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Physics Physics Space Physics

physics.space-ph Watch Space Physics

Monday 28 September

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

Energy distributions of precipitating electrons in Jupiter's auroral regions from combined Juno/JADE and Juno/JEDI measurements

B. Benmahi, V. Hue, N. André et al. (+17 more)

Jupiter's auroras are produced by magnetospheric electrons precipitating into its atmosphere. Juno/JADE and Juno/JEDI together measure these electrons from 100 eV to 1 MeV. However, their auroral spectra are poorly reproduced by the widely used kappa distribution, hereafter the classical single-kappa distribution. We aim to statistically characterize the energy flux distributions of precipitating auroral electrons and to derive a new phenomenological 4-kappa distribution better suited to JADE+JEDI data. We build mean energy flux distributions in six auroral sub-regions (polar, main, and outer emissions in both hemispheres), combining JADE and JEDI data from PJ3 to PJ35, mapped to the SIII frame with the JRM33 model including the current sheet. We fit them using MCMC with the classical single-kappa and 4-kappa distributions. The mean distributions show a monotonic power-law decay with an energy cutoff beyond ~500 keV in most sub-regions, although some individual spectra depart from it at intermediate energies. Mean energies range from ~21 to ~119 keV, and energy fluxes from ~9.5 to ~28.7 mW/m$^2$. The classical single-kappa fit fails in all sub-regions, with $\kappa$ converging to the lower bound of its prior range. We therefore introduce the 4-kappa distribution, a linear combination of four classical single-kappa distributions modulated by an exponential high-energy cutoff, which accurately fits all six sub-regions. At equal energy flux and mean energy, transport simulations show that the 4-kappa distribution deposits energy at lower altitude than the classical one and distributes it differently along the vertical, with implications for the UV color ratio, atmospheric chemistry and thermal structure, and ionospheric conductances. This distribution provides an analytical framework for realistic modeling of electron precipitation and UV auroral emissions at Jupiter.
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All authors B. Benmahi, V. Hue, N. André, B. Bonfond, M. Blanc, Z.-Y. Liu, B. H. Mauk, F. Allegrini, G. Clark, M. Devinat, G. Gronoff, T. Le Liboux, M. Barthélémy, C. Lefour, T. Cavalié, B. Benne, T. Gautier, T. Briand, J. A. Noble, J. A. Sinclair

Space Physics

P2D - A Two-Dimensional Multi-Spacecraft Solar Wind Persistence Model

Daniel Milošić, Manuela Temmer, Stephan G. Heinemann et al. (+2 more)

The background solar wind is a key component in space weather forecasting, as it contains geoeffective high-speed streams and provides the medium through which coronal mass ejections propagate and evolve in interplanetary space. Due to the solar rotation and the slow evolution of large-scale solar wind structures, solar wind properties exhibit an autocorrelation with a period of roughly 27 days, particularly at solar minimum. We made use of this property to develop a solar wind persistence model with input from multiple spacecraft (Solar Orbiter, Parker Solar Probe, STEREO-A, STEREO-B and the OMNI database). The model ballistically propagates in-situ data from the position of their measurement radially away from the Sun, as well as longitudinally with the solar rotation rate, producing 2D maps of solar wind parameters. These can be extracted at any point in the heliosphere for a solar wind reconstruction. From Earth's perspective, the reconstruction performs with an MAE of 65.41 km/s and 3.51/cm^3 for speed and density, respectively. During high-speed streams, the peak hit rate is 50% and 48% for speed and density. It performs best during times when there are spacecraft located between Earth and Lagrange point L5. During these times, the mean absolute error of the predicted solar wind speed decreases by roughly 35% in comparison to the benchmark 27-day persistence model. Therefore, future L5 missions like Vigil are expected to provide a robust basis for reliable persistence forecasts.
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All authors Daniel Milošić, Manuela Temmer, Stephan G. Heinemann, Mathew Owens, Stefan J. Hofmeister

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

Numerical analysis of electron density and response time delay during solar flares in mid-latitudinal lower ionosphere

Sayak Chakraborty and Tamal Basak

Impacts of solar flare vary at different parts of the lower ionosphere depending on its proximity to the direct exposure of incoming solar radiation. The quantitative analysis of this phenomenon can be attributed to the solar zenith angle (chi(t)) profile over the ionosphere. We numerically solve the electron continuity equation to obtain the lower ionospheric electron density profile (Ne(t)). The electron production rate (q(t)) is governed by the (i) X-ray profile (phi(t)) of the flare, (ii) chi(t)-values during the flare occurrence, etc. For analyzing the X-ray profile during flares, we use the GOES-15 satellite observations. Since we are working on an electron continuity equation based simplified ionospheric model, we confined our analysis to the comparatively stable mid-latitude ionosphere only. We choose three flares each from C, M, and X-classes for Ne(t)-profile computation. We observe that temporal Ne(t)-profiles differ when computed for the lower ionosphere over different discrete latitudes. Further, we compute the spatial Ne(t)-profile across the mid-latitude region at the time when phi(t) = phi_max. Now we assume that these flares repeat themselves every day of a year (DoY) at the same time of a day and we compute Ne(t)-profiles for each day. We found a seasonal effect on the Ne(t)-profile due to solar flare. Further, we investigate the response time delay (Delta t) of the lower ionosphere, which is the time difference between incidence of X-ray and the respective change in Ne(t)-profiles during solar flares. Strong seasonal effects on Ne(t)-profile and Delta t are the unique results of this work.
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Sunday 27 September

Space Physics

An autonomous approach to model daytime behavior of sub-ionospheric VLF signals over short and medium propagation paths in India

Sayak Chakraborty, Tamal Basak, Sourav Palit et al. (+1 more)

We present an autonomous model to simulate the daytime variation of sub-ionospheric Very Low Frequency (VLF) signal amplitude, beginning with the computation of the D-region electron density by numerically solving the electron continuity equation (ECE). From the resulting altitude-dependent electron density profile (Ne), we extract Wait's ionospheric parameters (h' and beta) using a log-linear fitting method. The study focuses on two VLF propagation paths (one short and one medium in length) in India, originating from the VTX (18.2 kHz) transmitter. The model employs the Long Wave Propagation Capability (LWPC) framework to reproduce the daytime VLF signal amplitude profile. It accurately captures the daytime variations observed at the Bengaluru (BAN) station, where the ground-wave component is dominant, as well as at Khukurdaha, WB (KHK). A quantitative comparison between the simulated (Asim) and observed (Aobs) amplitudes shows good agreement, supporting the physical consistency and potential predictive capability of the proposed approach.
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All authors Sayak Chakraborty, Tamal Basak, Sourav Palit, Sandip K. Chakrabarti

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

Modeling of the variability of D-region ionospheric electron density during solar cycle-24

Sayak Chakraborty, Sourav Palit, Semontee Deb et al. (+1 more)

Solar cycle variation of earth's atmosphere, particularly the ionosphere is of particular interest in the field of space science and space weather studies. In this article, we present the outcome of our detailed quantitative study on solar cycle variation of lower ionospheric properties using numerical investigation. First, we seek to model and compare the collective D-region ionization rates (q's) due to the individual contributions from the ionizing sources, namely, (a) solar extreme ultraviolet (EUV) radiation including the Lyman-alpha irradiation and (b) solar X-ray irradiation throughout the 24th solar cycle (C24). Then, we compute the electron density (Ne) profiles using the ionization rates. We report significant solar cycle variation in ionization rate and electron density profiles for the entire span of C24. We use the sunspot number (SPN) profile to substantiate the finer details of Ne profile during C24. For the segments of the D-region above two different geographic coordinates, we report that Ne profiles show a consistent "dual peak" nature. It is very similar to the SPN profile during C24. As a next-order validation, we compare our modeled Ne profiles with their IRI-2020 counterpart (Ne,iris). Their overall trends are found to be in agreement. Finally, we discuss the response of the D-region in terms of Ne due to C24. The work lays the foundation for our upcoming studies on D-region response to solar cycle variation with Very Low Frequency (VLF) observation.
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All authors Sayak Chakraborty, Sourav Palit, Semontee Deb, Tamal Basak

Friday 25 September

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

Negative and Positive Cascade Rates of Slow Alfvénic Turbulence in Switchback and Non-switchback Intervals: Wind Observations

Sofiane Bourouaine

We estimate the turbulent cascade rate in imbalanced Alfvénic turbulence in the slow solar wind using a Politano–Pouquet-based approach that does not require an isotropic assumption. We analyze selected 8-hour intervals provided by Wind spacecraft. These intervals are characterized by near-homogeneity, weak velocity shear, and imbalanced Alfvénic fluctuations, and are classified as switchback or non-switchback depending on the angular spread of the magnetic field relative to the mean field. Switchback intervals are identified by large magnetic-field rotations, whereas non-switchback intervals exhibit only small angular deviations. Our results show that non-switchback intervals exhibit a positive total cascade rate and power spectra consistent with a $-3/2$ scaling, indicative of a forward energy cascade. In contrast, switchback intervals are characterized by a negative total cascade rate (inverse cascade), and by steeper power spectra with a spectral index of approximately $-1.6$. This indicates that large magnetic-field rotations can substantially modify the scale-to-scale energy transfer in Alfvénic slow solar wind. The results suggest that switchbacks may be associated with additional physical processes, such as local instabilities, or reconnection-related structures, that alter the direction and magnitude of the turbulent cascade. These findings may help explain previous reports of negative cascade rates in imbalanced Alfvénic solar-wind turbulence.
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Space Physics

Electric Potential Patterns Forecasting in the Southern Hemisphere with Deep Learning Techniques

Francesco Pio Ramunno, Simone Mestici, Igino Coco et al. (+5 more)

Space weather disturbances driven by the solar wind can degrade satellite navigation, disrupt radio communications, and threaten power infrastructure, making accurate forecasting of the high-latitude ionosphere's response a critical operational need. Existing approaches, empirical climatological models and physics-based magnetohydrodynamic simulations, either smooth out the ionosphere's time-dependent, non-linear response or are too computationally expensive for real-time use, while prior machine learning efforts have mostly targeted scalar indices rather than the full spatial structure of ionospheric convection. Here we train and compare three deep learning architectures, a probabilistic diffusion model conditioned on multi-variate solar wind and interplanetary magnetic field measurements at the L1 Lagrange point, an unconditioned diffusion ablation, and a deterministic U-Net baseline, to forecast Southern Hemisphere high-latitude electric potential maps derived from SuperDARN radar observations. Using five years (2020–2025) of SuperDARN data synchronised with DSCOVR L1 measurements, we evaluate the models under a single-pass regime, an extended autoregressive rollout of up to 350 frames, and an out-of-distribution case study on the intense March 2015 St.\ Patrick's Day storm, unseen during training. We find that the relative advantage of the deterministic and probabilistic approaches is not fixed: the deterministic model is competitive over short horizons and calm conditions, while the diffusion model's advantage grows and eventually dominates as the forecast horizon lengthens and the event becomes more dynamic, evidence that probabilistic, sample-based generative models are the more promising direction for operational, long-horizon space weather forecasting.
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All authors Francesco Pio Ramunno, Simone Mestici, Igino Coco, Maria Walach, Stefano Massetti, Maria Federica Marcucci, Brandon Panos, André Csillaghy

Space Physics · Cross-listed from cs.LG

Self-Supervised Representation Learning: From Spectral Foundation Models to Auroral Emission Spectra

Matthieu Le Lain, Gaël Cessateur and Sébastien Lefèvre

Auroral spectrographs such as the Auroral Spectrograph In Skibotn (ASIS) record hundreds of thousands of emission spectra, but only a few hundred can be labelled by an expert. To exploit the rest, we pretrain a 1D Vision Transformer with a masked autoencoder on 223,000 unlabelled spectra. Without labels, its representation recovers the emission-line intensity ratios that physicists use to diagnose the precipitating particles (R^2 0.91 vs. 0.77 for an untrained control) and, under one linear probe, classifies as well as 13 features designed by experts. Fine-tuned, the model outperforms the previous supervised auroral classifier on its own benchmark (macro-AP 88.5 vs. 77.8), reaches 0.870 mAP, and exceeds the same architecture trained from scratch by +0.159 with 10% of the labels; attribution shows that it uses both N2+ bands. Could an existing pretrained model replace it? Two astronomical spectral foundation models and a time-series model transfer according to their spectral window: SpectraFM, trained in the infrared, falls below the untrained control, whereas SpecFormer, trained in the optical, approaches in-domain pretraining without reaching it.
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Thursday 24 September

Space Physics · Cross-listed from eess.SY

From Routing Delay Shifts to Silent Data Corruption: Neutron-Induced SEU Effects in AXI-Based Zynq UltraScale+ MPSoCs

Mostafa Darvishi

SRAM-based FPGA system-on-chip devices are vulnerable to single-event upsets (SEUs) in configuration memory, which may perturb programmable routing resources and degrade communication fabrics. In modern Zynq UltraScale+ MPSoCs, such routing disturbances can introduce small propagation delay shifts that remain logically transparent yet compromise AXI-based data transfers and lead to silent data corruption. Although routing delay degradation and AXI interconnect failures have been studied independently, their experimental correlation under neutron irradiation has not been established. This work presents a cross-layer investigation on a ZCU104 platform integrating routing-dominated delay sensors with an AXI interconnect benchmark comprising replicated accelerators. Neutron irradiation experiments were conducted on the fully operational system, while a frame-level configuration fault injector implemented via the internal configuration access port enables controlled upset emulation. Measured routing delay events are statistically correlated with communication failures, and cross-sections for both timing shifts and AXI malfunctions are derived. The results experimentally demonstrate how neutron-induced routing perturbations propagate into system-level silent data corruption in UltraScale+ MPSoCs, providing insight for resilience-oriented AXI-based design in neutron-rich environments.
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Wednesday 23 September

Space Physics · Cross-listed from cs.LG

PISCES: Physics-Informed Solar-wind Convolutional autoEncoder for Space-weather Anomaly Detection and Early Warning

Kevin Lee and Alison J. March

Space weather early warning depends on detecting solar wind transients in in-situ measurements at the first Sun-Earth Lagrange point (L1), before they reach Earth. Fixed thresholds can miss combined magnetic and plasma structure, and many learning methods provide a single anomaly score. We present the Physics-Informed Solar-wind Convolutional autoEncoder for Space-weather (PISCES), a convolutional autoencoder trained without catalog labels on OMNI solar wind measurements under physics constraints. Its loss includes magnetic field consistency, an empirical relation between temperature and velocity, the Parker spiral angle, and penalties on changes between consecutive one-minute samples in derived quantities calculated from the reconstruction. At inference, PISCES separates the anomaly score into magnetic and plasma reconstruction errors, physics relations, and residual corrections, and reports the magnitude of each contribution. Attenuation of the skip connections, selected on validation data, improves average precision for the trained models, while the untrained scores remain nearly the same. The trained models also give a more consistent ordering of these physical contributions. After smoothing with a trailing median, the alarms can precede independently observed sudden commencements, including positive sudden impulses.
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Space Physics · Cross-listed from astro-ph.EP

Kelvin-Helmholtz vortices in the Martian +E hemisphere downstream of crustal magnetic anomalies

Junxi Niu, Tong Dang, Jiuhou Lei et al. (+6 more)

At unmagnetized planetary bodies, the Kelvin-Helmholtz (KH) instability at the solar-wind boundary is a key driver of atmospheric escape, fundamentally shaping long-term climate evolution. This shear-driven plasma mixing is theoretically predicted to be asymmetric, strongly favoring the hemisphere where the solar-wind electric field points toward the planet (-E hemisphere). Here we report the observation of a coherent train of fully developed KH vortices in the traditionally unfavorable +E hemisphere of Mars, using in-situ MAVEN measurements. Contemporaneous upstream constraints from Tianwen-1 confirm a steady interplanetary magnetic field, indicating sustained shear-driven growth rather than a transient boundary response. We find that these vortices developed within an expanded, weak-field boundary layer downstream of strong southern crustal magnetic anomalies. Our analysis suggests that regional boundary structuring can override the large-scale hemispheric preference to facilitate localized KH growth. These findings demonstrate that shear-driven escape pathways can operate in traditionally unfavorable regions, altering our understanding of atmospheric volatile loss at weakly magnetized planets.
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All authors Junxi Niu, Tong Dang, Jiuhou Lei, Binzheng Zhang, Wenya Li, Binbin Tang, Junjie Chen, Sudong Xiao, Tielong Zhang

Tuesday 22 September

Space Physics

The Localized 12-hour Wave Over Alaska: Leveraging Meridional Wind Measurements From the Sodium Lidar

Sophie R. Phillips, Katrina Bossert, Komal Kumari et al. (+3 more)

The 12-h wave in meridional winds in the mesosphere and lower thermosphere (MLT) during the solar minimum 2018-2019 Arctic winter is investigated using sodium lidar observations at Poker Flat Research Range (PFRR), Chatanika, Alaska (64N,147W). Nightly 12-h wave amplitudes increased significantly during December-January, with amplitudes exceeding 130 m/s above 97 km on several days. This was more than double the 12-h wave amplitudes observed outside this time period. Meteor radar winds over Chatanika also showed significant increase in meridional wind 12-h wave amplitudes at altitudes between 82 and 97 km during this time period with lower amplitudes than lidar measurements. The strong variation in 12-h wave amplitudes was not correlated with SME index, though the largest amplitudes coincided with the sudden stratospheric warming (SSW) in early January. Measurements were compared to a seasonal WACCM-X model run and four days of HIAMCM. For the four dates of available HIAMCM data, 12-h wave amplitudes over Chatanika were found to be similar between both HIAMCM and WACCM-X and the lidar below 97 km, with amplitudes measured by lidar exceeding the models at altitudes between 97-105 km. All measurements followed a similar seasonal trend with increasing amplitudes at the end of December/early January. Fits of SW2 from WACCM-X show the SW2 tidal amplitude following similar seasonal trends to 12-h wave measurements. These high-resolution lidar measurements indicate that localized 12-h wave amplitudes are larger than previously reported by studies using meteor radar measurements.
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All authors Sophie R. Phillips, Katrina Bossert, Komal Kumari, Erich Becker, Richard L. Collins, Nicholas Pedatella

Space Physics

First Observation of a Polar Coronal Hole-like Fast Solar Wind Stream in the Sub-Alfvénic Solar Corona: an Analysis of Turbulence Properties

Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus et al. (+2 more)

Parker Solar Probe, near its 23rd perihelion in March 2025, sampled an extended interval of sub-Alfvénic solar wind likely originating from a large equatorial coronal hole. At heliocentric distances of approximately 10 solar radii, with speed mostly above 400 km/s, this interval is a first example of “polar coronal hole-like (PCH-l) fast" solar wind observed in the sub-Alfvénic solar corona. We characterize the turbulence properties of this unique interval using Parker Solar Probe measurements. Despite being sampled well inside the nominal Alfvén surface, the turbulence appears to be already well developed while remaining strongly transverse and highly imbalanced, exhibiting a large cross helicity. These observations provide new constraints on the development and evolution of solar wind turbulence within the lower corona.
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All authors Riddhi Bandyopadhyay, Sujan Prasad Gautam, William H. Matthaeus, Yeimy J. Rivera, Samuel T. Badman

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

PROSWIN: Probabilistic Solar Wind Speed Forecasting Using Deep Distributional Regression From Solar Images

Daniel Collin, Yuri Shprits, Luca Chiarabini et al. (+3 more)

Accurately predicting fast solar wind conditions is challenging, as uncertainties are large and unquantified by traditional single-value prediction models. In particular, the risks of high-speed solar wind streams (HSSs), which can cause damage to technological infrastructure, cannot be reliably assessed without probabilistic forecasts. We present PROSWIN, a probabilistic machine learning model that forecasts the hourly solar wind speed (SWS) at Earth with a four-day lead time. The approach combines solar images and magnetograms using a deep neural network coupled to a distributional regression algorithm. Because standard error metrics underweight the relevance of HSS peaks, we further introduce the prediction score, a model-selection metric that jointly rewards timeline and HSS peak accuracy. On 14 years of data, our forecast achieves very well-calibrated uncertainties (<1% average deviation). Using the continuous ranked probability score (CRPS), a metric that assesses distributional accuracy, we obtain a timeline CRPS of 41.0 km/s, an HSS peak CRPS of 45.3 km/s, and a prediction score of 42.3 km/s. We find that the 171 Å channel is an important complement to the typically used 193 Å and 211 Å channels and that the prediction score for model selection improves the applicability of the model. Compared to selected models from the literature, ours is the only one that is accurate for both timeline and HSS peak values, rather than trading one off against the other. These results support the advantages of probabilistic over single-value solar wind models. The introduced methods are also transferable to other forecasting problems.
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All authors Daniel Collin, Yuri Shprits, Luca Chiarabini, Stefan J. Hofmeister, Nadja Klein, Guillermo Gallego

Monday 21 September

Space Physics · Cross-listed from eess.SP

Beyond Legacy L1 C/A: Characterizing Advanced Multi-Frequency Spoofing Against Multi-Frequency GPS Receivers for Autonomous Navigation

Minhaj Uddin Ahmad, Muhammad Sami Irfan, Sagar Dasgupta et al. (+2 more)

Autonomous vehicles increasingly rely on high-end multi-frequency GNSS receivers that track modernized civil signals, such as L2C, L5, and L1C, alongside legacy GPS L1~C/A. Although multi-frequency operation improves robustness against natural error sources, its resilience against synchronous multi-band spoofing attacks remains insufficiently characterized. This paper presents a method for quantifying the inter-band alignment accuracy required for a coherent spoofer to evade cross-frequency consistency monitoring that a resilient receiver may employ. As a foundational study, the presented method is implemented and evaluated using the GPS L1 C/A and L2C signal pair within a controlled software-defined environment. This environment encompasses deterministic signal synthesis, programmable inter-band code offsets realized through fractional-delay filtering, and processing by a dual-frequency GNSS-SDR receiver. An inter-frequency pseudorange-difference consistency detector is defined and calibrated using a constant-false-alarm-rate (CFAR) approach, yielding a threshold of approximately 19 m at a false-alarm probability of $10^{-3}$. Signal fidelity and receiver capture are verified through correlation-function analysis using a multi-tap correlator bank. The inter-band code offset is then swept from one code chip to 0.005 chips to characterize detector performance. Results show that a perfectly aligned coherent attack yields a detection probability of zero, while detection probability increases rapidly with inter-band misalignment, reaching approximately 50% at 0.05 chips (about 15 m) and approaching unity for offsets of 0.2 chips or greater. These results quantify the alignment precision required for successful coherent dual-frequency spoofing and establish a practical framework for future evaluation of L5, L1C, and hardware-based multi-frequency spoofing scenarios.
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All authors Minhaj Uddin Ahmad, Muhammad Sami Irfan, Sagar Dasgupta, Mizanur Rahman, Thejesh N. Bandi

Sunday 20 September

Space Physics

Predicting low-latitude ionospheric Total Electron Content (TEC) over the Indian sector under variable space weather conditions using solar wind parameters

Sumanjit Chakraborty, Gopi K. Seemala and A. P. Dimri

Accurate prediction of ionospheric Total Electron Content (TEC) during geomagnetically disturbed conditions remains challenging, particularly when empirical models perform poorly during storms and neural network (NN) approaches rely explicitly on geomagnetic indices such as Kp/Ap or Dst/SYM-H. In this study, we develop an NN-based model to predict TEC variations over the Indian longitude sector without incorporating geomagnetic indices as inputs. The model is trained on the full-year (2024) Global Ionospheric Map (GIM) TEC dataset at a 15-minute cadence, together with solar wind parameters: Interplanetary Magnetic Field (IMF) $B_z$, velocity ($V_{sw}$), and density ($N_p$), along with the F10.7 cm solar radio flux. Seasonal and diurnal variability are represented using sinusoidal transformations of Day of Year (DOY) and hour of day (HOD). An optimized architecture with 96 hidden neurons yields strong training performance ($R^2$ $\sim$ 0.96, RMSE $\sim$ 5.4, and MAE $\sim$ 3.8 TECU). Independent predictions for the year 2025 demonstrate robust generalization under both quiet and geomagnetically active conditions. Quiet-time residuals are generally confined within $\pm$10 TECU, while during moderate and strong storm-time conditions, the model maintains comparable error bounds across most of the Indian region, despite not being trained on geomagnetic indices. The results indicate that solar wind parameters, combined with the F10.7 solar flux and cyclical temporal encoding, contain sufficient information to reproduce geomagnetic storm-time TEC variability. This study therefore demonstrates the applicability of the proposed approach for regional TEC prediction and ionospheric nowcasting, with potential applications in GNSS positioning, satellite navigation, radio communication systems, and the future development of operational ionospheric forecasting tools.
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Space Physics

Interhemispheric differences in field-aligned currents, ground magnetic perturbations, and TEC during the geomagnetic storms of May and October 2024

Sumanjit Chakraborty and Gopi K. Seemala

This study investigates storm-to-storm variability and hemispheric differences in magnetosphere-ionosphere (MI) coupling during the extreme (G5) geomagnetic storm of May 10-11 and the severe (G4) storm of October 10-11, 2024. Global field-aligned current (FAC) patterns derived from the Active Magnetosphere and Planetary Dynamics Response Experiment (AMPERE), together with conjugate observations from ground-based magnetometers within the SuperMAG network and Global Positioning System (GPS)-derived total electron content (TEC), are analyzed to examine high-latitude electrodynamic and ionospheric responses in both hemispheres. The May event exhibits broad and relatively organized Region 1/Region 2 FAC systems encircling the polar caps across multiple local time sectors, accompanied by intervals of correspondence in conjugate magnetic perturbations and structured TEC enhancements with temporal offsets between hemispheres. In contrast, the October event shows more localized, asymmetric, and uneven FAC morphology with pronounced hemispheric and dawn-dusk asymmetries, together with greater divergence in conjugate magnetic responses and spatially heterogeneous TEC variability. These differences are consistent with enhanced mesoscale variability and asymmetric current closure under storm-time conditions. Overall, the results highlight that even under similarly strong solar wind driving, the coupled MI system can exhibit substantially different spatial organization and interhemispheric coupling, reflecting the combined influence of FAC morphology, ionospheric conductance, and local electrodynamic conditions.
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Friday 18 September

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

Interactions Between Two Magnetized Plasma Pressure Filaments: Drift-Alfvén Modes and Transport

Thomas Simala-Grant, Scott Karbashewski, Richard Sydora et al. (+1 more)

A set of experiments on merging dynamics of localized magnetized plasma pressure filaments in close proximity has been carried out in a large linear magnetized plasma device. A two filament configuration is used to determine the separation scale of cross-field interaction. Fluctuation analysis of the ion saturation current confirms the presence of unstable drift-Alfvén modes on each filament which are predominantly driven by the steep electron temperature gradient. When the filaments are separated a distance of approximately five times the size of a single filament or greater, no interaction is observed and the drift-Alfvén modes remain uncoupled. When brought closer together, significantly stronger interaction occurs with transfer of charge and energy, leading to the generation of inter-filament electric fields. This has the effect of rotating the filaments and influencing the merging dynamics. When the filaments are asymmetrically heated, the cooler filament becomes wrapped around the other, and the drift-Alfvén modes become fully coupled in a global mode structure. Transport between the filaments is explained in terms of E x B drift and the local potential wells of the filaments, and drift-Alfvén mode coupling occurs when the filaments are brought within the distance of a collisionless skin depth.
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All authors Thomas Simala-Grant, Scott Karbashewski, Richard Sydora, Bart Van Compernolle

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

Stability Analysis of the Proton Hammerhead Distribution Observed by Parker Solar Probe: Linear Theory and Fully Kinetic Simulations under Idealised Conditions

L. Pezzini, J. L. Verniero, F. Bacchini et al. (+3 more)

The non-adiabatic heating of the slow Solar Wind (SW) remains an open problem, with wave–particle interactions as a primary candidate mechanism. Novel in situ Parker Solar Probe (PSP) observations reveal strongly perpendicular anisotropic velocity distribution functions (VDFs), called "hammerhead", correlated with intense wave activity. These VDFs are systematically measured at the Heliospheric Current Sheet (HCS), making the hammerhead an important kinetic signature of the slow SW. In this work, we employ a fully kinetic particle-in-cell approach, complemented by a linear Vlasov solver to cross-validate the simulation results, to investigate the stability of these VDFs, the timescales over which they evolve, and their interaction with plasma waves. Our main findings indicate that the hammerhead distribution is primarily susceptible to drift-type instabilities, while energy is nonlinearly transferred back to the plasma through a combination of Landau and cyclotron resonances, resulting in net heating in the parallel direction, preferentially energizing the beam proton population. Crucially, these nonlinear interactions do not drastically alter the morphology of the distribution. This suggests the possibility that the hammerhead may be generated locally within the HCS in the inner heliosphere and subsequently advected outward, where it is eventually measured by PSP. This work lays the ground for future investigations into the kinetic physics of the HCS.
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All authors L. Pezzini, J. L. Verniero, F. Bacchini, A. N. Zhukov, G. Arrò, R. A. Lòpez

Thursday 17 September

Space Physics

Microphysical Diversity in Two Very Closely Spaced Magnetic Switchbacks Observed by Parker Solar Probe

Dipali Vadher, Ankush Bhaskar, Smitha Thampi et al. (+1 more)

Parker Solar Probe observations near the Sun reveal frequent, sudden reversals of the magnetic field known as switchbacks (SBs). Despite their ubiquity, the internal plasma structure and associated heating within SBs remain poorly understood. We present a case study of two closely spaced SBs (referred in text as SB_1 and SB_2) observed on 24 January 2020 using high-cadence magnetic and plasma measurements. Magnetic fluctuations are decomposed into components parallel and perpendicular to the mean field, and their power spectra are analyzed to characterize the turbulent cascade. The Partial Variance of Increments (PVI) method is applied to identify intermittent current-sheet-like features. Both SB intervals exhibit clear Alfvenic behavior and enhanced radial flow; however, their microphysics differ: SB_1 shows a higher proton temperature, larger fluctuation amplitudes, and a denser population of current sheets compared to SB_2. The two events also differ in spectral index, with SB_1 exhibiting a steeper perpendicular slope than SB_2. The elevated intermittency, proton temperature, and transient $\beta > 1$ excursion in SB_1 suggest that localized dissipation at small-scale structures is a plausible driver of the observed heating. These findings demonstrate that SBs are not uniform kinematic deflections but dynamically evolving plasma structures whose internal turbulence may regulate local energy conversion and contribute to the spatially intermittent heating of the near-Sun solar wind.
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All authors Dipali Vadher, Ankush Bhaskar, Smitha Thampi, Kamlesh Pathak

Space Physics · Cross-listed from gr-qc

Gravity from Invariant Weyl-Integrable space-time (IWIST)

José Edgar Madriz Aguilar, A. Bernal, M. Montes et al. (+1 more)

In this paper we propose a geometrically motivated formulation of gravity in an invariant Weyl–Integrable space-time (IWIST), in which the background geometry is not imposed a priori but is dynamically determined through the Palatini variational principle. For a scalar field non-minimally coupled to gravity action, the resulting compatibility condition defines a Weyl–Integrable geometry which is preserved by a local Weyl transformation of the metric and the geo\-me\-tri\-cal scalar field. We construct an action invariant under both diffeomorphisms and Weyl transformations and introduce a Weyl-covariant variational procedure based on an invariant extension of the divergence theorem. The corresponding field equations are obtained for the metric, the Weyl scalar, and the Weyl gauge field. We further formulate the theory in the Einstein–Riemann frame, where the effective metric is Riemannian and the scalar field is re\-inter\-pre\-ted as a phy\-si\-cal degree of freedom of geometric origin. Finally, we propose a geometrical mechanism for the explicit breaking of Weyl symmetry by introducing a coupling between the Weyl gauge field and a current constructed from the scalar sector. The resulting theory remains diffeomorphism covariant while departing from local Weyl invariance. The Einstein–Riemann representation of the broken theory contains an additional generally covariant interaction, making the Weyl-invariant model a particular limit of a more general gravitational theory.
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All authors José Edgar Madriz Aguilar, A. Bernal, M. Montes, J. Zamarripa

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

Widespread plasma jets in the Martian magnetosheath revealed by dual-spacecraft observations

Abigail Tadlock, Chuanfei Dong, Chi Zhang et al. (+4 more)

Plasma jets in planetary magnetosheaths are transient, high dynamic pressure structures capable of strongly perturbing downstream magnetospheres and modulating solar wind energy transfer. Although recently identified at Mars, their formation mechanisms and global occurrence remain poorly constrained. Using dual-spacecraft observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen-1, we show that magnetosheath jets occur throughout the Martian magnetosheath, in striking contrast to Earth where jet occurrence is strongly controlled by interplanetary magnetic field orientation and largely confined to quasi-parallel shock regions. We propose that this widespread distribution is linked to Mars' extended hydrogen corona, which generates pickup ions that drive proton-cyclotron waves upstream of the bow shock. Because this mechanism is generic to any body with an extended corona (or exosphere) embedded in a stellar wind, this finding bears on solar-wind interactions at comets and other small bodies, and on the space environments of unmagnetized terrestrial exoplanets. These results indicate that magnetosheath jet formation can be governed not only by external solar wind forcing but also by intrinsic planetary properties, pointing to a previously unrecognized pathway for solar wind-planet coupling at unmagnetized worlds.
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All authors Abigail Tadlock, Chuanfei Dong, Chi Zhang, Savvas Raptis, Hongyang Zhou, Xinmin Li, Jiawei Gao

Tuesday 15 September

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

Landau Damping Beyond Smooth Velocity Distributions: A Dispersion-Free Lagrangian Time-Domain Framework

Huasheng Xie and Jinsong Zhao

The classic theory of Landau damping requires the velocity distribution function (VDF) to be analytically continued into the complex plane, implicitly requiring analyticity, which imposes constraints far more severe than infinite smoothness. Yet physical plasmas—encountered in discrete simulations, noisy spacecraft measurements, or truncated fusion distributions—are inherently non-analytic. This discrepancy poses a foundational “smoothness paradox”: why does Landau damping robustly persist in systems where the mathematical prerequisite of analyticity is profoundly violated? Here we resolve this paradox by demonstrating that wave-particle interaction is governed by a time-dependent resonance width $\Delta v_\mathrm{res}\sim 1/kt$. Using a dispersion-free Lagrangian time-domain solver, we show that this finite width kinematically coarse-grains microscopic VDF defects at early times, acting as a natural low-pass filter that validates smooth analytical proxies—explaining the observed robustness. However, as $t\to\infty$ the resonance width narrows, inevitably forcing the wave to resolve exact topological non-smoothness. This late-time resolution triggers three distinct breakdowns: VDF truncation arrests the resonant phase transition to yield undamped discrete Van Kampen modes; observational noise induces transient algebraic spikes via linear phase-space aliasing; and step-like gradients drive anomalously violent reactive instability growth. We establish the breakdown timescale $t_b\sim 1/k\delta v$, where $\delta v$ is the characteristic scale of the non-smooth defect, providing a quantitative criterion that redefines the validity boundaries of analytic continuation in kinetic theory.
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Space Physics

Alfvénicity and Proximity to Parallel-Mode Marginal Stability in the Slow Solar Wind

Mani K Chettri, Rupak Mukherjee and Hemam D. Singh

The proton temperature anisotropy in the solar wind is bounded by the thresholds of pressure-anisotropy-driven kinetic instabilities, and the distance at which the plasma settles from these thresholds is thought to be regulated by compressive fluctuations through the fluctuating anisotropy effect. We test whether the level of Alfvénicity is associated with this distance in the slow solar wind. Using five years of Wind/SWE bi-Maxwellian proton measurements (2004–2008), we separate slow-wind intervals into Alfvénic and non-Alfvénic populations on the basis of normalized cross helicity and residual energy. We compare their magnetic compressive fraction and normalized compressive amplitude, and measure their proximity to marginal stability in the plane of parallel proton beta and temperature anisotropy using the maximum growth rate over the scanned parallel wavenumbers, $\gamma_{\parallel,\max}$, from a Vlasov dispersion solver. At low matched parallel beta, the Alfvénic slow wind has lower normalized field-strength fluctuation amplitude and reaches the parallel-mode marginal-stability criterion more often than the non-Alfvénic slow wind. This association is consistent with a weaker fluctuating-anisotropy effect in the Alfvénic slow wind, but does not establish a causal relation.
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Space Physics · Cross-listed from physics.plasm-ph

Strong Nonlinear Alfvén Wave Interactions in a Laboratory Plasma

C. H. K. Chen, S. Dorfman, S. Boldyrev et al. (+6 more)

Alfvén waves and their nonlinear interactions are ubiquitous in space and astrophysical plasmas, and are thought to play important roles in the dynamics of these systems, yet their nature remains to be fully understood. We describe experiments performed on the Large Plasma Device to study the nature of counter- and co-propagating wave interactions relevant to strong Alfvénic turbulence. Both interactions were found to produce a broad spectrum of nonlinear modes as a result of a dominant quadratic nonlinearity. The counter-propagating interaction can be explained through the standard reduced MHD nonlinearity, and the co-propagating interaction can be explained through a recently-proposed model that includes second-order nonlinear terms from Hall MHD that dominate at large imbalance and scale with the ion inertial length. The predictions of the latter model were tested in both the experiment and in 3D hybrid simulations, where the nonlinear mode growth rate and ion inertial scale dependence were found to be consistent. Finally, at the obtained interaction strengths, energy was seen to be transferred to progressively smaller perpendicular scales, consistent with a local cascade, although not a state of fully-developed turbulence. These results reveal and verify the mechanisms occurring in balanced and imbalanced turbulence (as well as other Alfvénic nonlinear processes), and represent an important step towards the generation of controlled Alfvénic turbulence in the laboratory.
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All authors C. H. K. Chen, S. Dorfman, S. Boldyrev, L. Franci, A. Mallet, M. Abler, S. Vincena, S. Greess, T. A. Carter

Thursday 10 September

Space Physics

Low-frequency Intermittency and Structures in the Solar Wind at 1 au

Jiaming Wang, Francesco Pecora, Yan Yang et al. (+1 more)

Intermittency in the solar wind is commonly studied within the inertial and dissipative ranges, where scale-dependent magnetic field distributions become increasingly non-Gaussian toward smaller scales until dissipation becomes important. Conversely, whether Gaussianity is recovered at large scales remains unclear. To address this, we systematically examine magnetic field increment kurtosis over scales from 1 minute to 1 year using more than two decades of in situ observations from NASA's Wind and ACE spacecraft. We find that although kurtosis tends toward Gaussian value of 3 near the correlation scales, it generally remains elevated (super-Gaussian) at larger scales. Kurtosis also varies substantially over time, with pronounced super-Gaussian intervals during high solar activity phases and sporadic sub-Gaussian intervals primarily in the radial component. These results provide evidence for large-scale intermittency in the solar wind, potentially arising from mixing of different solar wind streams and nonstationary driving of solar sources.
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All authors Jiaming Wang, Francesco Pecora, Yan Yang, William H. Matthaeus

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

Continuous Learning of Gravity Field Irregularities Around Small Bodies via Neural Hamiltonian ODEs

Giacomo Acciarini and Dario Izzo

We propose to learn the unknown dynamics in the proximity of a small body directly from tracking data, representing them as a feed-forward neural network embedded in the system Hamiltonian. The equations of motion form a Neural Hamiltonian Ordinary Differential Equation, whose variational equations provide exact training gradients: estimation uses position and velocity arcs at realistic noise levels, without acceleration or potential labels, and a continual learning approach warm-starts the network as new data are acquired. The known part of the Hamiltonian carries whatever is available, from the central term and spin state to the constant-density model of the imaged shape. We assess the method against a normalized spherical harmonics expansion estimated from identical arcs through the same machinery, on scenarios built on the shapes of Itokawa, 67P, Bennu and Eros. The network remains usable inside the Brillouin sphere: it plans ballistic descents at Itokawa to \SI{4.6}{m} median touchdown error from tracking alone, against 5.1–\SI{48.9}{m} for harmonics of degree 4–12, and to \SI{0.9}{m} with the imaged shape as prior, a configuration that also recovers localised density anomalies invisible to any harmonics degree. The two representations are complementary, and we discuss their combined use across the phases of a small-body mission.
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Wednesday 9 September

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

Wave Emission and Absorption in a Near-Sun Proton-Cyclotron Wave Storm

Kristopher G Klein, Daniel Verscharen, Mihailo Martinovic et al. (+5 more)

Quantification of energy transport and dissipation in weakly collisional heliospheric plasmas that are far from local thermodynamic equilibrium is an outstanding scientific problem. A central challenge is determining how non-Maxwellian velocity-space structure affects damping and emission of coherent ion-scale waves, especially compared to simplified analytical models for background plasma velocity distributions. In this work, we study the damping and emission of parallel-propagating proton cyclotron waves for two models of proton velocity distributions measured by the SPAN-I instrument on board Parker Solar Probe during an extended storm of waves with left-hand polarization in the solar wind at a heliocentric distance of 30.1 solar radii. Using the measured velocity distribution rather than a two-component bi-Maxwellian model predicts instabilities consistent with the observed coherent waves. For intervals in which both models predict net damping, the observed VDF model yields weaker damping in 90% of cases, with a reduction in the integrated heating rate of 0.44 relative to the bi-Maxwellian model. These results suggest that simplified analytical velocity distribution models may overestimate cyclotron damping and underestimate wave emission in the near-Sun solar wind.
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All authors Kristopher G Klein, Daniel Verscharen, Mihailo Martinovic, Niranjana, Ali Rahmati, Roberto Livi, Davin Larson, Michael Stevens

Space Physics

Cascade models of anisotropic turbulence in magnetized plasma of solar wind

A. Bershadskii

We present a physical framework for Alfvénic solar wind turbulence in which the plasma is modeled as discrete domains with local rotational symmetry about the domain-mean magnetic field. Using this symmetry, we construct minimalist cascade models governed by two characteristic time scales, nonlinear and Alfvénic, associated, respectively, with the perpendicular and parallel directions relative to the domain-mean magnetic field. Within this partial symmetry, we also characterize the anisotropy of each domain by a single additional geometrical parameter, the alignment angle between the domain-mean velocity and magnetic fields. We introduce a stochastic renewal process with a bimodal waiting-time distribution based on these two time scales, yielding a two-branch renormalization solution for the total energy cascade: a statistically robust branch with an Iroshnikov-Kraichnan-like $k^{-3/2}$ spectrum, and a statistically marginal branch with a Kolmogorov-like $k^{-5/3}$ spectrum. Utilizing principles of causality and cascade stability, we show that the system selects the faster cascade rate between the two available whenever energy-flux fluctuations become supercritical, preventing intermittent flux accumulation. Consequently, during solar wind expansion, balanced domains (with low cross-helicity) undergo a first-order phase transition from the slow $k^{-3/2}$ cascade to the fast $k^{-5/3}$ cascade. The transition is accelerated by heterogeneous nucleation at switchbacks. Incorporating a forward magnetic helicity cascade slaved to the energy cascade, we show that the large-scale spectra decouple into a flat $k^{-3/4}$ magnetic spectrum and a $k^{-3/2}$ kinetic spectrum. Data from Voyager, Ulysses, Helios, Wind, and PSP confirm these spectral signatures across diverse heliospheric regions.
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Space Physics · Cross-listed from astro-ph.SR

On the 3D Magnetic Structure of Coronal Mass Ejections Through the Solar Corona

Erika Palmerio, Michal Ben-Nun, Tibor Török et al. (+2 more)

The magnetic fields that make up the internal structure of coronal mass ejections (CMEs) are thought to be organised in a flux rope configuration, consisting of twisted magnetic fields that wind about a central axis. Remote-sensing observations of CMEs show a wide range of morphologies, dynamics, and evolution, including rotation, non-uniform expansion, deflection, and interaction with the ambient solar wind. In-situ measurements, however, typically consist of a single 1D spacecraft trajectory through a large 3D structure (or few at best), restricting our ability to determine how CME magnetic structure varies in space and time. In this work, we analyse the magnetic configuration of two idealised CMEs during their early evolution in the range 1-30 $R_{\odot}$ using the Magnetohydrodynamic Algorithm Outside a Sphere code. The initial flux ropes differ only in their orientation with respect to the global dipole and erupt from a bipolar active region below the streamer belt in a simplified coronal environment. We deploy a fleet of synthetic spacecraft throughout the CMEs' paths at different combinations of latitudes, longitudes, and heliocentric distances. We identify and examine flux rope signatures in the synthetic in-situ profiles to characterise radial variations as well as latitudinal/longitudinal ones. We find that, even in a simplified CME erupting under solar minimum-like conditions, the sampling location significantly affects the global structure that would be deduced from common flux rope reconstruction and analysis techniques used for in-situ measurements. Additionally, we consider possible in-situ signatures that may serve as indicators of the source region's topology.
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All authors Erika Palmerio, Michal Ben-Nun, Tibor Török, Cooper Downs, Viacheslav S. Titov