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We expand on previous observations of magnetic reconnection in Jupiter's magnetosphere by constructing a survey of ion-inertial scale plasmoids in the Jovian magnetotail. We developed an automated detection algorithm to identify reversals in the

The RBSP and the Arase satellites have different inclinations and sometimes they fly both near the equator and off the equator on the same magnetic field line, simultaneously. Such conjunction even...

Twenty high-inclination ring-grazing orbits occurred in the final period of the Cassini mission. These orbits intercepted a region of intense Z-mode and narrowband (NB) emission (Ye et al., 2010, ) along with isolated, intense upper hybrid resonance (UHR) emissions that are often associated with NB source regions. We have singled out such UHR emission seen on earlier Cassini orbits that also lie near the region crossed by the ring-grazing orbits. These previous orbits are important because Cassini electron phase-space distributions are available and dispersion analysis can be performed to better understand the free energy source and instability of the UHR emission. We present an example of UHR emission on a previous orbit that is similar to that observed during the ring-grazing orbits. Analysis of the observed plasma distribution of the previous orbit leads us to conclude that episodes of UHR emission and NB radiation observed during the ring-grazing orbits are likely due to plasma distributions containing loss cones, temperature anisotropies, and strong density gradients near the ring plane. Z-mode emissions associated with UHR and NB emission can be in Landau resonance with electrons to produce scattering or acceleration (Woodfield et al., 2018, https://doi.org/10.1038/s41467-018-07549-4).

Measurements of electrons and ions in Saturn's ionosphere down to 1,500-km altitudes as well as the ring crossing region above the ionosphere obtained by the Langmuir probe onboard the Cassini spac ...

We investigated data compression algorithms to boost science data return from high-data-volume instruments on planetary missions, particularly outer solar system missions where every bit of data represents an engineering triumph of over severe constraints on mass (limiting antenna size) and power (limiting signal strength). We developed a methodology to (1) investigate algorithms to improve compression and (2) to work with the science teams to evaluate the effects on the science. Our algorithm for compressing the Cassini Radio Plasma Wave Science (RPWS) data achieved a factor of 5 improvement in data compression (relative to what the RPWS team was using), and our algorithm for the Cassini Ultraviolet Imaging Spectrograph (UVIS) Saturn data set achieved a much higher factor (∼70). In both cases, the investigators on the science teams who evaluated our results reported that the science goals were not compromised. Our compression algorithm for Imaging Science Subsystem images achieved on average a factor of ∼1.7 improvement in lossless compression compared to the original algorithm. We also evaluated the compression effectiveness of JPL’s Fast Lossless EXtended (FLEX) hyperspectral/multispectral image compressor on Cassini’s Visible and Infrared Mapping Spectrometer data. FLEX lossless compression provides a factor of 2 improvement over the original compression. We also explore a different range of lossy compression, which can achieve an additional factor 2 to 5 depending on the fidelity required. Our findings have implications for the design of future space missions, particularly with respect to antenna size and overall size, weight, and power budgets, by demonstrating strategies to implement better data compression. In addition to improved algorithms, we show that an iterative process involving real-time science team evaluation and feedback to update the onboard compression algorithm is both essential and feasible. We make the case that a spacecraft facility compressor hosting a toolbox of compression algorithms, available to all of the science instruments and supported by a team of compression experts, convey significant benefits. Beyond the obvious benefits of increased science return and faster playback, better data compression enables design trades between antenna size and number of science instruments on the payload.

We compare ESA PROBA-V observations of electron flux at LEO with those from the NASA Van Allen Probes mostly at MEO for October 2013. Dropouts are visible at all energy during four storms from both satellites. Equatorially trapped electron fluxes are higher than at LEO by 102 ( 2.5 MeV). We observe a quite isotropic structure of the outer belt during quiet times, contrary to the inner belt, and pitch angle dependence of high energy injection. We find a very good overlap of the outer belt at MEO and LEO at ∼0.5 MeV. We use test-particle simulations of the energetic electrons trapped in the terrestrial magnetic field to study the outer radiation belt electron flux changes during geomagnetic storms. We show that the Dst (Disturbance storm time) effect during the main phase of a geomagnetic storm results in a betatron mechanism causing outward radial drift and a deceleration of the electrons. This outward drift motion is energy independent, pitch angle-dependent, and represents a significant distance (∼1 L-shell at L = 5 for moderate storms). At fixed L-shell, this causes a decay of the LEO precipitating flux (adiabatic outward motion), followed by a return to the normal state (adiabatic inward motion) during main and recovery phases. Dst effect, associated with magnetopause shadowing and radial diffusion can explain the main characteristics of outer radiation belt electron dropouts in October 2013. We also use Fokker-Planck simulations with event-driven diffusion coefficients at high temporal resolution, to distinguish instantaneous loss from the gradual scattering that depopulates the slot region and the outer belt after storms. Simulations reproduce the slot formation and the gradual loss in the outer belt. The typical energy dependence of these losses leads to the absence of scattering for relativistic and ultra-relativistic electrons in the outer belt, oppositely to dropouts.

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 42ºN - 51ºN in magnetic latitude and 5.8 – 7.8 jovian radii (1 RJ = 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, bi-directional, and, at times, exhibited sudden intensity decreases below ∼10 keV coincident with intensity enhancements up to energies of ∼1000 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/m2) 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 timeframe. 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.

We investigate the longitudinal structure of the oxygen torus in the inner magnetosphere for a specific event found on 12 September 2017, using simultaneous observations from the Van Allen Probe B and Arase satellites. It is found that Probe B observed a clear enhancement in the average plasma mass (M) up to 3–4 amu at L = 3.3–3.6 and magnetic local time (MLT) = 9.0 h. In the afternoon sector at MLT ~ 16.0 h, both Probe B and Arase found no clear enhancements in M. This result suggests that the oxygen torus does not extend over all MLT but is skewed toward the dawn. Since a similar result has been reported for another event of the oxygen torus in a previous study, a crescent-shaped torus or a pinched torus centered around dawn may be a general feature of the O+ density enhancement in the inner magnetosphere. We newly find that an electromagnetic ion cyclotron (EMIC) wave in the H+ band appeared coincidently with the oxygen torus. From the lower cutoff frequency of the EMIC wave, the ion composition of the oxygen torus is estimated to be 80.6% H+, 3.4% He+, and 16.0% O+. According to the linearized dispersion relation for EMIC waves, both He+ and O+ ions inhibit EMIC wave growth and the stabilizing effect is stronger for He+ than O+. Therefore, when the H+ fraction or M is constant, the denser O+ ions are naturally accompanied by the more tenuous He+ ions, resulting in a weaker stabilizing effect (i.e., larger growth rate). From the Probe B observations, we find that the growth rate becomes larger in the oxygen torus than in the adjacent regions in the plasma trough and the plasmasphere.

The Juno mission is providing stunning new information about Jupiter and its environment. A new magnetic field model (JRM09) with much improved accuracy near the planet provides the basis for a better understanding of Io-related decametric radio emissions (DAM) and implications for auroral processes. Here, we selected Io-related DAM events observed by the Juno Waves instrument to shed light into the beaming angle, the resonant electron energy and radio source location by forward modeling. We use the JRM09 model to better constrain the location and observability of DAM, and characterize the loss cone-driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs with calculated beaming angles ranging from 33° to 85° and resonant electron energies up to 23 times higher than previously proposed. In addition, through a quantitative analysis, we provide an explanation regarding the higher likelihood of observing groups of arcs originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator. Note: This page provides the Juno Waves data and output values of the forward modeling of the Io-related DAM emissions discussed in Martos et al. (2020), Journal ofGeophysical Research Planets. Please, read the Readme file for details about the format.&nbsp

The Juno spacecraft entered orbit at Jupiter on July 5, 2016. Since then, Juno has orbited Jupiter in high inclination orbits, crossing the ring plane near perijove. During 20 of the first 21 crossings, the Waves instrument detected signals associated with dust impacts. The impact rate profiles show peaks of order 6 s‐1 around the ring plane with half width at half maximum ~2000‐3000 km. The polarity ratio of the impact signals didn't follow the areas of the antennas exposed to dust impacts that change due to the rotation of the spacecraft, suggesting Waves detects impacts on the Juno spacecraft and not just on the Waves antennas. The impact rate profile changed during Perijove 19, when the spacecraft rotation axis was tilted to the south, increasing the area of the solar panels exposed to impacts, indicating that the detected impacts were on the spacecraft body. Grain sizes of order 1 μm are estimated, and the differential size distribution has a slope of ‐5.1 and with number densities of order 3 x 10‐6 m‐3.

International audience; Quasiperiodic emissions are magnetospheric whistler mode waves at frequencies between about 0.5 and 4 kHz which exhibit a nearly periodic time modulation of the wave intensity. We use large data sets of events observed by the Van Allen Probes in the equatorial region at larger radial distances and by the low-altitude DEMETER spacecraft. While Van Allen Probes observe the events at all local times and longitudes, DEMETER observations are limited nearly exclusively to the daytime and significantly less frequent at the longitudes of the South Atlantic Anomaly. Further, while the events observed by Van Allen Probes are smoothly distributed over seasons with only mild maxima in spring/autumn, DEMETER occurrence rate has a single pronounced minimum in July. The apparent inconsistency is explained by considering a nondipolar Earth's magnetic field and significant background wave intensities which in these cases prevent the quasiperiodic events from being identified in DEMETER data.

International audience; Jupiter's ultraviolet (UV) aurorae, the most powerful and intense in the solar system, are caused by energetic electrons precipitating from the magnetosphere into the atmosphere where they excite the molecular hydrogen. Previous studies focused on case analyses and/or greater than 30-keV energy electrons. Here for the first time we provide a comprehensive evaluation of Jovian auroral electron characteristics over the entire relevant range of energies (~100 eV to ~1 MeV). The focus is on the first eight perijoves providing a coarse but complete System III view of the northern and southern auroral regions with corresponding UV observations. The latest magnetic field model JRM09 with a current sheet model is used to map Juno's magnetic foot point onto the UV images and relate the electron measurements to the UV features. We find a recurring pattern where the 3- to 30-keV electron energy flux peaks in a region just equatorward of the main emission. The region corresponds to a minimum of the electron characteristic energy (J. Outside that region, the >100-keV electrons contribute to most (>~70-80%) of the total downward energy flux and the characteristic energy is usually around 100 keV or higher. We examine the UV brightness per incident energy flux as a function of characteristic energy and compare it to expectations from a model.

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at low Jovian altitudes on multiple occasions. The transits covered longitudinal separations of approximately 10 degrees to 120 degrees along the footprint tail. Juno's suite of magnetospheric instruments acquired detailed measurements of the Io footprint tail. Juno observed planetward electron energy fluxes of similar to 70mW/m(2) near the Io footprint and similar to 10mW/m(2) farther down the tail, along with correlated, intense electric and magnetic wave signatures, which also decreased down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any broad inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel potential. Observed waves were primarily below the proton cyclotron frequency, yet identification of a definitive wave mode is elusive. Beyond 40 degrees down the footprint tail, Juno observed depleted upward loss cones, suggesting that the broadband acceleration occurred at distances beyond Juno's transit distance of 1.3 to 1.7R(J). For all transits, Juno observed fine structure on scales of approximately tens of kilometers and confirmed independently with electron and wave measurements that a bifurcated tail can intermittently exist. Plain Language Summary The Juno spacecraft crossed regions magnetically connected to auroral structures associated with Jupiter's moon Io on multiple occasions. The transits covered longitudinal separations of approximately 10 degrees to 120 degrees along Io's auroral tail. Juno's suite of instruments acquired detailed measurements of these auroral structures. Juno directly observed the electrons that sustain these auroral features before they crash into the atmosphere and generate the brilliant aurora. The flux of these electrons decreased as Juno transited the tail farther from Io's longitude. While there are two main explanations for Io's auroral signatures, the nature of the observed electrons in this work favors one mechanism over the other. When Juno was far from Io's longitude, the observations suggest that the spacecraft was below the point at which the electrons are accelerated into the atmosphere. For all transits, Juno observed fine structure on scales of approximately tens of kilometers and confirmed that a bifurcated tail can intermittently exist.

We report on the electron, ion, and dust number densities and the electron temperatures obtained by the Radio and Plasma Wave Science instruments onboard Cassini during the Ring-Grazing orbits. The ...

During the Ring Grazing orbits near the end of Cassini mission, the spacecraft crossed the equatorial plane near the orbit of Janus/Epimetheus (similar to 2.5 Rs). This region is populated with dust particles that can be detected by the Radio and Plasma Wave Science (RPWS) instrument via an electric field antenna signal. Analysis of the voltage waveforms recorded on the RPWS antennas provides estimations of the density and size distribution of the dust particles. Measured RPWS profiles, fitted with Lorentzian functions, are shown to be mostly consistent with the Cosmic Dust Analyzer, the dedicated dust instrument on board Cassini. The thickness of the dusty ring varies between 600 and 1,000 km. The peak location shifts north and south within 100 km of the ring plane, likely a function of the precession phase of Janus orbit.

Enceladus is the main source of neutral and charged particles in the Saturnian magnetosphere. The particles originate at more than 100 active geysers forming a plume above the south pole of the moon and are continuously released into Saturn’s magnetosphere. Therefore the understanding of the interaction of those particles and the local magnetospheric environment of the moon is very important. One technique to study that interaction is to study the typical motion of charged particles in the perturbed plasma flow and the associated magnetic field lines in the vicinity of the moon especially during close flybys. The Cassini spacecraft flew by Enceladus 23 times between 2005 and 2015 at distances between 25 and 5000 km. During some of the flybys Cassini went directly through the south polar plume. Other flybys happened north of the moon or on high-latitude trajectories with respect to the moon. In this paper we present the energetic electron measurements during those flybys obtained by the Low Energy Magnetosphere Measurement System LEMMS, part of the Magnetosphere Imaging Instrument MIMI onboard Cassini (Krimigis et al., 2004). As already shown in Krupp et al. (2012) for the first 14 flybys MIMI/LEMMS typically observes dropouts in the particle intensities in the region of disturbed field lines and in the presence of the moon itself or dense material blocking the bounce and drift motions of the particles. We present in this paper a continuation of the Krupp et al. (2012) results and add a full classification for all 23 flybys using the full data set of energetic electron measurements of MIMI/LEMMS. We distinguish the observed absorption and dust signatures into four different categories: (1) full absorption signatures when all the particles within a fluxtube connecting the spacecraft with the moon are lost onto the moon during one of the particle motions; (2) partial dropouts (ramp-like feature) when not all the particles inside the fluxtube are lost; (3) short dropouts in the fluxes when particles are suddenly lost for a short period in time; and interpret those features as full or partial losses onto the moon or its environment as a result of different plasma and dust regimes in the vicinity of Enceladus. We compare the results with those of Meier et al. (2014) and Engelhardt et al. (2015); (4) In addition we also show dust-related “false electron” measurements for those flybys when Cassini directly went through the dense regions of the south polar plume. Those “dust-peaks” can be interpreted as the result of impacting dust particles inside the LEMMS aperture or nearby creating a plasma cloud.