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10615, https://doi.org/10.5194/egusphere-egu2020-10615, 2020.

D2912 |
Harry Manners and Adam Masters

The magnetosphere of Jupiter is the largest planetary magnetosphere in the solar system, and plays host to internal dynamics that remain, in many ways, mysterious. Prominent among these mysteries are the ultra-low-frequency (ULF) pulses ubiquitous in this system. Pulsations in the electromagnetic emissions, magnetic field and flux of energetic particles have been observed for decades, with little to indicate the source mechanism. While ULF waves have been observed in the magnetospheres of all the magnetized planets, the magnetospheric environment at Jupiter seems particularly conducive to the emergence of ULF waves over a wide range of periods (1-100+ minutes). This is mainly due to the high variability of the system on a global scale: internal plasma sources and a powerful intrinsic magnetic field produce a highly-compressible magnetospheric cavity, which can be reduced to a size significantly smaller than its nominal expanded state by variations in the dynamic pressure of the solar wind. Compressive fronts in the solar wind, turbulent surface interactions on the magnetopause and internal plasma processes can also all lead to ULF wave activity inside the magnetosphere.

To gain the first comprehensive view of ULF waves in the Jovian system, we have performed a heritage survey of magnetic field data measured by six spacecraft that visited the magnetosphere (Galileo, Ulysses, Voyager 1 & 2 and Pioneer 10 & 11). We found several-hundred wave events consisting of wave packets parallel or transverse to the mean magnetic field, interpreted as fast-mode or Alfvénic MHD wave activity, respectively. Parallel and transverse events were often coincident in space and time, which may be evidence of global Alfvénic resonances of the magnetic field known as field-line-resonances. We found that 15-, 30- and 40-minute periods dominate the Jovian ULF wave spectrum, in agreement with the dominant “magic frequencies” often reported in existing literature.

We will discuss potential driving mechanisms as informed by the results of the heritage survey, how this in turn affects our understanding of energy transfer in the magnetosphere, and potential investigations to be made using data from the JUNO spacecraft. We will also discuss the potential for multiple resonant cavities, and how the resonance modes of the Jovian magnetosphere may differ from those of the other magnetized planets.

How to cite: Manners, H. and Masters, A.: The Pulsating Magnetosphere at Jupiter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3651, https://doi.org/10.5194/egusphere-egu2020-3651, 2020.

D2913 |
Krishan Khurana, Chris Paranicas, and George Hospodarsky

The Jovian current sheet is the main repository of Jupiter’s magnetospheric plasma. Spatial variations in its thickness and therefore its plasma content are poorly understood because thickness determination requires a knowledge of the motion of the current sheet relative to the observing spacecraft which is hard to get. Recently, we have developed a new technique that uses the timings of any three consecutive current sheet crossings to determine the instantaneous motion of Jupiter’s current sheet relative to the spacecraft. Next by using this technique and modeling the magnetic field and electron density dataset in terms of Harris current sheet type equilibria we can estimate the thickness and plasma content of the Jovian current sheet over all local times and radial distances. Our modeling of Juno and Galileo magnetic field data shows that in all local times the current sheet thickness increases with radial distance. We also find that the Jovian current sheet is highly asymmetric in local time, being at its thinnest in the dawn sector and the thickest in the dusk sector. The current sheet thickness on the dayside is comparable to that in the dusk sector. The nightside current sheet is intermediate in its thickness to the dawn and the dusk sectors.

We show that the increase in the thickness of the current sheet with radial distance can be explained in terms of the increasing temperature and therefore the plasma beta of the current sheet with radial distance. However what causes the sharp local time variations of the current sheet is not yet fully understood. We will discuss several models of plasma transport and redistribution in Jupiter’s magnetosphere that can create local time differences in the plasma content and therefore the current sheet thickness. These models have testable implications for the structure of the magnetosphere (open versus closed, convective versus diffusive transport of plasma etc.).

How to cite: Khurana, K., Paranicas, C., and Hospodarsky, G.: Factors Controlling the Thickness of the Jovian Current Sheet , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13656, https://doi.org/10.5194/egusphere-egu2020-13656, 2020.

D2914 |
Frederic Allegrini, William Kurth, Joachim Saur, Randy Gladstone, Fran Bagenal, Scott Bolton, George Clark, Jack Connerney, Rob Ebert, George Hospodarsky, Vincent Hue, Masafumi Imai, Steve Levin, Philippe Louarn, Barry Mauk, Dave McComas, Ali Sulaiman, Jamey Szalay, Philip W. Valek, and Rob J. Wilson

Jupiter’s ultraviolet (UV) aurora, the most powerful and intense in the solar system, is caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Electrons from ~50 eV to ~100 keV are characterized over the auroral regions by the Jovian Auroral Distributions Experiment (JADE) on Juno. Investigating the characteristics of electron distributions at these energies is critical for understanding the source population for the electrons that produce Jupiter’s UV aurora and the mechanisms that accelerated them to keV and MeV energies. In this study, we present a survey of electron distributions and moments derived from JADE in Jupiter’s polar magnetosphere. We quantify the electron properties (e.g. density and temperature) and explore similarities and differences in their distributions over several Juno perijove passes, focusing on regions near the main emission.

How to cite: Allegrini, F., Kurth, W., Saur, J., Gladstone, R., Bagenal, F., Bolton, S., Clark, G., Connerney, J., Ebert, R., Hospodarsky, G., Hue, V., Imai, M., Levin, S., Louarn, P., Mauk, B., McComas, D., Sulaiman, A., Szalay, J., Valek, P. W., and Wilson, R. J.: Electron density and temperature over Jupiter’s main auroral emission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5437, https://doi.org/10.5194/egusphere-egu2020-5437, 2020.

D2915 |
Stavros Kotsiaros, John E P Connerney, John L Jørgensen, and Matija Herceg

The Juno spacecraft has been in polar orbit around Jupiter since July 4, 2016 sampling Jupiter's environment from ~1.05 Jovian radii outwards, extending to the distant reaches of the Jovian magnetosphere. Juno’s polar orbit makes it possible to acquire direct observations of the Jovian magnetosphere and auroral emissions above the poles for the first time. We have quantitatively measured magnetic field-aligned (Birkeland) currents which are associated with Jupiter's auroral emissions and have modelled the morphology of the currents based on observations collected along one of Juno’s polar periJove passes. The structure of the field-aligned currents seems to be more complex than expected showing a dynamic filamentation in the azimuthal direction and strong asymmetries between the northern and southern regions. This complexity indicates a non-steady state generation of field-aligned currents possibly with non-linear processes involved. We present a way towards modeling the field-aligned currents more systematically extending the analysis with data from multiple periJove passes. We also show the development of a composite map of field-aligned current regions above the polar aurorae. This map gives us important information on the global structure of the field aligned currents and therefore on how angular momentum is transferred between Jupiter’s atmosphere and magnetosphere.

How to cite: Kotsiaros, S., Connerney, J. E. P., Jørgensen, J. L., and Herceg, M.: Global current systems in Jupiter’s polar magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17995, https://doi.org/10.5194/egusphere-egu2020-17995, 2020.

D2916 |
Jack Connerney, Ron Oliverson, Stavros Kotsiaros, Dan Gershman, Yasmina Martos, John Joergensen, Peter Joergensen, Jose Merayo, Matija Herceg, Mathias Benn, Troelz Denver, Jeremy Bloxham, Kimberly Moore, Scott Bolton, and Steven Levin

The Juno spacecraft was inserted into polar orbit about Jupiter on July 4th, 2016, performing close passes (to ~1.05 Rj radial distance at periJove) every 53 days. By the end of its prime mission, Juno will have circled the planet 34 times, uniformly sampling longitudes separated by less than 11 at the equator. The Juno magnetic field investigation is equipped with two magnetometer sensor suites, located at 10 and 12 m from the spacecraft body at the end of one of Juno’s three solar arrays. Each contains a vector fluxgate magnetometer (FGM) sensor and a pair of co-located non-magnetic star tracker camera heads that provide accurate attitude determination for the FGM sensors. A moredetailed view of Jupiter’s planetary dynamo is emerging as Juno acquires more periJove passes, providing spatial resolution beyond that already evident in the preliminary model (JRM09, a degree 10 spherical harmonic) derived from Juno’s first 9 periJoves. A complex and very non-dipolar magnetic field dominates the northern hemisphere, while a mostly dipolar magnetic field is observed south of the equator, where the enigmatic “Great Blue Spot” resides within an equatorial band of opposite polarity. The Jovian magnetodisc, formed by a washer-shaped disc of azimuthal (“ring”) currents, stretches magnetic field lines outward along the magnetic equator. With 26 equally spaced longitudes now available we can begin to address magnetodisc variability, finding a more or less stable system of azimuthal ring currents (few % variability) and a more variable (~50%) system of radial currents that supply torque to outflowing plasma. A new magnetodisc model greatly improves knowledge of the field geometry, independently verified via observations of the particle absorption signatures of Galilean satellites. A more systematic mapping of Birkeland currents above the polar aurorae also emerges from multiple passes. These and other developments will be presented with Juno now about ¾ of the way towards completion of its primary mission.

How to cite: Connerney, J., Oliverson, R., Kotsiaros, S., Gershman, D., Martos, Y., Joergensen, J., Joergensen, P., Merayo, J., Herceg, M., Benn, M., Denver, T., Bloxham, J., Moore, K., Bolton, S., and Levin, S.: Juno’s Exploration of Jupiter’s Magnetic Field and Magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10992, https://doi.org/10.5194/egusphere-egu2020-10992, 2020.

D2917 |
Kamolporn Haewsantati, Bertrand Bonfond, Suwicha Wannawichian, and George R Gladstone

The instruments on board the NASA Juno mission provides scientists with a wealth of unprecedented details about Jupiter. In particular, the Ultraviolet Spectrograph (UVS) is dedicated to the study of Jupiter’s aurora in the 60-200 nm wavelength range. The images taken by Juno-UVS reveals for the first time a complete view of Jupiter’s aurora, including the nightside part hidden from the Earth-orbiting Hubble Space Telescope (HST). This work aims to study Jupiter’s polar aurora using images obtained from the UVS instruments. Here we present the systematic analysis of one of the most spectacular features of Jupiter’s polar-most aurora, called the bright spot. The emitted power of the bright spots ranges from a few to a hundred GWs. Within a Juno perijove, the spots reappear at almost the same positions in system III. The time interval between two consecutive brightenings is a few tens of minutes, comparable to Jupiter’s X-ray pulsation. The comparison of the time interval with X-ray observation is under the investigation. Comparing the difference perijove sequences, the system III positions of bright spots in the northern hemisphere are concentrated in a region around 175 degrees of system III longitude and 65 degrees of latitude. On the other hand, the positions of bright spot aurora the southern hemisphere are scattered all around the pole. Previous studies suggested that the bright spot could correspond to noon facing magnetospheric cusp. However and surprisingly, we have discovered that the bright spots could map to any magnetic local time, putting this interpretation into question.

How to cite: Haewsantati, K., Bonfond, B., Wannawichian, S., and Gladstone, G. R.: Jupiter’s polar auroral bright spots as seen by Juno-UVS, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3622, https://doi.org/10.5194/egusphere-egu2020-3622, 2020.

D2918 |
John L. Jørgensen, Troelz Denver, Mathias Benn, Peter S. Jørgensen, Matija Herceg, Jose M. G. Merayo, and John E. P. Connerney

The Juno MAG investigation’s dedicated star tracker, the Advanced Stellar Compass (ASC), has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere subsequent to Juno’s orbit insertion on July 4, 2016. The ASC primary function is to provide an accurate inertial attitude reference, however, the most energetic particles in Jupiter’s trapped population is capable of penetrating the radiation shield of the ASC where they are registered. Such particles have energy >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements. With a sample cadence of 250ms, the ASC renders a detailed mapping of the trapped particles throughout space traversed by Juno. The particles travelling along the magnetic field lines crossing near the orbit of Io will be strongly influenced by interaction with any matter, moon, dust or plasma, which happens to be in their trajectory. The relativistic particle flux monitored, is highly relativistic, and has as such a modest retention time in any drift shell. The short lifetime of the trapped particles, and the constant scanning of field lines connecting to the Io environment enables a detailed profiling of the dust and plasma density, as well as the effect to/from Io itself. We present the measurement and their implications for the azimuthal and radial dust cloud and plasma torus.

How to cite: Jørgensen, J. L., Denver, T., Benn, M., Jørgensen, P. S., Herceg, M., Merayo, J. M. G., and Connerney, J. E. P.: A profile of the Io dust cloud and plasma torus as observed from Juno , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18093, https://doi.org/10.5194/egusphere-egu2020-18093, 2020.

D2919 |
Eli Galanti and Yohai Kaspi

The strong zonal flows observed at the cloud-level of the gas giants extend thousands of kilometers deep into the planetary interior, as indicated by the Juno and Cassini gravity measurements. However, the gravity measurements alone, which are by definition an integrative measure of mass, cannot constrain with high certainty the detailed vertical structure of the flow below the cloud-level. Here we show that taking into account the recent magnetic field measurements of Saturn and past secular variations of Jupiter's magnetic field, give an additional physical constraint on the vertical decay profile of the observed zonal flows in these planets. In Saturn, we find that the cloud-level winds extend into the planet with very little decay (barotropically) down to a depth of around 7,000 km, and then decay rapidly, so that within the next 1,000 km their value reduces to about 1% of that at the cloud-level. This optimal deep flow profile structure of Saturn matches simultaneously both the gravity field and the high-order latitudinal variations in the magnetic field discovered by the recent measurements. In the Jupiter case, using the recent findings indicating the flows in the planet semiconducting region are order centimeters per second, we show that with such a constraint, a flow structure similar to the Saturnian one is consistent with the Juno gravity measurements. Here the winds extend unaltered from the cloud-level to a depth of around 2,000 km and then decay rapidly within the next 600 km to values of around 1%. Thus, in both giant planets, we find that the observed winds  extend unaltered (baroctropically) down to the semiconducting region, and then decay abruptly. While is it plausible that the interaction with the magnetic field in the semiconducting region is responsible for winds final decay, it is yet to be understood whether another mechanism is involved in the process, especially in the initial decay form the strong 10s meter per seconds winds.

How to cite: Galanti, E. and Kaspi, Y.: Synergized magnetic and gravity measurements probe the detailed structure of the gas giants' deep atmospheres, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4037, https://doi.org/10.5194/egusphere-egu2020-4037, 2020.

D2920 |
| David Bates Medal Lecture
From storms to planetary-scale disturbances in the atmospheres of Jupiter and Saturn
Agustín Snchez-Lavega
D2921 |
Keren Duer, Eli Galanti, and Yohai Kaspi
Jupiter's North-South asymmetric gravity field, measured by the Juno spacecraft, allowed estimating the depth of the zonal jets trough the relation between the measured density anomaly and the flow. This analysis was based on a combination of all four measured odd gravity harmonics, so the direct effect of each of them on the flow profile has not been investigated. Moreover, past calculations assumed that the cloud-level zonal wind maintains its meridional structure with depth; However, the Juno microwave radiometer measurements imply that a vertically dependent meridional profile might be more suitable, due to the reasonable relation between the Nadir brightness temperature profile and the zonal wind. In this study, we analyze in detail the possible range of structures of Jupiter’s deep jet-streams, fitting each of the Juno's measured asymmetric gravity harmonics. Specifically, we examine the possible vertical structure of Jupiter’s deep jet streams, different meridional structures of the cloud-level zonal wind and depth-dependent meridional profile compatible with the Nadir temperature tendency. We find that each odd gravity harmonic constrains the flow at a different depth, with J3 being the most dominant at depths below 3000 km, where the electrical conductivity becomes significant. J5 is the most restrictive harmonic overall, and J9 does not constrain the flow at all if the other odd harmonics are within the measurement range. Deep flow profiles constructed from perturbations to the cloud-level winds allow a more extensive range of solutions, yet when the patterns differ substantially from the cloud-level observed wind profile, the ability to match the gravity data reduces significantly. Random zonal wind profiles, unconnected to the cloud-level profile allow almost no solutions for the gravity data, and only 1% of the tested wind profiles yield any solution. Overall, we find that while interior wind profiles that diverge considerably from those at the cloud-level are possible, they are statistically unlikely. Finally, we find that meridional smoothing of the wind with depth, according to the Juno MWR brightness temperature profile, still allows fitting the measured gravity signal within the uncertainty range.

How to cite: Duer, K., Galanti, E., and Kaspi, Y.: The range of flow structures fitting Jupiter's asymmetric gravity field, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4702, https://doi.org/10.5194/egusphere-egu2020-4702, 2020.

D2922 |
Rakesh Yadav, Jeremy Bloxham, and Moritz Heimpel

Decades of observations have painted a dynamic and rich picture of the atmosphere on Saturn and Jupiter. Both planets have a dominant prograde equatorial jet, and strong zonal flows that alternate in direction at higher latitudes, with Saturn also having a mysterious hexagon shape embedded in one of the polar jets. Both planets also have numerous vortices or storms of different sizes scattered on their surface. All these features are striking examples of turbulent self-organization. While observations abound, the physics behind the formation of these dynamical features is still uncertain. Two interpretations have emerged over time: In one, the surface features are shallow, extending to depths ranging from 10s to 100s of kilometers, while, in the other, they extend to 1000s of kilometers. Here we utilize the deep interpretation and investigate the properties of rotating convection in deep spherical shells. We present three cases: In the first case a giant polar cyclone, alternating zonal flows, and a high latitude eastward jet having polygonal patterns form simultaneously; The second case generates alternating zonal flows as well as numerous cyclones and anticyclones on various latitudes; And, the third case exclusively generates anticyclones with few being as large as Jupiter's great red spot. We discuss what drives these features in these turbulent simulations, and what can we learn from these cases about the interior and surface dynamics of Saturn and Jupiter. 

How to cite: Yadav, R., Bloxham, J., and Heimpel, M.: Simulating vortices and jets in deep atmospheres of gas giant planets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5948, https://doi.org/10.5194/egusphere-egu2020-5948, 2020.

D2923 |
Heidi Becker, James Alexander, Sushil Atreya, Scott Bolton, Martin Brennan, Shannon Brown, Meghan Florence, Alexandre Guillaume, Tristan Guillot, Andrew Ingersoll, Steven Levin, Jonathan Lunine, Paul Steffes, and Youry Aglyamov

The Juno Mission has recast its spacecraft engineering star camera as a visible wavelength science imager. Developed and primarily used to support onboard attitude determination, Juno’s Stellar Reference Unit (SRU) has been put to use as an in situ high energy particle detector for profiling Jupiter’s radiation belts and as a low light sensitive camera for exploring multiple phenomena and features of the Jovian system. Juno’s unprecedented polar orbit and closest approach of ~4000 km have yielded high resolution SRU imagery of Jupiter’s lightning and aurorae from as little as 50,000 km from the 1 bar level and unique Jovian dust ring and satellite images. We will present recent SRU results and discuss the implications for Jupiter’s atmosphere that stem from the SRU lightning observations.

How to cite: Becker, H., Alexander, J., Atreya, S., Bolton, S., Brennan, M., Brown, S., Florence, M., Guillaume, A., Guillot, T., Ingersoll, A., Levin, S., Lunine, J., Steffes, P., and Aglyamov, Y.: Recent results from the imagery of Juno’s Stellar Reference Unit, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9585, https://doi.org/10.5194/egusphere-egu2020-9585, 2020.

D2924 |
Mathias Benn, John L. Jørgensen, Troelz Denver, Peter S. Jørgensen, Matija Herceg, and John E. P. Connerney

As part of the Juno MAG investigation, each magnetometer features dedicated star trackers providing accurate bias free attitude information continuously throughout the mission. These optical sensors are optimized for low-light scenarios, which enables detection of stars and objects as faint as 7-8Mv. The Juno mission features a highly elliptical polar orbit with a period of ~53 days, with periapsis as close as 3.300km above the cloud tops. In combination with the 13° off pointing of the star tracker cameras from the Juno spin axis in anti-sun direction, the Jovian night side high latitude regions regularly enters the field of regard of these star trackers. This geometry facilitates imaging low light phenomenas as lightning and aurora at a large slanted angle in the upper parts of Jupiter’s atmosphere. The large slant angle enables estimation of the vertical structure, by combining the detections with accurate attitude and spacecraft position information. We present up-to-date images of detected lightning events, visible wavelength aurora and the measured vertical structure, and discuss implications of these measurements for the Jovian atmosphere at the resulting altitudes

How to cite: Benn, M., Jørgensen, J. L., Denver, T., Jørgensen, P. S., Herceg, M., and Connerney, J. E. P.: Measured Elevation of Lightning and Aurora in the Jovian Atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19958, https://doi.org/10.5194/egusphere-egu2020-19958, 2020.

D2925 |
Laura Kulowski, Hao Cao, and Jeremy Bloxham

The antisymmetric part of Jupiter's zonal flows is responsible for the large odd gravity harmonics measured by the Juno spacecraft. Here, we investigate the contributions to Jupiter's odd gravity harmonics (J3, J5, J7, J9) from dynamics in the dynamo region and the deep atmosphere. First, we estimate the odd gravity harmonics produced by zonal flows in the dynamo region. Using Ferraro's law of isorotation, we construct physically motivated profiles for dynamo region zonal flow. We use the vorticity equation to determine the density perturbations associated with the flows and then calculate the odd gravity harmonics. We find that dynamo zonal flows with root mean square (RMS) velocities of 10 cm/s would produce J3 values on the same order of magnitude as the Juno measured value, but would not significantly contribute to J5, J7, and J9. Next, we examine the gravitational contribution from zonal flows above the dynamo region. We consider a simple model where the observed surface winds are barotropic (i.e., z-invariant) until they are truncated at some depth by some dynamical process, such as stable stratification and/or MHD processes. We find that barotropic zonal flow in the strongly antisymmetric northern (13°-26°N) and southern (14°-21°S) jets extending to the likely depth of a rock cloud layer or deep radiative zone can account for a significant fraction of the observed gravity signal.

How to cite: Kulowski, L., Cao, H., and Bloxham, J.: Contributions to Jupiter's gravity field from dynamics in the dynamo region and deep atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10704, https://doi.org/10.5194/egusphere-egu2020-10704, 2020.

D2926 |
Gerald Eichstädt, Candice Hansen, and Glenn Orton

During almost every perijove pass in more than three years of Juno's ~53-day polar orbits around Jupiter, its wide-angle visible-light camera, JunoCam [1], has imaged Jupiter's south polar region [2].

We sought to determine whether these images could be used for prognostic “weather forecasts” in Jupiter. One of the simplest fluid dynamical models suitable for forecasting dynamical behavior of essentially barotropic incompressible flows of very low viscosity is the 2D Euler fluid. Vortex methods [3] are particularly suitable for modeling the resulting turbulence.

Sequences of images taken with a cadence of several minutes reveal small motions of the cloud tops within the illuminated area of the pole. The south pole itself has been visible in the twilight.

Raw JunoCam image data are transformed into an equidistant south-polar azimuthal map, roughly illumination-adjusted, high-passed with local contrast-normalization, and registered.
A streamfunction describing the velocity field approximately is derived from a sequence of consecutive maps of a common perijove flyby. Running a Monte-Carlo approach for stereo correlation repeatedly with different pseudo-random number sets returns an ensemble of streamfunctions.
The Laplacian of a streamfunction returns the vorticity values for a randomized 2D vortex particle seed as initial conditions of a grid-free vortex method. Applying the Biot-Savart law [3, p.19ff] on a 2-spherical geometry to the vorticity field returns the velocity field. A single-step explicit Runge-Kutta method of order 4 or 5 and fixed time steps advects the 4th-degree Gaussmollified vortex particles. Measuring the area of their Voronoi cells (Dirichlet/Thiessen polygons) reassesses the radius of the vortex particles. The method allows for some divergence. An approximately inviscid and incompressible 2D-flow is simulated over 2 up to 54 real-time days or about one Juno orbital period. The randomized nature of the method induces simulation ensembles for a given streamfunction by repeated runs.

Reducing the streamfunction to a Morse-Smale complex returns idealized model vortex seeds.

JunoCam images of the south polar region taken during a perijove pass provide an ensemble of dynamical data. These initial conditions extend to ensembles of forecast runs of the 2-spherical dynamics of the visible cloud tops in Jupiter's south polar region. We find that JunoCam images of
Jupiter's south polar region allow for reasonably plausible forecasts of the dynamics of the observed area with grid-free 2D vortex methods over at least a few days.

[1] C.J. Hansen, M.A. Caplinger, A. Ingersoll, M.A. Ravine, E. Jensen, S. Bolton, G. Orton.
Junocam: Juno’s Outreach Camera. Space Sci Rev 2013:475-506, 2017
[2] F.Tabataba-Vakili,J.H.Rogers,G.Eichstädt,G.S.Orton,C.J.Hansen,et al. Long-term Tracking of
Circumpolar Cyclones on Jupiter From Polar Observations with JunoCam. Icarus 335, 113405,
[3] G.-H. Cottet, P. D. Koumoutsakos, Vortex Methods: Theory and Practice, Cambridge University
Press, 2000

How to cite: Eichstädt, G., Hansen, C., and Orton, G.: Fluid Dynamical 2D Simulations of Jupiter's South Polar Region Based On JunoCam Image Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12025, https://doi.org/10.5194/egusphere-egu2020-12025, 2020.

D2927 |
Steven Levin and the Juno Microwave Radiometer Team

Juno is a spin-stabilized, solar-powered spacecraft in a highly eccentric 53.5-day polar orbit about Jupiter, with perijoves at about 5000 km above the cloud tops. From this unique vantage point, the Juno Microwave Radiometer (MWR) measures the radio emission in 6 channels, at wavelengths ranging from 1.4 to 50 cm, with 100 mS sampling throughout each spin of the spacecraft.  This data set covers the Jovian atmosphere over a wide range of latitudes, longitudes and emission angles, resulting in discoveries, puzzles, and fresh insights related to the distribution and concentration of ammonia and water, atmospheric dynamics, lightning, and other aspects of the atmosphere at depths as deep as 100 bars or more. We will present an overview of MWR results to date, incorporating data from 22 perijove passes.

How to cite: Levin, S. and the Juno Microwave Radiometer Team: Jupiter As Seen By The Juno Microwave Radiometer: A Progress Report, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12997, https://doi.org/10.5194/egusphere-egu2020-12997, 2020.

D2928 |
Yixin Sun, Ying Liu, Yixin Hao, Elias Roussos, Qiugang Zong, Xuzhi Zhou, Chongjing Yuan, and Norbert Krupp

Multi bands electron flux enhancement are found via Cassini /LEMMS PHA measurements.  The enhancement extends extremely large Lshells from L=10 to even L=5 at energy from 100 keV to 1 MeV, which is quite different from previously recognized injection events at Saturn but similar to Zebra Stripes identified at Earth.  Cases are presented by Hao et al showing the evolution of a Zebra Stripe event, and statistics here will show the spatial distribution of stripe events . The result shows that Zebra Stripe is indeed universal at Saturnian inner magnetosphere, although there exists a day-to-night asymmetry. The evolution time of stripes observed by Cassini is around 40 hours indicating the occurrence frequency  of impulsive electric field which lead to this convection process. The existence of Zebra Stripes provides an insight into the formation and dynamics of giant planets' radiation belts and magnetosphere.

How to cite: Sun, Y., Liu, Y., Hao, Y., Roussos, E., Zong, Q., Zhou, X., Yuan, C., and Krupp, N.: Statistics of Zebra stripes at Saturn magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4794, https://doi.org/10.5194/egusphere-egu2020-4794, 2020.

D2929 |
Zsofia Bebesi, Geza Erdos, Melinda Dosa, and Karoly Szego

            We present a comprehensive statistical analysis of Short Large Amplitude Magnetic Structures (SLAMS) upstream of the quasi-parallel bow shock of Saturn. During its mission Cassini extensive surveyed the quasi-parallel regime. For this study we used the measurements of the Cassini Plasma Spectrometer (CAPS) and the Magnetometer (MAG).

            The SLAM structures locally act as fast mode shock waves, and we observed possible ion beam reflection, multiple ion beams, deceleration and plasma heating of the solar wind protons. These features are in agreement with the near Earth observations. We also detected whistler precursor waves multiple times, which was also documented in studies of the Earth's foreshock region. Since the frequency of the upstream ULF waves detected at Saturn is lower than it is at Earth, it also has an effect on the spatial extension of the SLAM structures, which arise from these waves. With only one spacecraft's measurements it is not possible to study the SLAMS with the same efficiency as with the four-point measurements of the CLUSTER probes, but the basic observational features and the description of their evolutional characteristics are summarized.

How to cite: Bebesi, Z., Erdos, G., Dosa, M., and Szego, K.: Analysis of short large amplitude magnetic structures at the Kronian bow shock, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7182, https://doi.org/10.5194/egusphere-egu2020-7182, 2020.

Chat time: Thursday, 7 May 2020, 10:45–12:30

Chairperson: Alessandro Mura
D2930 |
Davide Grassi, Giuseppe Sindoni, Alberto Adriani, Alessandro Mura, Christina Plainaki, and Scott Bolton

The JIRAM instrument on board of the Juno spacecraft includes a spectrometer that operates in the range 2-5 μm with a spectral resolution of about 15 nm.
The signal measured between 2 and 3.1 um is due to the scattering of solar photons by aerosols in the daytime Jupiter atmosphere and, as such, it has been partially exploited in [1] to study the structure of "white ovals" vortexes in the southern hemisphere.
This contribution reviews the current status and issues of analysis of JIRAM data in this solar-dominated spectral range, with several examples from different latitudes. Modeling of vertical density profile of clouds is largely based on recent results of [2].
In JIRAM spectra, the region between 2.7 and 3.1 does not show any firm evidence of ammonia ice, that would be expected to produce clear spectral features here even when massively coated with contaminants such as tholines. It is therefore difficult to properly model the data assuming the optical properties of aerosols of any given realistic composition.

[1] Sindoni, G., et al. (2017) doi: 10.1002/2017GL072940
[2] Braude, A. S., et al. (2020) doi: 10.1016/j.icarus.2019.113589

How to cite: Grassi, D., Sindoni, G., Adriani, A., Mura, A., Plainaki, C., and Bolton, S.: Jupiter dayside as seen by JIRAM-Juno: current status and examples of spectral data analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7318, https://doi.org/10.5194/egusphere-egu2020-7318, 2020.

D2931 |
Joshua Dreyer, Erik Vigren, Michiko Morooka, Jan-Erik Wahlund, Stephan Buchert, and J. Hunter Waite

The present study combines RPWS/LP and INMS data from Cassini's orbit 292, which reached an altitude of 1685 km at the lowest point, to constrain the effective recombination coefficient α300 from measured densities and electron temperatures at a reference electron temperature of 300 K. Assuming photochemical equilibrium at these low altitudes and linking established methods to calculate the electron production rate and the dissociative recombination rate results in a formula to calculate an upper limit for α300. This is then compared against rate constants of individual recombination reactions as measured in the laboratory.
We derive upper limits for α300 of ∼ 2.5∗10-7cm3 s-1, which suggest that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients. An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate constants > 5∗10-7 cm3 s-1 at an electron temperature of 300 K. The results do not give constraints on the nature of the negative ions.

How to cite: Dreyer, J., Vigren, E., Morooka, M., Wahlund, J.-E., Buchert, S., and Waite, J. H.: On the effective recombination coefficient in Saturn's ionosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9813, https://doi.org/10.5194/egusphere-egu2020-9813, 2020.

D2932 |
Sascha Janser, Joachim Saur, Jamey Szalay, and George Clark

Observations by the JUNO spacecraft revealed energetic, bidirectional particle populations with broadband energy distributions in the high-latitude region of Jupiter. These measurements indicate that an acceleration mechanism of stochastic nature plays a dominant role for the generation of the intense main auroral oval. In our current work, we investigate the heating of an energetic upward proton population recently observed by JUNO in the Io flux tube wake near Jupiter. We try to infer on the relevant physical acceleration process by considering a resonant as well as a non-resonant wave-particle interaction mechanism, both based on Alfven waves. We focus on necessary temporal scales to drive these mechanisms efficiently and also on the released wave energy by means of the transported Poynting flux along the flux tube.

How to cite: Janser, S., Saur, J., Szalay, J., and Clark, G.: Wave-particle interaction in the Io flux tube, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11791, https://doi.org/10.5194/egusphere-egu2020-11791, 2020.

D2933 |
Daniel Santos-Costa, Emma Woodfield, Doug Menietti, George Hospodarsky, George Clark, Peter Kollmann, Chris Paranicas, and Wei-Ling Tseng
We present results from a three-dimensional diffusion theory model, which solves the time dependent Fokker-Planck equation with physical terms representing energizing, source and loss processes to interpret key features in the radial and angular distributions of > 1 keV-energy electrons at Saturn. Cassini observations of eV-keV electron Pitch-Angle Distributions (PADs) at Saturn have revealed a spatial structuring, with little temporal and longitudinal dependence, that can be broken up into three distinct regions [1]: (1) a region dominated by field-aligned PADs from ~12-15 Rs, (2) a transition region from ~8-12 Rs in which butterfly distributions are typically observed, and (3) a region inside ~8 Rs dominated by trapped PADs. Past studies have explained field-aligned PADs by the presence of field aligned currents and acceleration mechanisms in the auroral region [2], while pancake profiles would be the result of inward adiabatic transport [3]. It was argued that energetic electrons are adiabatically energized during inward motion and their PADs would radially evolve from field-aligned (> 15 Rs) to butterfly to pancake/isotropic inside ~8 Rs [4,5,6]. Although Cassini had unveiled Enceladus' dense and extended neutral cloud, little had been done regarding the role of neutrals on the distributions of electrons. We have subsequently combined multi-instrument data analyses of Cassini observations (particle, field and waves) and a diffusion theory model of charged particle fluxes to test the scenarios of the origins and radial evolution of electrons' PADs in the region ~2-15 Rs. In our work, Cassini CAPS/ELS, MIMI/LEMMS and MAG are used to both constrain the model at its boundary conditions and discuss our simulation results with in-situ data. Our radial transport is initially constrained by MIMI/LEMMS observations of micro-signatures [7] and assumed to be adiabatic [8]. Our simulation results show that the adiabatic transport cannot entirely explain the radial and angular features of energetic electrons within the ~2-15 Rs region. The coupling of different mechanisms is required into our model to obtain better agreements with in-situ data. The implementation of a supra-thermal electron population at high-latitudes appears to be a reasonable source of magnetospheric particles beyond ~9 Rs. While impact-ionization and Bremsstrahlung are insignificant mechanisms for > 1 keV-energy electrons, coulomb collisions with neutrals efficiently alter the electron distributions inside ~9 Rs. The drastic depletion observed in the electron fluxes inside ~9-10 Rs is partially explained by the interaction of electrons with neutrals. To pursue our understanding of radial and angular distributions of > 1 keV electrons inside ~7-8 Rs, we are currently investigating the role of dust, cold plasma and waves. Interactions with dust and plasma particles seem to have limited effects. Past studies showed that wave-particle interactions at Saturn are inconclusive [9,10]. Nonetheless, we propose to revisit the role of waves at Saturn as only the interaction with whistler mode chorus waves was examined and the role of coupled processes not discussed. We will thus present our latest results of the interactions of neutrals, dust and plasma environments, and electromagnetic waves with Saturn’s energetic electron population from a physics-based modeling approach. 
[1] Clark et al., PSS, Volume 104, 2014
[2] Saur et al, Nature, Volume 439 (7077), 2006
[3] Paranicas et al., GRL, Volume 34 (2), 2007
[4] Rymer et al., JGR, Volume 113 (A1), 2008
[5] Schippers et al., JGR, Volume 113 (A7), 2008
[6] Rymer et al, PSS, Volume 57 (14-15), 2009
[7] Roussos et al., JGR, Volume 112 (A6), 2007
[8] Kollmann et al., JGR, Volume 123, 2018
[9] Lorenzato et al., JGR, Volume 117, 2012
[10] Shprits et al., JGR, Volume 117, 2012

How to cite: Santos-Costa, D., Woodfield, E., Menietti, D., Hospodarsky, G., Clark, G., Kollmann, P., Paranicas, C., and Tseng, W.-L.: Role of coupled processes on the radial and angular distributions of > 1 keV electrons at Saturn, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12090, https://doi.org/10.5194/egusphere-egu2020-12090, 2020.

D2934 |
Marco Zannoni, Alessandro Moirano, Luis Gomez Casajus, Paolo Tortora, Daniele Durante, and Luciano Iess

The innermost galileian moon Io hosts an intense volcanic activity, which ejects about 103 kg/s of gas into Jupiter's magnetosphere. Here these neutrals are ionized by interaction with the background plasma and they are accelerated from keplerian velocity to corotation velocity thanks to Alfvén's theorem. This plasma cloud around the planet (the so-called Io Plasma Torus or IPT) slowly diffuses across Jupiter's magnetic field, but high electron densities (>1000-2000 cm-3) are found between 5-8 RJ.

Juno is travelling along highly eccentric, polar orbits around the planet and flies very close to Jupiter's surface during each perijove. Thus, the radio links used for ground communication and radio science cross the IPT both in the uplink and the downlink leg. Being a dispersive medium, the torus introduces a different path delay on the X/X and Ka/Ka links established between the Ground Station and the spacecraft. Thus, the path delay can be extracted through a linear combination of the two links, and then quantitatively analyzed and fitted to different parametric models of the IPT.

In this work we have used almost all the available Juno radio occultations of the IPT in order to improve an already existing model by introducing both longitudinal and temporal variations of the electron density. To this end, we looked for the 2D Fourier expansion in longitude and time of the parameters of this model with the goal of minimizing the residuals of the fit and pointing out periodicities in the morphology of the torus.

How to cite: Zannoni, M., Moirano, A., Gomez Casajus, L., Tortora, P., Durante, D., and Iess, L.: Modelling the electron density distribution in the Io Plasma Torus using Juno radio occultations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13221, https://doi.org/10.5194/egusphere-egu2020-13221, 2020.

D2935 |
Yixin Hao, Yixin Sun, Elias Roussos, Ying Liu, Chongjing Yuan, Norbert Krupp, and Qiugang Zong

Corotating drift resonant (CDR) electrons, of which the gradient and curvature drift could cancel the corotation around the Saturn, could get efficiently radial transported when exposed to the Saturnian global convective electric field. Such fast radial transport could lead to significant adiabatic acceleration and therefore supply for the electron radiation belt population. In this work, the nonlinear trapping nature of the corotating drift resonance is investigated. Electrons trapped inside the resonant island preform a banana-like orbit in the equatorial plane. We present an estimation of the trapping limit in L shell and energy for the resonant electrons with varying first adiabatic invariant, which could be directly compared to CASSINI observations. The estimation of the trapping period also indicates that trapped electrons takes times of more hours to close their orbit than the traveling electrons. The evolution in energy spectrogram driven by Saturn's convection and corotation has also been predicted by our test particle simulations. We suggest  that the bifurcation of the 'zebra stripes' near the corotation drift resonant energy could be a diagnostic feature of the nonlinear CDR. Observations from MIMI/LEMMS with similar zebra stripes and the bifurcation have been found as predicted, proving that the electrons in Saturn's radiation belt are being transported radially by the convection and that corotating drift resonant could be a significant candidate for the plenishing of the Saturn's electron radiation belt.   

How to cite: Hao, Y., Sun, Y., Roussos, E., Liu, Y., Yuan, C., Krupp, N., and Zong, Q.: Corotating drift resonant electrons in Saturn's radiation belt: theory and observational evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20400, https://doi.org/10.5194/egusphere-egu2020-20400, 2020.

D2936 |
Ned Staniland, Michele Dougherty, and Adam Masters

In the inner region of Saturn’s rotationally-dominated magnetosphere, the governing magnetic field contributors are the internal magnetic field and the magnetodisc current sheet. The equatorially confined plasma sourced predominantly by the moon Enceladus stretches Saturn’s magnetic field lines into the characteristic ‘magnetodisc’ geometry. The extent of this effect varies due to both external and internal dynamical processes that perturb the system.

In this study, we use the complete dataset collected by the Cassini spacecraft to determine whether the magnetosphere is compressed, stretched or near some prescribed ground state. We find that there is an underlying dawn-dusk asymmetry in the ground state of Saturn’s magnetosphere, where the field is more compressed at dusk compared to dawn. Whilst Saturn spent a significant period of the Cassini mission near its ground state, we find evidence for large-scale stresses acting on the system, including large compression events that coincide with the declining phase of the solar cycle. These results are then compared to propagated solar wind data. In addition, approximately two thirds of our dataset is well described by the internal field and current sheet models, signifying the system was in steady-state during these passes. We further discuss the drivers for the non-steady state periods at Saturn and what this implies for the global dynamics of Saturn's magnetosphere.

How to cite: Staniland, N., Dougherty, M., and Masters, A.: Finding the drivers for a non-steady state and large-scale stresses acting on the Saturnian magnetosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21724, https://doi.org/10.5194/egusphere-egu2020-21724, 2020.

D2937 |
Omakshi Agiwal, Michele Dougherty, Gregory Hunt, Hao Cao, and Hsiang-Wen Hsu

Magnetic field observations from the 22 Cassini Grand Finale orbits have shown a mean lagging azimuthal magnetic field configuration on magnetic field lines mapping from Saturn to its main rings in the equatorial plane, with some orbit to orbit variability. A prominent feature is observed in the southern hemisphere on field lines connecting to the B-ring on 70% of the orbits, which is spatially consistent with the location of in-falling dust indicated by the Cosmic Dust Analyser instrument. In our work, we examine the possible connection between the in-falling charged dust and the B-ring magnetic field feature. We also use a simple steady-state model to couple the planetary ionosphere to a weakly conducting ring ionosphere over the main rings, where the model output shows an expected leading field configuration associated with the rings. The discrepancy between the simple theoretical model and the data indicates the presence of additional processes (e.g. departure from Keplerian velocity of the charged ring particles), which will be discussed. We will further discuss the likely connection between the observed lagging field configuration in the middle magnetosphere and in the inner magnetosphere.  

How to cite: Agiwal, O., Dougherty, M., Hunt, G., Cao, H., and Hsu, H.-W.: Investigating the effects of the planetary rings on the azimuthal magnetic field at Saturn , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21953, https://doi.org/10.5194/egusphere-egu2020-21953, 2020.

D2938 |
Gabrielle Provan, Tom Bradley, Emma Bunce, Stan Cowley, Michele Dougherty, Greg Hunt, Elias Roussos, Ned Staniland, and Chihiro Tao

The presence of a substantial azimuthal current sheet in Saturn’s magnetosphere was identified in Voyager and Pioneer magnetometer data.  Data from these spacecraft showed depressions in the strength of the field below that expected for the internal field of the planet alone.  This ring current was  modelled  as a simple axisymmetric current system by Connerney et al. [1980, 1983].  In this study we utilise the Connerney ring current model to look at the size, shape, current density and total current of Saturn’s ring current as observed during the Cassini proximal orbits.  We compare the variations in these parameters with the phases of the planetary period oscillations and with the occurrence of magnetospheric storms as determined from propagated solar wind data and LEMMS electron and proton data. Overall, we find that Saturn’s ring current is a dynamical environment which varies in size and magnitude due to  both  planetary period oscillations and solar-driven storms.  

How to cite: Provan, G., Bradley, T., Bunce, E., Cowley, S., Dougherty, M., Hunt, G., Roussos, E., Staniland, N., and Tao, C.: Saturn’s ring current observed during Cassini’s Grand Finale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11306, https://doi.org/10.5194/egusphere-egu2020-11306, 2020.

D2939 |
Tomas Karlsson, Lina Hadid, Michiko Morooka, and Jan-Erik Wahlund

We present the first Cassini observations of magnetic holes on the near-Saturn solar wind and magnetosheath, based on data from the MAG magnetometer. We conclude that magnetic holes (defined as isolated decreases of at least 50% compared to the background magnetic field strength) are common in both regions. We present statistical properties of the magnetic holes, including scale size, depth of the magnetic field reduction, orientation, change in magnetic field direction over the holes, and solar cycle dependence. For magnetosheath magnetic holes, also high-time resolution density measurements from the LP Langmuir probe are available, allowing us to study the anti-correlation of density and magnetic field strength in the magnetic holes. We compare to recent results from MESSENGER observations from Mercury orbit, and finally discuss the possible importance of magnetic holes in solar wind-magnetosphere interaction at Saturn.

How to cite: Karlsson, T., Hadid, L., Morooka, M., and Wahlund, J.-E.: Cassini observations of magnetic holes in the solar wind and Saturn magnetosheath, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-100, https://doi.org/10.5194/egusphere-egu2020-100, 2019.

D2940 |
Joseph Westlake, George Clark, Dennis Haggerty, Stephen Jaskulek, Peter Kollmann, Barry Mauk, Donald Mitchell, Kenneth Nelson, Chris Paranicas, and Abigail Rymer

The Jovian polar regions produce X-rays that are characteristic of very energetic oxygen and sulfur that become highly charged on precipitating into Jupiter’s upper atmosphere.  Juno has traversed the polar regions above where these energetic ions are expected to be precipitating revealing a complex composition and energy structure. Energetic ions are likely to drive the characteristic X-rays observed at Jupiter (Haggerty et al., 2017; Houston et al., 2018; Kharchenko et al., 2006). Motivated by the science of X-ray generation, we describe here Juno JEDI measurements of ions above 1 MeV, and demonstrate the capability of measuring oxygen and sulfur ions with energies up to 100 MeV. We detail the process of retrieving ion fluxes from pulse width data on instruments like JEDI (called “puck’s”; Clark et al., 2016; Mauk et al., 2013) as well as details on retrieving very energetic particles (>20 MeV) above which the pulse width also saturates. The Juno JEDI instrument is shown to have the unplanned capability to measure heavy ions to energies as high as 100 MeV. As such, the JEDI instrument has the capability to measure those ions needed to generate polar X-rays at Jupiter. (> 10’s of MeV O and/or S). We present analysis that involves separating these very energetic ions into the group that is trapped (i.e., part of the very high latitude radiation belts) and the group that is precipitating and might be linked to observed X-rays.

How to cite: Westlake, J., Clark, G., Haggerty, D., Jaskulek, S., Kollmann, P., Mauk, B., Mitchell, D., Nelson, K., Paranicas, C., and Rymer, A.: High Energy (>10 MeV) Oxygen and Sulfur Ions Observed at Jupiter from Pulse Width Measurements of the JEDI Sensors, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18599, https://doi.org/10.5194/egusphere-egu2020-18599, 2020.

D2941 |
Matija Herceg, John L. Jørgensen, Peter S. Jørgensen, Jose M. G. Merayo, Mathias Benn, Troelz Denver, and John E. P. Connerney

The Advanced Stellar Compass (ASC), attitude reference for the MAG investigation onboard Juno, has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere since Juno’s orbit insertion. The instrument performs this function by tracking the effects of radiation with sufficient energy to transit the instrument’s radiation shielding. Particles that Juno ASC observes have energy >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements.

Completing 24 highly elliptical orbits around Jupiter, results in a fairly detailed mapping of the trapped high energy flux at up to 20 Jupiter radius distances.

Traveling at velocities close to the speed of light, electrons measured by the ASC, maintain the motion governed by the three adiabatic invariants: gyrating motion around the magnetic field line, a north-south magnetic pole particle bounce, and a charge dependent drift around the planet.

The bounce period is much smaller than the Jovian rotation period, and a large east-west drift component is caused by the magnetic field gradient. For these reasons, the drift shell description traditionally used for dipolar fields, are far from adequate to describe the behavior of energetic particles travelling close to Jupiter.

In this work, we present the distribution of the trapped high energy electrons around Jupiter. Furthermore, we have constrained the spatial extent of the stable trapped regions and are presenting the distinctive pitch angle and its correlation with ”life” of a particle. At certain distances from Jupiter, pitch angle dependency is not as important to keep the particle trapped as is the injected energy. We also develop an adiabatic map which describes the radial bands for stable trapped particles as a function of the pitch angle and energy.


How to cite: Herceg, M., Jørgensen, J. L., Jørgensen, P. S., Merayo, J. M. G., Benn, M., Denver, T., and Connerney, J. E. P.: Trapped particles around Jupiter detected by Advanced Stellar Compass, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14619, https://doi.org/10.5194/egusphere-egu2020-14619, 2020.

D2942 |
Peter S. Jørgensen, John L. Jørgensen, Jose M. G Merayo, Mathias Benn, Matija Herceg, Troelz Denver, John E. P. Connerney, and Barry Mauk

The Juno mission carries the Advanced Stellar Compass (ASC) as primary attitude reference for the MAG investigation. Since Jupiter Orbit Insertion on July 4, 2016, the ASC has continuously monitored high energy particles fluxes in Jupiter’s magnetosphere. In the attitude determination process, the energetic particles with sufficient energy to penetrate the heavily shielded focal plane CCD are detected and characterized to facilitate their removal in the stellar attitude match. Thus highly energetic particles, >15MeV for electrons, >80MeV for protons, and >~GeV for heavier elements, are detected and reported every 250ms. The ASC’s highly optimized radiation shield design enables directional sensitivity, since shielding encountered by particles entering via the optics aperture is less efficient. The directionality offers preferential detection to electrons with energies between 15 and 25MeV and protons with energies between 80 and 100MeV (i.e operates as a particle telescope), whereas particles with energies above these limits may penetrate from any direction. The Juno spacecraft, rotates at 2 RPM, thus particles with energies in the band mentioned, and velocities pointing to the lens exhibit particle flux variation with the spin phase of Juno. Every periJove, Juno traverses a section of the north and south polar caps, and now, past the midpoint of nominal mission, high energetic particles in the aurora regions have been mapped with a high degree of detail. A significant feature is that very intense beams of particles are regularly measured at field lines reaching well beyond L=50, i.e. on distant closed or open field lines. These features are rapidly varying, signifying either a very limited extent, or, high time variability. In the cases where these beams contain particles with energies in the directional sensitive range of the ASC, the source of the beam is from the aurora region, suggesting a polar cap mechanism, capable of accelerating a particle directly to 20MeV. We present examples of flux profiles on open field lines.

How to cite: Jørgensen, P. S., Jørgensen, J. L., Merayo, J. M. G., Benn, M., Herceg, M., Denver, T., Connerney, J. E. P., and Mauk, B.: Jupiter polar cap high energy particle acceleration observed from Juno, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17851, https://doi.org/10.5194/egusphere-egu2020-17851, 2020.

D2943 |
Athena Coustenis, Donald Jennings, Richard Achterberg, Panayotis Lavvas, Conor Nixon, F. Michael Flasar, and Georgios Bampasidis

Titan is one of the most promising bodies in the solar system from the astrobiological perspective in particular because of its large organic content in the atmosphere and on the surface. These chemical species evolve with time. We performed an analysis of spectra acquired by Cassini/CIRS at high resolution which cover the far-IR range from 10 to 1500 cm-1 since the beginning and until the last year of the Cassini mission in 2017 and describe the temperature and composition variations near Titan’s poles and at the equator over almost two Titan seasons ([1-3]. By applying our radiative transfer code (ARTT) to CIRS data and to the 1980 Voyager 1 flyby values inferred from the re-analysis of the Infrared Radiometer Spectrometer (IRIS) spectra, as well as to the intervening ground- and space-based observations (such as with ISO), we study the stratospheric evolution over a Titanian year (V1 encounter Ls=9° was reached in mid-2010) [1,2]. CIRS nadir and limb spectral together show variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE) and also during one Titan year.

After the 2010 equinox we have thus reported on monitoring of Titan’s stratosphere near the poles and in particular on the observed strong temperature decrease and compositional enhancement above Titan’s southern polar latitudes since 2012 and until 2014 of several trace species, such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect followed the transition of Titan’s seasons from northern winter in 2002 to northern summer in 2017, while at that latter time the southern hemisphere was entering winter.

Our data show a continued decrease of the abundances which we first reported to have started in 2015. The 2017 data we have acquired and analyzed here are important because they are the only ones recorded since 2014 close to the south pole in the far-infrared nadir mode at high resolution. A large temperature increase in the southern polar stratosphere (by 10-50 K in the 0.5 mbar-0.05 mbar pressure range) is found and a change in the temperature profile’s shape. The 2017 observations also show a related significant decrease in most of the abundances which must have started sometime between 2014 and 2017 [3]. In our work, we show that the equatorial latitudes remain rather constant throughout the Cassini mission.

We have thus shown that the south pole of Titan is now losing its strong enhancement, while the north pole also slowly continues its decrease in gaseous opacities. It would have been interesting to see when this might happen, but the Cassini mission ended in September 2017. Perhaps future ground-based measurements can pursue this investigation and monitor Titan’s atmosphere to characterize the seasonal events. We have obtained thus significant results which set constraints on GCM and photochemical models.

 [1] Coustenis et al., 2016, Icarus 270, 409-420; [2] Coustenis et al., 2018, Astroph. J., Lett., 854, no2; [3] Coustenis et al., 2019, Icarus in press, https://doi.org/10.​1016/​j.​icarus.​2019.​113413.

How to cite: Coustenis, A., Jennings, D., Achterberg, R., Lavvas, P., Nixon, C., Flasar, F. M., and Bampasidis, G.: Evolution of the atmospheric organic content on Titan with seasons, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22108, https://doi.org/10.5194/egusphere-egu2020-22108, 2020.

D2944 |
Juno’s Microwave Imaging of Jupiter’s Atmosphere at Multiple Depths
Scott Bolton, Steve Levin, Michael Janssen, Fabiano Ovafuso, Zhimeng Zhang, John Arballo, Cheng Li, Michael Wong, and Glenn Orton
D2945 |
Fluid planetary dynamics in Jupiter and Saturn
Simranjeet Singh
D2946 |
Daniele Durante, Marzia Parisi, Daniele Serra, Marco Zannoni, Virginia Notaro, Paolo Racioppa, Dustin R. Buccino, Giacomo Lari, Luis Gomez Casajus, Luciano Iess, William M. Folkner, Giacomo Tommei, Paolo Tortora, and Scott Bolton

The Juno spacecraft arrived at Jupiter’s system on July 4th, 2016 and reached the mid-point of its nominal mission in December 2018, after completing 17 perijove passes. Juno is currently orbiting Jupiter in a highly eccentric orbit, with a perijove altitude of about 4000 km that provides great sensitivity to the gravitational field of the planet. The radioscience instrumentation on board Juno enables very accurate radial velocity (Doppler) measurements, with noise as low as 10 micron/s at an integration time of 60 s. The gravity field of the planet is recovered though detailed reconstruction of Juno’s motion and observation model, performed with JPL’s and University of Pisa’s latest precise orbit determination codes, MONTE and ORBIT14 respectively.

We provide an update on Jupiter’s gravity field, its tidal response and spin axis motion over the first half of Juno’s mission. Although the Doppler data collected during the first two gravity-dedicated perijove passes have been reduced to the noise level by assuming a purely axially symmetric field for the gas giant, the current dataset, which includes ten passes, hints to a non-static and/or non-axially symmetric field, possibly related to several different mechanisms, such as normal modes, localized atmospheric or deeply-rooted dynamics.

How to cite: Durante, D., Parisi, M., Serra, D., Zannoni, M., Notaro, V., Racioppa, P., Buccino, D. R., Lari, G., Gomez Casajus, L., Iess, L., Folkner, W. M., Tommei, G., Tortora, P., and Bolton, S.: Jupiter’s gravity field updates from Juno, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18349, https://doi.org/10.5194/egusphere-egu2020-18349, 2020.

D2947 |
Alessandro Mura, Alberto Adriani, Davide Grassi, Alessandra Migliorini, Marisa Moriconi, and Francesca Altieri and the JIRAM TEAM

The Jovian InfraRed Auroral Mapper (JIRAM) on board the Juno spacecraft, is equipped with an infrared camera and a spectrometer working in the spectral range 2-5 μm. JIRAM was built to study both the infrared aurora of Jupiter and its atmosphere. The imager observations are used for studying atmospheric dynamical structures, while spectroscopic ones are used for studying atmospheric dynamical structures and for investigating the abundance of some chemical species relevant for the atmosphere’s chemistry, microphysics and dynamics, such as water, ammonia, phosphine, germane and arsine.
Since the orbit insertion, JIRAM has performed several observations of the planet from the equator to poles. Unprecedented views of the polar atmospheric structures have been acquired for the 1st time thanks to the unique orbital design of the Juno mission. Spectral measurements provided the opportunity to measure abundances of minor atmospheric species at all latitudes down to pressures of 4-5 bars.  Limb observations at the low latitudes permit to probe abundances of methane and trihydrogen cation in the stratosphere and the thermosphere of the planet. 
In the north polar region, Juno discovered, in 2016, the presence of a regular eight-cyclone structure around a single polar cyclone; in the south, one polar cyclone is encircled by five circumpolar cyclones. Now, recent observations, performed in late 2019, showed that this configuration has significantly changed: the south structure is now more similar to a hexagon, while in the north there are significant hints that the octagonal shape may have been destroyed.

How to cite: Mura, A., Adriani, A., Grassi, D., Migliorini, A., Moriconi, M., and Altieri, F. and the JIRAM TEAM: Jupiter atmosphere in the infrared, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13182, https://doi.org/10.5194/egusphere-egu2020-13182, 2020.

D2948 |
Glenn Orton, Fachreddin Tabataba-Vakili, Gerald Eichstaedt, John Rogers, Candice Hansen, Thomas Momary, Andrew Ingersoll, Shawn Brueshaber, Michael H. Wong, Amy Simon, Leigh Fletcher, Michael Ravine, Michael Caplinger, Dakota Smith, Scott Bolton, Steven Levin, James Sinclair, Chloe Thepenier, Hamish Nicholson, and Abigail Anthony

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

How to cite: Orton, G., Tabataba-Vakili, F., Eichstaedt, G., Rogers, J., Hansen, C., Momary, T., Ingersoll, A., Brueshaber, S., Wong, M. H., Simon, A., Fletcher, L., Ravine, M., Caplinger, M., Smith, D., Bolton, S., Levin, S., Sinclair, J., Thepenier, C., Nicholson, H., and Anthony, A.: Small-Scale Waves and Wave-Like Features in Jupiter’s Atmosphere Detected by JunoCam, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6197, https://doi.org/10.5194/egusphere-egu2020-6197, 2020.