During the 21-22 January 2005 magnetic storm, the FAST satellite observed warm (< few keV) ions in discrete energy bands on the dayside at similar to 3,000 km altitude for more than 6.5 hr. We suggest that the ionospheric energy-banded ions represent the low-altitude edge of the warm plasma cloak observed simultaneously by magnetospheric satellites. This is a clear example of the multi-species ion energy bands (10 eV to several keV) observed during strong magnetic storms by the FAST satellite, stretching from the diffuse auroral region to the plasmapause with lifetimes up to 12 hr. The close association of these energy-banded ions with magnetic storms, their broad latitudinal extent, and the presence of multiple ion species in the same energy band, rather than at the same velocity, indicate that this is a distinct phenomenon from other types of energy-banded ions. During the 21-22 January 2005 magnetic storm, the dayside ion energy band structures, centered at 10 eV (H+), 40 eV (H+ and He+), and 160 eV (H+, He+, and O+), were consistent with a "time-of-flight and velocity filter" formation process acting on a near-cusp, impulsive outflow of a <200 eV multi-species ion-source population, poleward and in the same hemisphere as FAST. Understanding the sources and dynamics of warm energy-banded ions and their linkage to the warm plasma cloak is important because during superstorms these ions are transported to L values as low as L similar to 1.2 in the dawn sector, significantly altering the energetics of the mid-latitude ionosphere.

The inward plasma transport at the Saturnian magnetosphere is examined using the flux tube interchange stability formalism developed by Southwood & Kivelson. Seven events are selected. Three cases are considered: (1) the injected flux tube and ambient plasmas are nonisotropic, (2) the injected flux tube and ambient plasmas are isotropic, and (3) the injected flux tube plasma is isotropic, but the ambient plasma is nonisotropic. Case 1 may be relevant for fresh injections, while case 3 may be relevant for old injections. For cases 1 and 2, all but one event have negative stability conditions, suggesting that the flux tube should be moving inward. For case 3, the injections located at L > 11 have negative stability conditions, while four out of five of the injections at L < 9 have positive stability conditions. The positive stability condition for small L suggests that the injection may be near its equilibrium position and possibly oscillating thereabouts-hence the outward transport if the flux tube overshot the equilibrium position. The flux tube entropy plays an important role in braking the plasma inward transport. When the stability condition is positive, it is because the entropy term, which is positive, counters and dominates the effective gravity term, which is negative for all the events. The ambient plasma and drift-out from adjacent injections can affect the stability and the inward motion of the injected flux tube. The results have implications for inward plasma transport in the Jovian magnetosphere, as well as other fast-rotating planetary magnetospheres.

We present multi‐instrument Juno observations on day‐of‐year 86, 2017 that link particles and fields in Jupiter's polar magnetosphere to transient UV emissions in Jupiter's northern auroral region known as dawn storms . Juno ranged from 42°N to 51°N in magnetic latitude and 5.8–7.8 Jovian radii (1 R J = 71,492 km) during this period. These dawn storm emissions consisted of two separate, elongated structures which extended into the nightside, rotated with the planet, had enhanced brightness (up to at least 1.4 megaRayleigh) and high color ratios. The color ratio is a proxy for the atmospheric penetration depth and therefore the energy of the electrons that produce the UV emissions. Juno observed electrons and ions on magnetic field lines mapping to these emissions. The electrons were primarily field‐aligned, bidirectional, and, at times, exhibited sudden intensity decreases below ∼10 keV coincident with intensity enhancements up to energies of ∼1,000 keV, consistent with the high color ratio observations. The more energetic electron distributions had characteristic energies of ∼160–280 keV and downward energy fluxes (∼70–135 mW m −2 ) that were a significant fraction needed to produce the UV emissions for this event. Magnetic field perturbations up to ∼0.7% of the local magnetic field showing evidence of upward and downward field‐aligned currents, whistler mode waves, and broadband kilometric radio emissions were also observed along Juno's trajectory during this time frame. These high‐latitude observations show similarities to those in the equatorial magnetosphere associated with dynamics processes such as interchange events, plasma injections, and/or tail reconnection.

This dataset consists of: get_files.sh - a bash script to download ELS data (.DAT and .LBL) files. crossing_events_urls.txt - a text file containing URLs for each of the ELS data files. get_files.sh reads this file directly. crossing_events.txt - a text file containing the list of crossing events with associated data, obtained by processing Table S1 in [1]. labels.zip - a zip file containing directory with events for each DAT file, in YAML format. plotter.py - a plotting script in Python. requirements.txt - a file indicating dependencies for the plotting script. Data This dataset spans 1259 observations from CAPS ELS, each with a .LBL file and a .DAT file. Together, these take 128 GB of space. To download these files, do: ./get_files.sh in a Bash shell/terminal. The files are stored in the 'data/' folder (created if not present) in the current directory. ELS data files are obtained from NASA's Planetary Data System at https://pds-ppi.igpp.ucla.edu/search/view/?f=yes&id=pds://PPI/CO-E_J_S_SW-CAPS-3-CALIBRATED-V1.0/DATA/CALIBRATED For help in understanding the ELS data files, see the CAPS User Guide at https://pds-ppi.igpp.ucla.edu/ditdos/download?id=pds://PPI/COCAPS_1SAT/DOCUMENT/CAPS_USER_GUIDE/CAPS_PDS_USER_GUIDE_V1_00.PDF. Labels Unzipping the labels.zip file will create a labels/ folder in the current directory, requiring 28MB of space. Within labels/: bs/ - includes bow shock crossing events. mp/ - includes magnetopause crossing events. dg/ - includes known data-gap events. See [1]. sc/ - includes unreliable data events. See [1]. valid/ - union of all files in bs/ and mp/. all/ - union of all files in bs/, mp/, dg/ and sc/. Within the labels/bs/ and labels/mp/ folders: in/ - crossing events with the transition direction as inward. out/ - crossing events with the transition direction as outward. all/ - union of all files in in/ and out/. Each label file is a YAML file containing a 'change_points' field. The entries under this field each indicate the time of a transition event. The other fields ('bimodality' and 'negative_ions') are not relevant for this dataset. Plotting the Data (and Labels) To help visualize the data and labels, we supply a plotting script plotter.py, in Python (version 2.7). First, install dependencies with: pip install -r requirements.txt and then run: ./plotter.py -h to see the available options. Example usage (after downloading data and unzipping labels): ./plotter.py data/ELS_200418018_V01.DAT -l labels/mp/all/ELS_200418018_V01.yaml --interpolated -f max_filter -fsize 100 --title "An Observation from CAPS ELS" will open up a new window with a plot of the data. To directly save to a file, use the '-o savefilename' option. For example, ./plotter.py data/ELS_200418018_V01.DAT -l labels/mp/all/ELS_200418018_V01.yaml --interpolated -f max_filter -fsize 100 --title "An Observation from CAPS ELS" -o ELS_200418018_V01.png References [1] Jackman, C. M., Thomsen, M. F., & Dougherty, M. K. (2019). Survey of Saturn's magnetopause and bow shock positions over the entire Cassini mission: Boundary statistical properties and exploration of associated upstream conditions. Journal of Geophysical Research: Space Physics, 124, 8865– 8883. https://doi.org/10.1029/2019JA026628 The original table of magnetopause and bow shock crossing events can be found at https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1029%2F2019JA026628&file=jgra55251-sup-0001-Table_SI-S01.txt Grants NASA Contract through JPL with South West Research Institute. Grant Number: 1243218 Science and Technology Facilities Council. Grant Number: ST/L004399/1 NASA. Grant Number: 1243218 Diamond Jubilee Fellowship STFC. Grant Number: ST/L004399/1

During its more than 13 years in orbit, the Cassini spacecraft detected a large number of plasma and energetic charged particle injections in Saturn's inner magnetosphere. In the corotating frame of the planet, the plasma contained within an injection moves radially inward with the component particles gaining energy. The highest energy particles in the injection experience stronger gradient‐curvature drifts in the longitudinal direction and can drift out of the main body of the injection. We have used these drift‐out effects to estimate the inflow speed of 20 injections by surveying cases from the available plasma data. We find that the average inflow speed from our sample is 15 km/s, and the values are well distributed between 0 and 50 km/s, with a few higher estimates. We have also computed the radial travel distance of interchange events and found that these are typically one to two Saturn radii. We discuss the implications of these quantifications on our understanding of transport.

The Jovian Auroral Distributions Experiment Ion sensor (JADE‐I) on Juno is a plasma instrument that measures the energy‐per‐charge (E/Q) distribution of 0.01 to 46.2 keV/q ions over a mass‐per‐charge (M/Q) range of 1– 64 amu/q. However, distinguishing O+ and S2+ from JADE‐I's measurements is a challenging task due to similarities in their M/Q (∼16 amu/q). Because of this, O+ and S2+ have not been fully resolved in the in situ measurements made by plasma instruments at Jupiter (e.g., Voyager PLS and Galileo PLS) and their relative ratios has been studied using physical chemistry models and ultraviolet remote observations. To resolve this ambiguity, a ray tracing simulation combined with carbon foil effects is developed and used to obtain instrument response functions for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+. The simulation results indicate that JADE‐I can resolve the M/Q ambiguity between O+ and S2+ due to a significant difference in their charge state modification process and a presence of a large electric potential difference (∼8 kV) between its carbon foils and MCPs. A forward model based on instrument response functions and convected kappa distributions is then used to obtain ion properties at the equatorial plasma sheet (∼36 RJ) in the predawn sector of magnetosphere. The number density ratio between O+ and S2+ for the selected plasma sheet crossings ranges from 0.2 to 0.7 (0.37 ± 0.12) and the number density ratio between total oxygen ions to total sulfur ions ranges from 0.2 to 0.6 (0.41 ± 0.09).

Jupiter's auroral X-rays have been observed for 40 years with an unknown driver producing quasiperiodic emission, concentrated into auroral hot spots. In this study we analyze an similar to 10-hr Chandra observation from 18:56 on 18 June 2017. We use a new Python pipeline to analyze the auroral morphology, perform timing analysis by incorporating Rayleigh testing, and use in situ Juno observations to infer the magnetosphere that was compressed during the Chandra interval. During this time Juno was near its apojove position of similar to 112 RJ, on the dawn flank of the magnetosphere near the nominal magnetopause position. We present new dynamical polar plots showing an extended X-ray hot spot in the northern auroral region traversing across the Jovian disk. From this morphology, we propose setting a numerical threshold of >7 photons per 5 degrees System III longitude x 5 degrees latitude to define a photon concentration of the northern hot spot region. Our timing analysis finds two significant quasiperiodic oscillations (QPOs) of similar to 37 and similar to 26 min within the extended northern hot spot. No statistically significant QPOs were found in the southern X-ray auroral emission. The Rayleigh test is combined with Monte Carlo simulation to find the statistical significance of any QPOs found. We use a flux equivalence mapping model to trace the possible origin of the QPOs, and thus the driver, to the dayside magnetopause boundary.

The Jovian Auroral Distributions Experiment aboard Juno observed accelerated proton populations connected to Io's footprint tail aurora. While accelerated electron populations have been previously linked with Io's auroral footprint tail aurora, we present new evidence for proton acceleration due to Io's Alfvénic interaction with Jupiter's magnetosphere. Separate populations were accelerated above the Io torus and at high latitudes near Jupiter. The timing suggests the acceleration is due to Alfvén waves associated with Io's Main Alfvén Wing. The inferred high‐latitude proton acceleration region spans 0.9–2.5 Jovian radii in altitude, comparable to the expected location for electron acceleration, and suggests the associated Alfvén waves are able to accelerate electrons and protons in similar locations. The proton populations magnetically connected to Io's orbit are recently perturbed, equilibrating with the nominal torus plasma population on a timescale smaller than Io's System III orbital period of ~13 h, likely due to wave‐particle interactions. The tail populations are split into a wake‐like structure with distinct inner and outer regions, where the inner region maps to an equatorial width nearly identical to the diameter of Io. The approximately symmetric surrounding outer regions are each slightly smaller than the central region and may be related to Io's atmospheric extent. The nominal, corotational torus proton population exhibits energization throughout all regions, peaking at the anti‐Jovian flank of the inner core region mapping to Io's diameter. These proton observations suggest Alfvén waves are capable of accelerating protons in multiple locations and provide further evidence that Io's Alfvénic interaction is bifurcated.

This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE-I) sensor on Juno from 10-40 R-J in the dawn to midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5-22, and the observations are separated by equatorial (vertical bar z(mag)[R-J]vertical bar <= 1.5) and off-equator (vertical bar z(mag)[R-J]vertical bar > 1.5) regions. Plasma parameters for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ are derived by forward modeling JADE-I's energy-per-charge versus time-of-flight spectra using omnidirectional averaged convected kappa distributions and modeled instrument responses. O+ and S2+ are resolved via a ray-tracing simulation based on carbon-foil-effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to similar to 20 R-J. Ion number densities decrease with radial distance, the primary species being H+, O+, and S2+. The relative contribution of H+ and S2+ increases and decreases, respectively, in the off-equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O+ to S2+ and Sigma On+ to Sigma Sn+ number density ratios are variable, the 5 R-J bin averages for O+ to S2+ ranging from similar to 0.75-1.5 (equator) and similar to 1.1-1.8 (off-equator) and Sigma On+ to Sigma Sn+ from similar to 0.6-0.9 (equator) and similar to 0.8-1.1 (off-equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 R-J and range from similar to 100 eV to 10 keV and 1 keV to a few tens of keV, respectively.

We compare electron and UV observations mapping to the same location in Jupiter's northern polar region, poleward of the main aurora, during Juno perijove 5. Simultaneous peaks in UV brightness and electron energy flux are identified when observations map to the same location at the same time. The downward energy flux during these simultaneous observations was not sufficient to generate the observed UV brightness; the upward energy flux was. We propose that the primary acceleration region is below Juno's altitude, from which the more intense upward electrons originate. For the complete interval, the UV brightness peaked at ~240 kilorayleigh (kR); the downward and upward energy fluxes peaked at 60 and 700 mW/m2, respectively. Increased downward energy fluxes are associated with increased contributions from tens of keV electrons. These observations provide evidence that bidirectional electron beams with broad energy distributions can produce tens to hundreds of kilorayleigh polar UV emissions.

The Cassini spacecraft orbited the planet Saturn from July 2004 to September 2017, and its varied orbital trajectory took it across the magnetopause and bow shock boundaries multiple times, at varying radial distances, local times, latitudes, and phases of the solar cycle. Here we present a comprehensive list of these boundary crossings, derived primarily using data from the Cassini magnetometer instrument, with cross‐validation against the electron spectrometer data where available. There are a multitude of scientific avenues for exploitation of this list. In this work, we examine the variability in boundary location and use the crossing times in concert with models of the bow shock and magnetopause to infer the upstream solar wind dynamic pressure at the times of crossings. This analysis allows us to understand the limitations of the Cassini trajectory for studying boundary physics under a range of solar wind driving conditions. In addition, rapid traversals of the magnetosheath are used to estimate the range of speeds of boundary motion.

Our understanding of Saturn's magnetosphere has been drastically changed over the last decade, since the arrival of Cassini, the first spacecraft to go into orbit around the planet. The trajectory of Cassini allowed the Saturnian magnetosphere to be studied both in the equatorial plane and at high latitudes, in a wide range of radial distances and local time sectors. This chapter reviews the current picture of Saturn's global magnetospheric configuration and describes the local fields and particle properties in key regions like the radiation belts and the inner, middle and outer magnetosphere. The moon Enceladus, deep in the magnetosphere, is the major source of neutrals and charged particles in the magnetosphere, and in this chapter we describe how the particles are generated, transported and lost within the highly dynamic magnetosphere. We also describe how both particles and fields in the Saturnian magnetosphere vary with time, both on shorter timescales and with Saturn's seasons. We highlight some of the most recent findings and discoveries, including a formerly unknown electric field oriented in the noon-midnight direction. Finally, we discuss magnetospheric measurements planned for the final sequence of the Cassini mission in 2017, called the "Grand Finale," along with a list of open questions to be solved by future missions.

Saturn's magnetosphere has been extensively studied over the past 13 years with the now retired Cassini mission. Periodic modulations in a variety of magnetospheric phenomena have been observed at periods close to those associated with the emission intensity of Saturn kilometric radiation (SKR). Resulting from Rayleigh‐Taylor like plasma instabilities, interchange is believed to be the main plasma transport process in Saturn's inner to middle magnetosphere. Here we examine the organization of equatorially observed interchange events identified based on high‐energy (3–22 keV) H+ intensifications by several longitude systems that have been derived from different types of measurements. The main question of interest here is as follows: Do interchange injections undergo periodicities similar to the Saturn kilometric radiation or other magnetospheric phenomena? We find that interchange shows enhanced occurrence rates in the northern longitude systems between 30° and 120°, particularly between 7 and 9 Saturn Radii. However, this modulation is small compared to the organization by local time. Additionally, this organization is weak and inconsistent with previous findings based on data with a limited time span.

Future remote sensing of exoplanets will be enhanced by a thorough investigation of our solar system Ice Giants (Neptune-size planets). What can the configuration of the magnetic field tell us (remotely) about the interior, and what implications does that field have for the structure of the magnetosphere; energy input into the atmosphere, and surface geophysics (for example surface weathering of satellites that might harbour sub-surface oceans). How can monitoring of auroral emission help inform future remote observations of emission from exoplanets? Our Solar System provides the only laboratory in which we can perform in-situ experiments to understand exoplanet formation, dynamos, systems and magnetospheres.

We explore the paradigm that Saturn's plasmapause marks the boundary between the magnetic flux tubes that have been circulating around the planet for some time, accumulating a dense load of Enceladus‐sourced material, and those that have recently undergone tail reconnection, shedding the bulk of the cold plasma and retaining a more tenuous, heated population. A centrifugally driven interchange instability should develop at this boundary, producing fingers of outward propagating dense plasma and of inward propagating hot, tenuous plasma. The plasmapause should thus be identifiable as a transition from mostly‐dense‐with‐some‐tenuous to mostly‐tenuous‐with‐some‐dense plasma populations. Electron densities from the Cassini Plasma Spectrometer/Electron Spectrometer (CAPS/ELS) instrument are used to identify the location of this transition for all of the low‐latitude (<5° from the magnetic equator) passes through Saturn's inner/middle magnetosphere. The boundary is typically found near and somewhat beyond L=10 (i.e., at ~10 Rs from the planet), with a local time asymmetry such that it is closer to the planet on the night side than on the day side.

An analytical method is developed by which measurements made by the Cassini spacecraft in Saturn's magnetosheath can be used to infer the upstream solar wind parameters, specifically the solar wind speed (Vsw) and the dynamic pressure (Pd). The method is validated by comparing the results with other estimates of these parameters, including the mSWiM MHD model and magnetopause and bow shock models applied to observed boundary crossings. The comparisons suggest that the new inferred Vsw are on average ~40 km/s lower than the mSWiM values, and the dynamic pressure values are slightly lower as well. We find few of the lower Pd values predicted by mSWiM, probably because Cassini would have been inside the expanded magnetosphere under such conditions. Systematic temporal variations such as interplanetary shocks do seem to be captured well, with arrival times within several days of the MHD prediction. Compared to dynamic pressures estimated from boundary crossings with well‐known magnetopause and bow shock models, the magnetosheath‐inferred dynamic pressure tends to be somewhat lower, but within the uncertainties of the analytical derivation. Comparison of the inferred dynamic pressure with observed Saturn's kilometric radiation (SKR) activity reveals several episodes of very good temporal tracking between dynamic pressure and SKR intensity, with relatively short time delays (4–5 hr), suggesting rather direct driving. Such good tracking intervals occur almost exclusively on the dawnside of the magnetosphere, where the dominant SKR source is visible. When the tracking is good, the SKR fluxes vary roughly as the square of the dynamic pressure.

Measurement of O+ in the Earth's magnetosphere is important for monitoring and understanding the initiation and evolution of geomagnetic activity. During active times, O+ can be the most abundant ion in the magnetosphere. Furthermore, because O+ and H+ damage exposed spacecraft materials through different processes, measurement and prediction of O+ and H+ fluxes is critical for understanding cumulative damage effects to these materials resulting from the ambient plasma environment of a spacecraft. We describe a simple technique for quantitative, in situ measurement of O+ and H+ fluxes using ultrathin foils. This technique is a low‐resource addition to a standard electrostatic energy‐per‐charge analyzer followed by an array of detectors. H+ and O+ abundances up to a few tens of keV can be determined by comparison of counts in detectors having no ultrathin foil at the detector aperture, in which both H+ and O+ are detected, and adjacent detectors having a foil over the aperture of the appropriate thickness to stop the transmission of O+ but through which H+ can transit. We describe three techniques for implementing this method enabling differentiation of O+ and H+ in an instrument package significantly simpler than traditional mass spectrometers.