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Physics Physics Space Physics

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Wednesday 14 October · still arriving

Space Physics · Cross-listed from astro-ph.EP

Revealing the Spatial Distribution of Dust and Plasma Solitary Waves in Jupiter's Innermost Magnetosphere Using Juno Waves Observations

Wenyu Zhang, Hao Cao, William S. Kurth et al. (+6 more)

Jupiter's faint ring system contains micron- and submicron-sized dust whose dynamics are influenced by the planet's rapidly rotating magnetic field. Optical observations have established the morphology of the main ring and halo, but tenuous dust close to Jupiter remains difficult to characterize. We analyze nearly a decade of in-situ Juno Waves electric-field measurements using a two-stage convolutional neural network to identify and classify dust impacts, solitary waves, and other plasma waves. These in-situ dust-impact detections reveal a radially evolving structure extending well inside the traditionally observed halo. In the innermost region, dust is concentrated in a compact, equatorially symmetric layer, indicating that the optical inner boundary does not mark the end of the dust population. Farther outward, the layer expands vertically into a broad halo before contracting toward the main ring, directly revealing the toroidal morphology of the Jovian halo. Dust number density is enhanced within the halo and near the main-ring–halo transition. The vertical distribution also develops hemispheric asymmetries that vary with radial distance, consistent with an influence of Jupiter's magnetic geometry on charged-dust dynamics. In contrast, solitary waves occur predominantly at high latitudes, and their mapped magnetic footprints show a strong spatial correspondence with Jovian auroral structures, particularly the main auroral oval. Together, these in-situ measurements extend the remote-sensing picture of Jupiter's rings and reveal previously unresolved dust and plasma structures in its innermost magnetosphere.
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All authors Wenyu Zhang, Hao Cao, William S. Kurth, Mitchell M. Shen, Darrelle Wilkinson, Donglai Ma, Martin Brennan, George Hospodarsky, Scott J. Bolton

Space Physics · Cross-listed from astro-ph.SR

Flares and flux ropes: an entangled story

Rony Keppens, Yang Guo and Wenzhi Ruan

Solar flares serve as standard candles for all magnetic-reconnection-based energy releases, and their consequences into the heliosphere can be modeled from first principles. This review presents the latest developments in modeling solar flares and their associated flux rope expulsions with state-of-the-art multidimensional magnetohydrodynamic (MHD) descriptions. Observationally established ingredients beyond a single-fluid, thermal plasma evolution have been incorporated to varying degrees, and we highlight self-consistent efforts realized in "standard flare" setups.
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Space Physics · Cross-listed from astro-ph.SR

Tracking a solar energetic eruption and associated energetic particles from Sun to spacecraft

D. E. Morosan, M. Baumgartner-Steinleitner, K. Bhandari et al. (+17 more)

Context. Solar energetic particles (SEPs) in the heliosphere are produced by flaring processes on the Sun or shocks driven by coronal mass ejections (CMEs). Electrons, in particular, are regularly detected remotely as electromagnetic radiation (X-rays or radio emission), which they generate through various processes, as well as in situ by spacecraft monitoring the Sun and the heliosphere. Aims. We aim to combine remote-sensing and in situ observations of an energetic solar eruption to link energetic processes in the solar corona to energetic particles observed in situ in the heliosphere. This will be done using the tools developed in the Horizon Europe SOLER project. Methods. Here, we investigate a solar energetic eruption at the Sun together with its associated signatures of accelerated electrons observed at radio and X-ray wavelengths and combine these remote observations to in situ particles observed by spacecraft on 10 March 2024. These observations are combined with a magneto-hydrodynamic (MHD) model of the solar corona in order to make the remote to in situ connections. Results. We observe a high-energy SEP event at multiple spacecraft (>25 MeV protons and 1 MeV electrons), despite the event being associated with a slow white-light CME. Remote observations of the Sun show that the event was associated with a fast large scale coronal wave (1400 km/s) and also multiple regions where electrons are accelerated around this large scale wave observed as type II radio bursts. In addition, we observe a strong coronal dimming away from the main flaring region, providing evidence of field lines getting opened to interplanetary space, dislocated from the flare site.
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All authors D. E. Morosan, M. Baumgartner-Steinleitner, K. Bhandari, N. Dresing, G. Farwa, J. A. J. Mitchell, C. Palmroos, A. Razquin, J. Zhang, C. Briand, K. Dissauer, A. Fedeli, J. Gieseler, E. K. J. Kilpua, S. Normo, J. Pomoell, D. J. Price, A. M. Veronig, A. Warmuth, R. Vainio

Space Physics · Cross-listed from astro-ph.SR

Stationary Resistive MHD Solutions Near an Isolated Three-Dimensional Magnetic Null

Kuljeet Singh Saddal, Dieter H. Nickeler, Rodrigo Meneses Pacheco et al. (+1 more)

Magnetic null points define the magnetic field topology in stellar coronae, planetary magnetospheres, and astrospheres, and are commonly associated with magnetic reconnection. We investigate the local structure of stationary three-dimensional (3D) resistive, incompressible magnetohydrodynamic (MHD) flows in the vicinity of an isolated magnetic null and an isolated velocity stagnation point, assuming that the two nulls are colocated. The governing MHD equations are solved self-consistently using a first-order local expansion of the magnetic and velocity fields about the null. For any given magnetic-null configuration, the equations admit a two-parameter family of stationary solutions, comprising multiple solution branches with distinct velocity topologies. Along these families, the velocity-null polarity can change at bifurcation points where the flow becomes effectively 2.5D. A single magnetic null can therefore support positive-radial, negative-radial, and spiral stagnation flows, with qualitatively different inflow, outflow, and rotational properties. The associated pressure and resistivity distributions are likewise determined self-consistently and vary across the solution family, demonstrating that they are coupled to the flow topology rather than prescribed independently. The generic solutions do not require the velocity and magnetic separatrices to coincide, allowing plasma to cross the magnetic fan separatrix and providing a local reconnective flow. These results demonstrate that, in the presence of nonuniform resistivity, the magnetic topology alone does not uniquely determine the associated stationary flow, pressure, or resistivity structure around a 3D magnetic null, revealing the nonlinear feedback between all macroscopic variables and resistivity. The constant-resistivity field-aligned and spiral field-crossing solutions identified previously are recovered as special cases.
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All authors Kuljeet Singh Saddal, Dieter H. Nickeler, Rodrigo Meneses Pacheco, Michaela Kraus

Space Physics

The Gannon Storm: Citizen science observations during the geomagnetic superstorm of 10 May 2024

Maxime Grandin, Emma Bruus, Vincent E. Ledvina et al. (+12 more)

The 10 May 2024 geomagnetic storm, referred to as the Gannon Storm in this paper, was one of the most extreme to have occurred in over 20 years. In the era of smartphones and social media, millions of people from all around the world were alerted to the possibility of exceptional auroral displays. Hence, many people not only witnessed but also photographed the aurora during this event. These citizen science observations, although not from scientific instruments operated by observatories or research groups, can prove invaluable in obtaining data to characterise this extraordinary event. In particular, many observers saw and photographed the aurora at mid-latitudes, where ground-based instruments targeting auroral studies are sparse or absent. We created an online survey and circulated it within networks of aurora photographers to collect observations of the aurora and disruptions in technological systems that were experienced during this superstorm. We obtained 696 citizen science reports from over 30 countries, containing information such as the time and location of aurora sightings, observed colours and auroral forms during the geomagnetic storm. We supplemented the obtained dataset with 186 auroral observations logged in the Skywarden catalogue by citizen scientists. The main findings enabled by the data collected through these reports are that the aurora was widely seen from locations at geomagnetic latitudes ranging between 30{\deg} and 60{\deg}, with a few reports from even lower latitudes. This was significantly further equatorward than predicted by auroral oval models. The reported auroral emission colours, predominantly red and pink and intense enough to reach naked-eye visibility, suggest that the auroral electron precipitation contained large fluxes of low-energy (< 1 keV) particles. (...)
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All authors Maxime Grandin, Emma Bruus, Vincent E. Ledvina, Noora Partamies, Mathieu Barthelemy, Carlos Martinis, Rowan Dayton-Oxland, Bea Gallardo-Lacourt, Yukitoshi Nishimura, Katie Herlingshaw, Neethal Thomas, Eero Karvinen, Donna Lach, Marjan Spijkers, Calle Bergstrand

Space Physics · Cross-listed from astro-ph.SR

Magnetic Reconnection Governs the Entire Lifecycle of Solar Eruptive Magnetic Flux Rope

Xinkai Bian, Chaowei Jiang, Qingjun Liu et al. (+3 more)

While magnetic flux ropes (MFRs) are widely accepted to exist prior to many solar eruptions, the physical mechanism responsible for triggering and subsequently driving their eruptions remains debated. Classical models commonly attribute eruption onset to ideal magnetohydrodynamic instabilities, particularly the torus instability, while magnetic reconnection is often regarded as a secondary process. Using high-resolution three-dimensional MHD simulations, we investigate the eruption of an MFR that forms self-consistently through flux cancellation driven by converging motions and photospheric diffusion following an initial shearing phase. The pre-eruption MFR rises quasi-statically and reaches a height where the decay index exceeds the classical torus instability threshold, yet the system continues to evolve quasi-statically without eruption. Instead, eruption begins only when the current sheet beneath the MFR becomes sufficiently thin for magnetic reconnection to set in. Increasing numerical resolution systematically delays the eruption onset, whereas the decay index at eruption onset remains nearly unchanged, demonstrating that the onset is governed by reconnection rather than torus instability. During the eruption, magnetic reconnection continuously converts surrounding sheared arcades into newly reconnected twisted flux that merges with the pre-eruption MFR and continuously to build the erupting MFR. A component-resolved analysis of the Lorentz force work further shows that the newly reconnection flux contributes predominantly to the main acceleration phase. These results demonstrate that magnetic reconnection plays a central role throughout the entire lifecycle of the eruptive MFR: it builds the MFR, directly triggers its eruption, and provides the dominant driving of the eruption.
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All authors Xinkai Bian, Chaowei Jiang, Qingjun Liu, Xueshang Feng, Pingbing Zuo, Yi Wang

Tuesday 13 October · still arriving

Space Physics · Cross-listed from physics.ins-det

The Energetic Particle Detector Instrument on ELFIN

Colin Wilkins, Ryan Caron, Ethan Tsai et al. (+24 more)

We present the design methodology, implementation, and data products of the Energetic Particle Detector (EPD) instrument on-board the Electron Losses and Fields Investigation (ELFIN) dual SmallSat mission. ELFIN was designed to study the time-evolution of energetic particle distributions in Earth's magnetosphere, having operated in polar Low Earth Orbit (LEO) from 2018 to 2022. Each satellite's instrument payload contained a pair of detector heads to sense differential-directional fluxes of 50 keV to $\sim$5 MeV electrons (EPDE), and 50 keV to $\sim$2 MeV atomic ions (EPDI), with an energy resolution better than 50% ($\Delta E/E<0.5$). The satellites were spinning with a nominal period of 2.8 s in a plane containing Earth's background magnetic field, with particle counting intervals subdivided into 16 consecutive spin sectors. Each EPD was paired with a three-axis Fluxgate Magnetometer (FGM) sampled at 80 Hz for local pitch-angle determination. Each detector head operated on the principle of pulse-height analysis (PHA) in solid state media, collimated by a rectangular 22.5$^\circ$ field of view and entrance aperture. The EPDE contained a stack of 6 silicon detectors (0.7 cm total thickness) with 0.15 cm$^2$ str geometric factor, with ion contamination mitigated by an aperture foil and digital coincidence logic. The EPDI contained a stack of 2 silicon detectors (0.1 cm total thickness) with 0.03 cm$^2$ str geometric factor, with electron contamination mitigated by a magnetic broom stage and digital anti-coincidence logic. The total assembled mass, volume, and power required for the EPD detector heads and circuit boards were 939 g, 10$\times$9.8$\times$8.4 cm$^3$, and 2.3 W, respectively. We describe each EPD design element alongside instrument data products and processing.
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All authors Colin Wilkins, Ryan Caron, Ethan Tsai, Chris Shaffer, Patrick Cruce, Maxwell Chung, Andrei Runov, Jiang Liu, Drew Turner, Yuri Shprits, Wen Li, Michael Lawson, Emmanuel Masongsong, Cindy Russell, Eric Grimes, Jiashu Wu, Matthew Allen, Jessica Artinger, Alex Flemming, Brayden Hesford, Laura Iglesias, James King, Austin Norris, Carter Pedersen, Daniel Thomlinson, Wynne Turner, Vassilis Angelopoulos

Space Physics · Cross-listed from astro-ph.EP

Radiation limits on amino acid preservation and chiral measurement at Oxia Planum

Dimitra Atri

Amino acid enantiomeric excess (EE) is a potential biosignature, but its measurement requires sufficient surviving material as well as preserved chirality. We derive a criterion that separates abundance-limited from racemization-limited preservation and apply it to the Mars Organic Molecule Analyzer (MOMA) on the ExoMars Rosalind Franklin rover. The model combines cosmic-ray and radiogenic doses with laboratory destruction kinetics and assumed ratios of interconversion to destruction rates. For an initially homochiral population of 1000~ppmw, the surviving EE is 58% or 25% when the total abundance reaches 1~ppmw for rate ratios of 0.04 or 0.10, respectively. This abundance criterion does not ensure that both enantiomers can be quantified. Applying provisional estimates of 1~ppmw per enantiomer and 10% EE, serine at 2~m requires initial concentrations of 340 and 960~ppmw after cosmic-ray exposures of $10^{7}$ and $10^{8}$~yr, respectively, under transferred fused-silica–perchlorate kinetics and a 1.57-MGy radiogenic dose. These concentrations exceed measured meteoritic serine abundances, but do not predict the initial Oxia inventory. For organics retained in a closed host since deposition 3.9~Ga ago, the modeled radiogenic dose is 1.6–5.6~MGy across the adopted compositions. In the lower-dose case, drilling to 2~m reduces the total dose by only a factor of 1.5 after $10^{7}$~yr. The boundaries depend on mineral kinetics and organic residence time; they distinguish preserved chirality from a measurable excess.
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Space Physics · Cross-listed from physics.plasm-ph

Effects of Coulomb Collisions on the Structures of Fast Magnetosonic Shocks

Michael B. Farnell III, Fan Guo, Yi-Hsin Liu et al. (+1 more)

We present fully kinetic particle-in-cell simulations to demonstrate qualitative effects of binary Coulomb collisions on fast magnetosonic shocks. We find that with sufficiently high collisional frequencies, shock rippling and reformation can be inhibited, leading to stationary, laminar shock fronts. We observe that ion-ion collisions disrupt the motion of particles reflected back upstream that is the key for cyclical reformation. Meanwhile, the electron-ion collisions provide a Spitzer resistivity that can dissipate energy from the instability that causes shock rippling. This result helps us understand the role of collisions in laboratory shocks and possibly the outer heliosphere.
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All authors Michael B. Farnell III, Fan Guo, Yi-Hsin Liu, Xiaocan Li

Saturday 10 October

Space Physics

Validation of Space Weather Forecasting at Leonid Space

Scott Shambaugh

We validate Leonid Space's space weather forecasts through comprehensive cross-validation of retroforecasts scored against the entire F10.7 and Ap historical record. We built a unified forecast model that jointly forecasts F10.7 and Ap on all timescales from 3 hours up to multi-decade chains of future solar cycles. This was used to generate an archive of historical 15-year retroforecasts, after performing a leave-one-out fit of the model on held-out data and conditioning only on historical data available at the time. The accuracy of this archive was scored against measured space weather indices at all lookahead horizons from 1 day to 15 years, using the continuous ranked probability score (CRPS) as the primary quality metric. All other publicly available F10.7 and Ap forecast archives were scored using the same approach, including NASA's MSAFE and Schatten forecasts, SWPC's 27-day, 45-day, and Solar Cycle predictions, SWPC/USAF's RSGA, SIDC's Ursigram, CLS, Athens, KSO, BGS, SEPC's 3-day and 27-day forecasts, AFRL/NSO's SIFT, and BoM. Taken together, these 15 flux forecasts and 12 Ap forecasts compared on common lookahead metrics make up the most comprehensive cross-comparison of space weather forecasts we are aware of. Over a common forecast interval since 2000, Leonid had the lowest CRPS prediction error of any F10.7 or Ap prediction model: strictly lowest for Ap at all lookaheads and for F10.7 up to 5 years, and parity with MSAFE after 5 years. Much of this performance comes from our well-calibrated uncertainty bands, and we urge space weather forecasters to include calibrated uncertainties with their predictions and to issue retroforecast archives that can be used to rigorously evaluate their generating models.
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Friday 9 October

Space Physics · Cross-listed from astro-ph.SR

Magnetic connectivity from the Sun to the Earth with MHD models II. Impact of input magnetic maps

Barbara Perri, Silke Kennis, Brigitte Schmieder et al. (+1 more)

Connectivity estimation needs to be fast and thus usually relies on semi-empirical models. We previously established that optimised magnetohydrodynamics (MHD) models can also be used to derive magnetic connectivity, yielding good results, especially for complex configurations. However, the modelling is not the only factor that can impact the connectivity estimation. Models' results, both semi-empirical and MHD, depend heavily on the input data used to drive the simulation. In order to quantify this impact on our connectivity estimation, we used 20 different maps by four providers. We selected the period of July 2019, which corresponds to Carrington rotation (CR) number 2219, because it had already been studied in a previous paper. It corresponds to a period of minimum activity, meaning minimal interference from transient structures, but with a high-speed stream and several polarity switches. We have compared our results with in situ data from ACE and developed several visualisation techniques to validate connectivity not only for a specific date but also for a full CR. The choice of the input magnetic map drastically affects the connectivity estimates, with global scores going from 28% global agreement to 63% in the most extreme case. The HMI and GONG maps consistently gave the best connectivity estimations, with more than 50% correct results of the full CR. For this specific period, the GONG-ADAPT maps yielded the least reliable results, with a score below 35%. This is not surprising, as we have shown before that COCONUT required parameter adjustments for these maps. However, WSO maps which showed poor coronal agreement actually provided good connectivity estimates, showing that the Heliospheric Current Sheet (HCS) location is in the end the most crucial parameter for connectivity. Consistent data over a full Carrington rotation are to be favored compared to daily.
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All authors Barbara Perri, Silke Kennis, Brigitte Schmieder, Stefaan Poedts

Space Physics · Cross-listed from astro-ph.IM

First Experimental Results of Space Object Detection Using the InteRFeX Array

Bhaskar Ahuja, Thomas Crowther, Steven Tingay et al. (+3 more)

This paper presents the first experimental validation of InteRFeX, a non-uniform receive only (passive) array located at the Nova Systems Space Precinct in Peterborough, Australia, designed for space domain awareness applications. It operates over a frequency range of 70 to 300 MHz and is capable of functioning in a range of observational modes, including as a coherent passive bistatic radar for space surveillance, which is the focus of this work. InteRFeX exploits commercial broadcast transmissions as illuminators of opportunity, combining cross-ambiguity function processing for bistatic range and range-rate retrieval with MUSIC-based direction-of-arrival (DoA) estimation for angular localization. The International Space Station (ISS) serves as the experimental target, with measurements evaluated against Two-Line Element (TLE) orbit predictions. Taking advantage of the dual-polarized array, all four reference–surveillance polarization combinations are evaluated, revealing differences in detection rate and mean signal-to-noise ratio (SNR) over the observation pass, with bistatic-range RMSEs of approximately 1 km relative to the TLE-derived reference. Independently, the MUSIC-based DoA estimates exhibit a mean angular separation of approximately $0.45^\circ$ from the TLE-derived reference directions. The angular deviations are further decomposed into along-track and cross-track components, enabling a more detailed characterization of the DoA offsets relative to the TLE-derived reference trajectory. The processing framework also includes a first-order bistatic link-budget analysis to estimate the expected SNR over the observation geometry. These results demonstrate the feasibility of passive-radar space domain awareness using radio-interferometric array technology and establish the proposed signal-processing pipeline as a basis for a dedicated coherent passive-radar mode within InteRFeX.
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All authors Bhaskar Ahuja, Thomas Crowther, Steven Tingay, Andrew Guidi, Luca Gentile, Marco Martorella

Thursday 8 October

Space Physics · Cross-listed from physics.plasm-ph

Kinetic wave activity and proton heating in 3D hybrid simulations of decaying balanced and imbalanced Alfvénic turbulence

C.A. González, T.A. Bowen, A. Mallet et al. (+1 more)

We investigate turbulent dynamics from large to sub-proton scales, the kinetic wave activity and resulting proton heating in three-dimensional hybrid-kinetic simulations of freely decaying balanced and imbalanced Alfvénic turbulence. We considered initial fluctuations with same amplitude and spectral shape but different degrees of correlation between velocity and magnetic field perturbations (i.e., normalized cross-helicity), which define the corresponding turbulent regimes. We found that our balanced turbulence simulation exhibits stronger energy dissipation and more efficient proton heating compared to the imbalanced case. On the large fluid scales, the two simulations undergo distinct nonlinear dynamic and energy cascades, leading to different spectral properties once turbulence is well developed. At sub-proton scales, fluctuations are predominantly oblique with right-hand polarization, a property common to both regimes. In contrast, only the imbalanced simulation displays substantial wave power parallel to the guide magnetic field, with clear signatures of ion-cyclotron waves. These waves are excited in regions with strong temperature anisotropy that arise during the initial nonlinear steepening of Alfvénic fluctuations, a process that simultaneously generates parallel-propagating proton beams. Furthermore, non-Maxwellian features emerge in velocity space, indicating different heating mechanisms in balanced and imbalanced regimes and providing evidence for the role of kinetic instabilities in regulating the turbulent dynamics. Overall, these results show that cross-helicity is a key parameter controlling the large-scale evolution, kinetic activity, and energy dissipation in collisionless turbulent plasmas.
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All authors C.A. González, T.A. Bowen, A. Mallet, A. Tenerani

Wednesday 7 October

Space Physics · Cross-listed from astro-ph.SR

Wave-Growth-Limited Particle Confinement in a Near-Parallel Interplanetary Shock Observed by Parker Solar Probe

A. Kouloumvakos, I. C. Jebaraj, M. A. Malkov et al. (+11 more)

Collisionless shocks confine the particles they accelerate with the upstream wave field they themselves drive. Streaming particles resonantly amplify Alfvén waves, and the waves then confine the same particles by pitch-angle scattering. The rigidity a shock precursor can hold is therefore capped by how fast those waves grow, and that coupling has not previously been constrained in-situ at any interplanetary shock. Here we report Parker Solar Probe measurements of a fast, near-parallel coronal mass ejection-driven shock at 0.24~AU on 2023 March 13 that constrain this wave-particle coupling through the energetic-particle population it accelerates. We measure the spectral folding energy, the boundary between the confined and the upstream-escaping protons, and find that it falls from $\sim$6 to $\sim$1.5~MeV as $E_\mathrm{fold}\propto\Delta t^{\,\alpha}$ with $\alpha\simeq0.34$, where $\Delta t$ is the time remaining before shock arrival. One precursor convective time before arrival this boundary is at $E_\mathrm{c}\simeq 2.46$~MeV, a characteristic confinement energy of a precursor of scale $L_\mathrm{EP}$. Read through the quasi-linear marginal-stability condition, the same evolution implies a resonant wave-growth timescale $\tau_\mathrm{growth}(E)\propto E^{1/\alpha}\simeq E^{2.92}$ that exceeds the precursor convective time above $E_\mathrm{c}$. The post-shock pitch-angle anisotropy reverses sign across the same confinement–escape transition at 2–5~MeV. The rigidity to which a shock precursor can confine particles is therefore set, in-situ, by how quickly the streaming population builds its own confining waves.
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All authors A. Kouloumvakos, I. C. Jebaraj, M. A. Malkov, G. D. Berland, M. Gedalin, N. Wijsen, C. M. S. Cohen, O. V. Agapitov, D. J. McComas, D. G. Mitchell, E. Husidic, S. Yadav, M. E. Hill, R. McNutt

Space Physics · Cross-listed from astro-ph.SR

The existence of null points of flow and magnetic fields as prerequisites for the presence of astropauses and their co-location

Dieter H. Nickeler, Kuljeet S. Saddal, Rodrigo Meneses Pacheco et al. (+1 more)

Astropauses can be defined via magnetic or fluid separatrices. For the boundary layer between the stellar wind and the local interstellar medium, two separatrices can occur, the magnetopause and the hydropause. The question is whether they are identical. To address this, we investigate under which conditions the null points of the magnetic and velocity field, which define the corresponding separatrices, coincide spatially. We analysed the case of a non-monotonous pressure distribution driving stationary counterstreaming ideal HD flows and demonstrate that the existence of an extremum of the pressure in the 3D case together with a non-degeneracy condition on the velocity field implies that this point is also a stagnation point. Turning to ideal MHD and considering the regularity of all fields, we formulated the momentum equations, revealing their quasi-linearity. This allowed us to prove the occurrence of null points by examining the rank of the Jacobians of the vector fields. We found that for a given null point of either the velocity or the magnetic field at the pressure extremum, the pendant vector field has a co-located null if the Jacobian of this field is non-singular. We extended the analysis to resistive MHD and further to MHD with general non-ideal terms and proved that if at least one of the first-order momentum equations is ideal, the stagnation point and the magnetic null point are co-located. Even for general fluid theory, the two null points co-locate as long as the curl of the generalised non-ideal terms is zero at one of them or can be represented by a linear operator in the magnetic and velocity field. In general, it is not excluded that the velocity and magnetic nulls are dislocated. However, this would require specific properties of the curl of the non-ideal term, which would reduce the probability of a relaxed quasi-stationary configuration.
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All authors Dieter H. Nickeler, Kuljeet S. Saddal, Rodrigo Meneses Pacheco, Michaela Kraus

Tuesday 6 October

Space Physics · Cross-listed from astro-ph.SR

Does Diffusive Shock Acceleration Reach Steady State? Insights from a Near-Sun Shock Observed by Parker Solar Probe

Immanuel Christopher Jebaraj, Mikhail Malkov, Nicolas Wijsen et al. (+7 more)

Collisionless shocks accelerate particles at a rate set by the diffusion coefficient of those particles in waves they themselves generate. Theory fixes that coefficient only in steady state, and no measurement has tested whether an evolving shock ever reaches that state. We report Parker Solar Probe observations of a fast, near-parallel interplanetary shock at 0.24 au, encountered four hours after eruption, with the upstream waves and the protons they scatter recorded on the same magnetic field line. From the wave spectra alone we derive the parallel mean free path of 0.05-30 MeV protons, resolved in energy and in distance from the shock. The mirror force of the measured compressive fluctuations supplies the scattering through the pitch angles that gyroresonance cannot reach. The mean free path grows with distance nearly as the steady self-generated solution requires, yet the steady balance holds at one energy only, near 1.3 MeV. The intensity profiles are a factor of two shallower than the measured coefficient predicts, because the waves are still growing. Confinement fails between 2.3 and 6 MeV, beginning a factor of two below what the age of the shock allows. The growth of the waves its own particles drive, rather than its age or its size, limits the energy an evolving shock confines.
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All authors Immanuel Christopher Jebaraj, Mikhail Malkov, Nicolas Wijsen, Oleksiy Agapitov, Athanasios Kouloumvakos, Alexandr Afanasiev, Federico Fraschetti, Edin Husidic, Christina Cohen, Rami Vainio

Space Physics · Cross-listed from gr-qc

Horizon-Scale Corrections to Black Hole Geometry from a Conserved Quantum Atmosphere

Kashif Ammar Yasir

Black holes are usually described either as classical geometries on which quantum fields propagate or as objects whose complete quantum description lies beyond semiclassical gravity. Hawking radiation already shows, however, that a black hole is not an exactly isolated system: the horizon carries a thermal scale and, after coarse graining, may be associated with fluctuations, dissipation and environmental correlations. Whether this horizon-scale openness can be encoded directly in the gravitational background, before any stochastic treatment of the metric, remains an open question. Here we answer it by introducing, for the first time, a conserved Hawking-scale anisotropic source representing the coarse-grained near-horizon atmosphere and solving the Einstein equations for a static black hole at fixed ADM mass. The dressed geometry has a renormalized mass function, a self-consistently shifted horizon and a modified surface gravity. Because the same lapse governs the horizon and timelike geodesics, the thermal response is accompanied by a correlated orbital restructuring: the effective potential is renormalized, the ISCO moves inward and the near-horizon residence time increases. The construction adds no Langevin force to a fixed Schwarzschild background; rather, it defines a deterministic dressed mean geometry, providing a controlled background on which stochastic metric fluctuations may subsequently be treated in the Einstein-Langevin framework. This establishes the deterministic mean-field sector as the necessary first step for future stochastic gravity programs addressing horizon-scale openness.
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Space Physics

Data-driven prediction of atomic-oxygen erosion yield in polymers from bulk physical properties

Youngwoo Choi, Doeun Koo, Seungbum Hong et al. (+1 more)

Atomic oxygen (AO) erodes polymer surfaces in low Earth orbit, but durability data are limited. We evaluated a regression ensemble trained on 37 MISSE-2 polymers using eight selected bulk properties and five elemental-composition ratios. Its archived leave-one-out R^2(log) was 0.768; this estimate is conditional on feature selection using the complete training table. For nine post-MISSE-2 polymers, the ensemble gave R^2(log) = -0.037 and all predictions were within a factor of two. The training arithmetic-mean baseline also met that tolerance for all nine, highlighting the limited discrimination provided by their narrow target range. Ground-based comparisons included four PLAVIS grades. For an out-of-training mystery polymer with undisclosed composition, the predicted erosion yield was within a factor of 1.92 of the ground-based measurement. Conflicting PLAVIS measurement records prevent a definitive residue-erosion ordering or ground-validation score. Thermal residue, SEM contrast and surface chemistry provide distinct observational evidence; they do not establish a protective-layer mechanism. The results support further evaluation of orbital-data screening models with reconciled measurement records and prospectively fixed inputs..
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All authors Youngwoo Choi, Doeun Koo, Seungbum Hong, Hyun Jung Kim

Monday 5 October

Space Physics · Cross-listed from astro-ph.SR

Fast and Differentiable MHD Surrogate for Solar Wind using Neural Operator

Prateek Mayank, Enrico Camporeale, Thomas E. Berger et al. (+2 more)

Global magnetohydrodynamic (MHD) simulations provide the complete plasma state of the heliosphere, but their computational cost limits applications requiring repeated model evaluations. We introduce SNOW (Solar Neural Operator for Wind), a fast and differentiable surrogate for global MHD solar wind. SNOW combines a rotational ballistic approximation, a spherical harmonic neural operator, and causal radial context to autoregressively propagate all eight MHD variables from 20 to 240 Rs through consecutive shell to shell transitions. Trained and evaluated using AWSoM simulations spanning a solar cycle, SNOW remains stable across the complete rollout. The model successfully reproduces the large scale plasma and magnetic field structures, including fast and slow wind streams, magnetic polarity sectors, vector orientations, fieldline connectivity, and bulk-flow structures. Additionally, the magnetic divergence and induction diagnostics remain comparable to the reference MHD solutions. The complete three-dimensional solution is generated in less than one second on a single GPU. These results demonstrate the feasibility of fast neural emulation of global MHD solar wind solutions while retaining physically meaningful plasma and magnetic field structure.
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All authors Prateek Mayank, Enrico Camporeale, Thomas E. Berger, Zhenguang Huang, Gabor Toth

Sunday 4 October

Space Physics

What Caused the Orbital Decay of the Twin Van Allen Probes to Diverge?

Ayisha M Ashruf, Ankush Bhaskar, C Vineeth et al. (+1 more)

The Van Allen Probes were launched into nearly identical orbits and experienced the same solar and geomagnetic environment, yet their post-mission lifetimes diverged dramatically. Probe A underwent rapidly accelerating orbital decay and reentered the atmosphere in March 2026, while Probe B remains in orbit. We investigate the cause of this divergence using reconstructed orbital trajectories, modeled thermospheric densities, and measures of low-altitude residence and atmospheric drag. We find that small differences in orbital evolution progressively increased Probe A residence time in the lower thermosphere, where the steep density gradient made additional low-altitude exposure increasingly important. Enhanced thermospheric density during periods of geomagnetic activity further amplified this difference, leading to greater drag and accelerating orbital decay of Probe A. Our results show how small differences in orbital evolution can be amplified through the coupled effects of thermospheric drag and space weather, producing substantially different orbital lifetimes even for twin spacecraft sharing nearly identical initial orbits.
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All authors Ayisha M Ashruf, Ankush Bhaskar, C Vineeth, Tarun Kumar Pant

Saturday 3 October

Space Physics · Cross-listed from astro-ph.SR

Deriving the Continuous $\beta$-FPUT Model for Decayless Solar Coronal Oscillations Directly from Resistive MHD

D. Tsiklauri

We present an analytical framework deriving the fluid-continuum $\beta$-Fermi-Pasta-Ulam-Tsingou ($\beta$-FPUT) system directly from a third-order resistive magnetohydrodynamics (MHD) expansion to explain persistent, decayless transverse oscillations observed in solar coronal loops. For a continuous wave field propagating along a longitudinal magnetic field with cross-field density variations, a multi-scale expansion demonstrates that quadratic $\mathcal{O}(2)$ advective and Maxwell tension terms vanish identically due to out-of-plane polarization symmetry. Instead, the quadratic longitudinal ponderomotive force drives field-aligned density modulations that back-react on the primary transverse wave, yielding a cubic $\mathcal{O}(3)$ restoring force. In the long-wavelength limit, the governing equations reduce to a fluid-continuum Modified Korteweg-de Vries (mKdV) system where cross-field profile variation provides the non-linear dispersive mechanism. We prove that this internal fluid mechanism establishes stable, amplitude-dependent frequency self-focusing, which phase-locks adjacent elements and prevents phase-mixing wave attenuation without requiring external steady driving parameterizations. This framework enables macro-scale coronal seismology, providing closed-form expressions to invert observed decayless wave-packet durations to compute the unresolved cross-field density gradient scale length ($L_x$) and the internal volumetric filling factor ($f_V$) without relying on traditional emission measure or spectroscopic line-ratio diagnostics. Much like famous Enrico Fermi's historic use of macro-scale displacements to estimate complex atomic explosion yields, this framework establishes a paradigm where monitoring macroscopic oscillation durations empowers observers to extract fine-scale, otherwise unresolvable waveguide properties.
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Space Physics · Cross-listed from astro-ph.SR

Measured energy exchange in coronal hole solar wind from its solar origins to the heliosphere

Yeimy J. Rivera, Alin R. Paraschiv, Samuel T. Badman et al. (+33 more)

Coordinated ground- and space-based remote observations are used to provide a comprehensive, multi-perspective view of the solar atmosphere that we connect with in situ measurements in the heliosphere centered around the April 8 2024 Total Solar Eclipse observed across North America. These near-contemporaneous, multi-wavelength datasets are used to directly derive the plasma parameters and compute an energy budget of a solar wind stream at its low-coronal birthplace (at an altitude of 1.05Rsun). The energy budget is also independently computed at and beyond the Alfvén surface from the in situ observations of the same stream. The total wave energy flux dominates the low-coronal budget (11 W m-2 Alfvén, 7 to 23 W m-2 in compressive MHD modes), while enthalpy (13 W m-2) and work done against gravity from 1.0Rsun (2.5 W m-2) make up the remainder. The total coronal energy budget is consistent with the total measured in situ by Parker Solar Probe if and only if compressive energy flux is included and attributed to the fast magnetosonic mode. Nearly all this thermal and wave energy is converted to ion heating, acceleration and gravitational potential energy within the Alfvén surface. The stream evolution is well-described as a thermal-pressure driven wind with additional energy deposited by MHD fluctuations. The observed evolution of the Alfvénic component of these fluctuations follows a near-dissipation-free curve below the Alfvén surface while deviating from it more strongly above this critical surface.
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All authors Yeimy J. Rivera, Alin R. Paraschiv, Samuel T. Badman, Alberto M. Vasquez, Federico A. Nuevo, Ryan J. French, Momchil Molnar, Roberto Susino, Zihao Yang, Marco Romoli, Richard A. Frazin, Michael L. Stevens, Stuart D. Bale, Deborah Baker, Jasper Halekas, Thomas A. Schad, Christopher J. Owen, Philippe Louarn, Jenna Samra, Giuliana de Toma, Daniela A. Lacatus, Giulio Del Zanna, Chad A. Madsen, Enrico Landi, Manolis K. Georgoulis, Amir Caspi, Éric Buchlin, Nour E. Raouafi, Luca Franci, Miho Janvier, Cooper Downs, Roberto Livi, Phyllis Whittlesey, Ali Rahmati, Davin Larson, Nikos Sioulas

Space Physics · Cross-listed from astro-ph.EP

How dust particles orbiting white dwarfs can reveal undetected co-orbiting exoplanets II. Exoplanets on elliptic orbits

Kyriaki I. Antoniadou and Dimitri Veras

Abridged. We aim to extend Paper I to the eccentric secondary orbit case and now analyse the elliptic restricted three-body problem (ERTBP). Our secondary masses include Ceres, Mercury, Earth, and Neptune so that we can help infer the presence of both large asteroids and planets through our analysis. We study dust particles on both planar (2D-ERTBP) and non-coplanar (3D-ERTBP) orbits. We computed families of 1/1 resonant symmetric and asymmetric periodic orbits in the 2D-ERTBP and 3D-ERTBP. Doing so produces novel results in their own right and diagnostic tools for precise guidance for our next steps. Based on them, we generated detailed phase portraits. Finally, we run suitably seeded $N$-body simulations to compare with the periodic orbits, and to provide observational links with debris close to WDs. New families of asymmetric periodic orbits, called $E^A_{41}$, $E^A_{42}$, and $E^A_{43}$ in the high-eccentricity 2D-ERTBP regime were discovered. They are generated by the new bifurcation point, $B_T^4$, along the new $A_2$ family, showcased in Paper I. Moreover, new isolated families of asymmetric periodic orbits, namely $E^A_{44}$, $E^A_{45}$, and $E^A_{46}$ were discovered. Families of short- and long- period asymmetric orbits starting from $L_4$, called $E^A_S$ and $E^A_L$, were also computed. In both the 2D- and 3D-ERTBP regimes, highly eccentric motion is exhibited for the dust particles in the majority of the families of either symmetric or asymmetric periodic orbits. The $N$-body simulations reveal that over ten years, the orbital period deviations of the dust are higher than in the circular restricted three-body problem (Paper I); in some architectures, Mercury-mass planets can regularly generate deviations exceeding $\sim$100 s, which potentially aids observational inferences of hidden asteroids or planets orbiting WDs.
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Thursday 1 October

Space Physics

A Student Sounding Rocket Experiment to Probe Electron Density in the Lower Ionosphere

Joshua Goodwill, Timothy Tomaszewski, Jarrod Bieber et al. (+17 more)

Earth's ionosphere is primarily generated by the Sun's ionization of atoms in the upper atmosphere. This plasma environment is highly dynamic, exhibits strong spatial and temporal, variations and significantly impacts power systems, navigation, and satellite and ground communications. The University of Delaware Ionospheric Probe (UDIP) was developed as a hands-on learning experience for University of Delaware students on the ionosphere itself and on the development of space technology. Students (mostly undergraduates) have led all aspects of the experiment including mission planning, electronics development, mechanical development, software development, and scientific data analysis. The present study is intended as a guide to readers on how the development of space and near-space flight missions can be successfully incorporated into an undergraduate physics curriculum. The fourth version of the experiment (UDIP-4) flew along with student experiments from across the USA on the 2024 RockSat-C sounding rocket, which was launched from NASA Wallops Flight Facility. During the flight, UDIP-4's Langmuir probe successfully measured the ionosphere's density profile – electron density as a function of altitude – up to an apogee of 114 km. Though the measured density profile agrees well overall with the predictions of theoretical models, UDIP-4 identified a thin layer of enhanced electron density at an altitude of approximately 110 km that is consistent with a sporadic E layer.
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All authors Joshua Goodwill, Timothy Tomaszewski, Jarrod Bieber, Carson P. Brown, Ashton Southwick, Samuel Auerbach, Sreenidhi Banda, Alex Bruce, Marisol Catalan Olais, Markos Duey, Ranyah Khan, Connor McCleery, Jonathan Rosado, Amanda Swenson, Matthew Ward, Jarod Dagney, David Sundkvist, John W. Bonnell, William H. Matthaeus, Bennett A. Maruca

Wednesday 30 September

Space Physics · Cross-listed from physics.plasm-ph

Normal-Field Evolution and the Breakdown of Classical Tearing in Current Sheets

Grzegorz Kowal and Diego A. Falceta-Gonçalves

Classical resistive tearing theory assumes a prescribed current-sheet equilibrium, but a finite normal magnetic field can evolve the background on the tearing timescale. For a transversely pressure-balanced Harris profile of initial half-thickness $a$ and asymptotic reconnecting-field magnitude $B_0$, threaded by uniform $B_n$ ($\xi=B_n/B_0$), we derive an exact evolution in ideal magnetohydrodynamics: counter-propagating Alfvenic fronts broaden the neutral layer and generate a central sheet-parallel flow with shear at its flanks. Inner-layer estimates recover $\xi_{\mathrm{crit}}\sim S^{-3/4}$ for breakdown of the classical resistive balance, where $S$ is the Lundquist number based on $a$. Numerical frozen-profile calculations show loss of central resistive dominance and decreasing tearing growth as the neutral layer expands. Eigenfunction comparisons at fixed wavenumber and predominantly Doppler-shifted propagation support a normal-field-modified continuation of classical tearing. The normal field supplies no net perturbation energy. Energy extraction from the reconnecting-field gradient weakens as the sheet broadens. The velocity-gradient contribution becomes comparable when the neutral-layer width approaches the initial sheet thickness, without reversing the decline in growth. For $S=10^6$, $\mathrm{Pr}_m=0$, and $\xi=10^{-4}$, the maximum growth rate falls by a factor of about ten from its initial value at neutral-layer half-width $w\simeq1.59a$, where the growth and broadening times become equal. Only about 0.18 additional upper-envelope e-folds are estimated between this crossing and $w/a=2$, where the growth rate is about 25 times smaller than its initial value. These results support dynamical suppression of further linear amplification over the sampled evolution, even though the instantaneous spectrum remains unstable.
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Space Physics

Revisiting magnetotelluric theory: layered induction and geoelectric fields

Dennies Bor

We review the magnetotelluric (MT) theory of a horizontally layered Earth under plane wave forcing and its use in calculating geoelectric fields. Starting from Maxwell's equations, we derive the diffusion approximation and the impedance recursion by matching electric and magnetic fields at layer boundaries. The equivalent transmission line connects the surface impedance to attenuation with depth, apparent resistivity, phase, and the electric response to a magnetic time series. Three evaluations accompany the derivation, each against its own reference. First, under the storm of 10 and 11 May 2024, electric fields calculated from layered models fitted to measured impedance tensors differ from those calculated from the tensors by a median vector error of 46% across 1614 EarthScope MT sites with sufficient period coverage. Reducing each tensor to its antisymmetric projection alone gives a median of 46%, while the layered fit and numerical processing give medians of 1.9% and 1.3%. Second, the magnetic field reconstructed at each of 20 withheld observatories from the remaining network has a median vector error of 48%. In a common electric field comparison, the magnetic reconstruction gives the larger electric vector error in 96% of 32,280 observatory-tensor pairs, with medians of 93% against 46% for the layered representation. Third, when conductivity inferred at MT sites is interpolated by kriging into withheld regions, the median relative error of the predicted impedance is 57.3%, and 11 of 149 withheld sites have an apparent resistivity discrepancy of a factor of 100 or more at one or more periods. The vector comparison retains differences in the amplitude and direction of the electric field that are relevant to calculating induced voltages along transmission line routes.
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Tuesday 29 September

Space Physics · Cross-listed from physics.plasm-ph

Effects of Alfvénicity on the Compressible Energy Cascade in Magnetohydrodynamic Solar Wind Turbulence: Evidence from Parker Solar Probe, Solar Orbiter, and WIND observations

Nahuel Andrés, Carlos A. Gonzalez and Norberto Romanelli

The compressible MHD energy cascade in the solar wind is shaped by Alfvénicity, plasma fluctuations, and proton temperature, yet how these factors regulate the relative weight of compressible and incompressible energy transfer across heliocentric distances remains poorly understood. We apply compressible and incompressible exact relations to a large sample of 2-hour intervals from WIND (1~au), Parker Solar Probe ($<0.25$~au), and Solar Orbiter (0.3–1~au), classifying intervals as Alfvénic ($|\sigma_c|>0.75$) or non-Alfvénic ($|\sigma_c|<0.25$) and by wind speed, and examine the Yaglom-like and purely compressible components of the compressible cascade. Velocity fluctuation amplitude is the strongest predictor of the compressible cascade rate $\langle|\varepsilon_c|\rangle$, followed by density and magnetic field fluctuations. $\langle|\varepsilon_c|\rangle$ and $\langle|\varepsilon_i|\rangle$ are tightly correlated in all regimes, with their ratio organized by Alfvénicity and wind speed: non-Alfvénic and Alfvénic fast winds cluster along $\langle|\varepsilon_c|\rangle=\langle|\varepsilon_i|\rangle$, while Alfvénic slow wind shows a systematic excess consistent with internal energy contributions. The largest $\langle|\varepsilon_c|\rangle$ systematically occur in hotter intervals, with a two-decade increase from cool to hot events in Alfvénic slow and non-Alfvénic wind, a trend carried mainly by the purely compressible term, while the dominant Yaglom-like term controls the overall cascade magnitude. Alfvénicity and wind speed thus govern the efficiency of turbulent energy transfer across heliocentric distances, and the tight coupling between compressible and incompressible rates points to the need for compressible, multi-fluid descriptions of the solar wind dissipation budget.
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Monday 28 September

Space Physics

Temporal Correlation between Ionospheric Storm-Enhanced Density Plume and Plasmaspheric Plume Occurrence

Xiangning Chu, Shunrong Zhang, Jacob Bortnik et al. (+5 more)

We present a statistical evidence of a temporal correlation between ionospheric storm-enhanced density (SED) and plasmaspheric plumes during magnetic storms. We identified SED plumes in 75 storms between 2010-2024 with sufficient total electron content (TEC) coverage. We also identified plasmaspheric plumes during these storms using a plasmapause asymmetry (PPA) index derived from the machine-learning-based DEN3D model. We found that all SED plumes coincided with plasmaspheric plumes. The start and end times of both phenomena exhibit near-zero lag within a half-hour delay, confirming their synchronized evolution. For the first time, superposed epoch analyses reveal that plume onsets align with solar wind driving and geomagnetic activity, including peaks in the electric field, coupling function, auroral electrojet indices, and the asymmetric ring current index, all of which facilitate plume formation. This work provides timely new insights into magnetosphere-ionosphere coupling processes and demonstrates the utility of machine-learning-based diagnostics for space physics/weather.
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All authors Xiangning Chu, Shunrong Zhang, Jacob Bortnik, Naomi Maruyama, Jerry Goldstein, Kausik Chatterjee, David Malaspina, Phil Erickson

Space Physics

Spectral Properties of Solar Wind Charge Exchange from Earth's Magnetospheric Boundaries: MHD and Test Particle Simulations

A. Ramachandran, R. T. Desai, H. L. Norman et al. (+6 more)

The Solar Wind Charge Exchange (SWCX) mechanism, where X-rays can be generated through interactions between heavy, highly charged solar wind ions and neutral atoms, offers an opportunity to observe the large-scale transfers of energy and momentum through the Sun-Earth system. In this study, we simulate SWCX signatures from Earth's outer boundaries using Gorgon global magnetohydrodynamic (MHD) simulations combined with kinetic particle-based simulations which we call the X-ray Imaging of the Magnetosphere (XIM) framework. The XIM-predicted emissivities agree with the predictions of the MHD model, producing enhanced emissions from the magnetosheath and cusp regions, but several differences are apparent. Compared with MHD, XIM shows enhanced structuring in the magnetosheath and notable enhanced emissions along the magnetopause associated with betatron acceleration. The results also evidence species-specific spatial variations, which are shown to vary compared to anticipated relative abundances in the solar wind and ion-specific properties. These simulations provide new insights into the underlying dynamics of SWCX at the Earth's outer boundaries, which can be used to understand what might be observed using X-ray observatories in space, such as the recently launched SMILE mission.
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All authors A. Ramachandran, R. T. Desai, H. L. Norman, Y. Tong, D. Bewicke, S. Nitti, J. A. Carter, J. P. Eastwood, J. P. Chittenden

Space Physics · Cross-listed from astro-ph.EP

The precipitation of protons and electrons in Jupiter's auroral regions: a statistical comparison based on Juno/JEDI data

B. Benmahi, N. André, V. Hue et al. (+8 more)

Energetic electrons dominate the energy precipitated into Jupiter's auroral regions, but protons precipitate along the same field lines, with a contribution that remains poorly constrained. We statistically compare the precipitating energy flux of protons and electrons in two of Jupiter's auroral sub-regions, the polar (PE) and main (ME) emission regions. We use Juno/JEDI data from PJ3 to PJ66. The magnetic footprint of the spacecraft, computed with the JRM33 and CON2020 field models, is assigned to one of the two sub-regions, and the precipitating energy flux of each species is obtained by integrating over the loss cone the mean differential intensity measured within it. In both sub-regions, the median proton energy flux is 52 to 223 times lower than that of the electrons, and the total precipitated proton power is less than 2% of the electron power. Proton fluxes are broadly distributed across the sub-regions, with higher values in the ME than in the PE. Protons play a secondary role in Jupiter's auroral energy budget, radiating an estimated 5 to 9 GW in the UV per sub-region, pending a dedicated proton transport modelling. Their Doppler signature in the red wing of the Lyman-$\alpha$ line, undetected by HST and difficult to access with Juno/UVS, is a key observable for the upcoming Juice and Europa Clipper missions.
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All authors B. Benmahi, N. André, V. Hue, Z.-Y. Liu, G. Gronoff, B. Mauk, B. Bonfond, T. Stallard, M. Blanc, M. Devinat, M. Barthélémy