7,662 papers in this slice of arXiv.
Katariina Nykyri
The Daniel K. Inouye Solar Telescope (DKIST) has resolved Kelvin--Helmholtz (KH) vortices at photospheric magnetic-flux boundaries with a characteristic wavelength of 65 km. I estimate whether these vortices can supply the photospheric driver for cross-scale plasma heating through reconnection across different heights from photosphere to low-corona. Using the simulated MURaM shear, density contrast, and 500 km vertical extent, together with a representative photospheric density, gives a shear-energy density of 1.35×102
Daegyun Choi, Donghoon Kim, Henzeh Leeghim
In-space servicing has been receiving great attention to extend the operation of spacecraft with defective components. This requires rendezvous and proximity operations for a chaser to provide service to a target. This work constructs a fuzzy inference system-based controller for the chaser to reach the cooperative target on a circular orbit in the final approach phase while minimizing the energy consumption of the chaser. The offline training process performed by a genetic algorithm deals with multiple initial relative positions of the chaser, and the trained controller is validated using a testing environment with disturbances, which differs from the training scenarios.
Immanuel Christopher Jebaraj, Lucas Colomban, Oleksiy Agapitov +7
Diffusive shock acceleration, at shocks from coronal mass ejections to supernova-remnant blast waves, presupposes a scattering wave field that the accelerated particles themselves maintain. This self-regulation has not been resolved in situ. We report Parker Solar Probe observations of a fast (~2800 km/s), near-parallel interplanetary shock at 0.24 AU on 2023 March 13 and separate its upstream wave field into four families, a classification not made before at a fast shock near the Sun. Right-hand and left-hand circularly polarized families over a common wavenumber band, with a field-aligned linearly polarized family, are cyclotron-resonant with the suprathermal-to-MeV protons streaming from the shock: the beam drives the field that scatters it, and the measured mean free path, half the precursor scale, leaves the beam anisotropic enough to sustain the drive. Outside this loop lies a weak, oblique, linearly polarized component, a few per cent of the wave power, resolved here for the first time at an in situ foreshock. Its in-phase density and field-magnitude fluctuations identify the compressive part as fast magnetosonic and shift the cyclotron-resonance energies of the resonant families by up to 13 % along the precursor. Acceleration at shocks inside 0.3 AU is governed upstream, in a foreshock the shock builds for itself.
B. Tripathi, A. E. Fraser, P. W. Terry +3
At every scale they occupy, magnetic fields affect various phenomena, including star formation, cosmic ray transport, charged particle acceleration, space weather, transport in planetary atmospheres, and laboratory plasmas. These fields are often generated and sustained by turbulent flows in a process called the dynamo. In 1955, E. N. Parker parameterized the effects of small-scale turbulence to propose a mean-field dynamo theory. The widely used theory reproduces observed large-scale fields but suffers from difficulty in tuning parameters as they are not justified from first principles: Studies of turbulent flows show tangled magnetic fields, which are folded and fragmented into small-scale structures due to shear-flow straining. Here, considering a shear flow that is unstable and driven, we develop analytic theory and perform three-dimensional (3D), advanced computer simulations of turbulence with up to 4096 x 4096 x 8192 grid points, showing ab initio generation of quasi-periodic, large-scale magnetic fields. The generation occurs via the mean-vorticity effect---an additional mean-field dynamo process postulated in 1990. Crucial to this dynamo is the prior generation of large-scale 3D jets, robustly produced as topologically protected and exact nonlinear solutions of the magnetohydrodynamic equations. The jet-driven dynamo applies to shear-driven laboratory and astrophysical systems. These include binary neutron star mergers, where the reported dynamo likely operates on microsecond timescales to produce in milliseconds some of the strongest magnetic fields in the Universe, providing signals for multimessenger astronomy.
Yanwen Wang, Rohit Chhiber, Arcadi V. Usmanov +2
The solar wind is an outflow of solar plasma that expands from the corona to fill the heliosphere. Its turbulence provides a pathway for non-adiabatic heating and acceleration, and is therefore central to understanding the thermodynamic and magnetohydrodynamic (MHD) evolution of the young solar wind. However, the variation of its turbulence properties over the solar activity cycle and the connection of these properties to solar source regions remains incompletely understood. Here we analyze observations from 25 solar orbits of NASA's Parker Solar Probe (PSP) mission, in combination with a global MHD model, photospheric magnetograms, and extreme ultraviolet maps of the low corona, to investigate the solar-cycle dependence and the solar sources of turbulence in the very inner heliosphere. The observations reveal pronounced solar-activity variation in fluctuation amplitude, cross helicity, and related turbulence properties. By tracing PSP-connected magnetic flux tubes to their solar sources, we demonstrate that high turbulent-energy intervals are preferentially connected to coronal-hole sources with unipolar magnetic topology, whereas low turbulent-energy intervals are associated with multipolar topology and active-region environments. Our study combines in-situ measurements with numerical modeling and remote sensing observations to reveal how solar-cycle-dependent source structure determines turbulence variability and plasma heating in the young solar wind.
Joaquin G. Lopez-Cepero, Rafael Vazquez, Julio C. Sanchez
This work presents the design of a Linear Quadratic Regulator for relative motion control near periodic orbits in the Circular Restricted Three-Body Problem (CR3BP), formulated in non-singular toroidal coordinates. The key result exploits the rotational quasi-periodicity of the toroidal coordinate transformation. A uniqueness argument on the stabilizing solution of the associated difference Riccati equation proves the optimal control gains need only be computed for a single orbital period. The controller is validated against the full non-linear CR3BP dynamics on an L1 Northern halo orbit in the Earth-Moon system, and further against a high-fidelity ephemeris model, demonstrating successful reconfiguration maneuvers on the invariant torus with low control effort. Compared with an impulsive targeting and station-keeping baseline, the proposed controller attains a comparable tracking accuracy while reducing the total control effort by approximately 40%.
Minhaj Uddin Ahmad, Sagar Dasgupta, Muhammad Sami Irfan +3
State departments of transportation (DOTs) in the United States increasingly rely on statewide continuously operating reference station (CORS) networks to support high-precision Global Navigation Satellite System (GNSS)-based positioning and timing for intelligent transportation systems. These networks also provide continuous observations that can support regional GNSS integrity monitoring. This study develops and demonstrates a framework that treats a statewide CORS network as a spatially distributed sensor system for identifying unintentional (environmental) and intentional (cyber) interference when GNSS measurements deviate from expected spatial patterns. We develop a graph-based Network Consistency Framework (NCF) that evaluates each station against its spatial neighborhood using four metrics: neighborhood residual, spatial gradient, residual, and graph smoothness. These metrics are combined into a Network Consistency Index (NCI). The framework is demonstrated using two consecutive days of four-constellation observations from 50 stations in the Alabama DOT-maintained CORS network, using changes in vertical total electron content (ΔVTEC) and the Rate of TEC Index (ROTI) as spatially coherent observables. The framework quantified network-wide spatial consistency and identified localized anomalies. Detected anomalies indicate stations whose observations deviated from the surrounding regional network, signaling potential integrity issues. Determining whether anomalies result from receiver faults, localized interference, spoofing, or other causes requires further investigation. This study introduces statewide CORS networks as regional GNSS integrity observatories and presents the NCF and NCI for graph-based spatial integrity monitoring. Transportation agencies can implement the framework using existing CORS observations to monitor network integrity and identify localized anomalies.
H. J. Austin, N. P. Savani
Coronal mass ejections (CMEs) from the Sun can have severe impacts on the Earth environment in the form of geomagnetic storms. These storms pose a risk to the global technological infrastructure, making the prediction of these events imperative. In this paper, we have broadened the statistical verification of the Bz4Cast tool, the first empirically-driven model to forecast solar wind magnetic vectors inside a CME prior to their Earth arrival. Twenty five CME events (between 2012 and 2016) have been tested with the Bz4Cast model, and the skills have been compared to the heuristic approach of NOAA's Space Weather Prediction Center (SWPC) G-scale for 3-day geomagnetic storm forecasts. For a broad range of scores, and within uncertainty, the Bz4Cast architecture provided the same skill as the experienced on-duty forecasters at SWPC. The most prominent difference is that the Bz4Cast architecture provides a slightly higher false alarm ratio than the SWPC 3-day forecast.
Ian M. DesJardin, Christopher Bard, Natalia Y. Buzulukova +1
The equations of reduced magnetohydrodynamics (RMHD) isolate the Alfvénic energy transfer and turbulence dynamics from MHD in a computationally tractable way. In this study, we derive the equations of RMHD for a low β plasma in a dipole coordinate system aligned with the background magnetic field using a multiscale analysis. The Kreiss theorem is used to derive the equilibrium conditions that the background conditions must satisfy on the time scale of MHD turbulence. From these, we find a connection between plasma flow along flux tubes and changes in the Alfvén speed that may drive nonlinear wave effects. The final equations demonstrate an intimate coupling between field aligned currents and plasma vorticity including the effects of nonuniform flux tube area and realistic plasma density profiles. This work has immediate application to the magnetosphere-ionosphere coupling problem in the Earth's magnetosphere as it provides a way to link dynamically evolving field aligned currents from the magnetosphere, especially important during geomagnetic storms and substorms, with the development of magnetohydrodynamic turbulence at low altitudes in a self-consistent manner. This also clarifies the role of Alfvén waves as a transfer mechanism of energy under these inhomogeneous circumstances while remaining simple enough to make predictions. Furthermore, this study makes use of a novel methodology, a computer algebra system, in performing the brunt of algebraic work under complicated coordinate systems. We hope this approach serves as a template for performing reproducible and verifiable multiscale perturbation analysis under arbitrarily complex geometries.
Chi Zhang, Chuanfei Dong, Gangkai Poh +11
Atmospheric ion escape driven by the solar wind is a key process controlling the long-term loss of the Martian atmosphere. Localized plasma clouds can carry substantial fluxes of planetary ions away from Mars, representing episodes of bulk escape. However, their origin has remained unclear due to the absence of simultaneous upstream measurements. Using joint observations from the MAVEN and Tianwen-1 missions, which provide real-time upstream monitoring, we present direct evidence that these plasma clouds are nonlinear wave packets generated by the Kelvin-Helmholtz instability (KHI). The spatial scale of KH waves is constrained for the first time via two-point measurements. Ion fluxes within plasma clouds are one to two orders of magnitude higher than those in typical steady-state escape channels. Our results indicate that KHI is an important process for solar wind coupling to planetary upper atmospheres and plays a crucial role in shaping atmospheric ion escape for unmagnetized planets.
Keshav Aggarwal, R. K. Choudhary, Abhirup Datta +4
Irregularities in electron density within the interplanetary medium (IPM) can cause fluctuations in the Doppler frequency of spacecraft radio signals. The amplitude of these fluctuations depends on factors such as the carrier frequency, propagation geometry, and link configuration. However, quantitative characterization of these effects across different frequencies in various occultation experiments is currently limited. We analyze five complementary datasets: two-way S-band observations from Chandrayaan-3 outside the lunar ionosphere, two-way S-band data from Chandrayaan-2 during lunar occultation, one-way S/X band measurements from the Venus Express Radio Science (VeRa)/Akatsuki Radio Science (Akatsuki) under IPM-only conditions, and one-way X-band Akatsuki data during solar occultation. The Chandrayaan-3 and Akatsuki IPM observations isolate IPM effects by excluding contributions from planetary atmospheres, the lunar ionosphere, and, except during solar occultation, the solar corona. Chandrayaan-3 data sample dynamically evolving Earth-Moon geometries and exhibit weak, mHz-level Doppler fluctuations, while Chandrayaan-2 observations provide near-lunar plasma benchmarks with higher amplitudes, during quiet time solar and geomagnetic conditions. Akatsuki and VeRa's IPM-only measurements capture long-path interplanetary effects, whereas Akatsuki solar occultation data reveal strong coronal signatures. Power spectral density analysis indicates Kolmogorov-like turbulence for lunar occultation and solar occultation cases, while IPM-only spectra show low-amplitude fluctuations. These results quantify the IPM contribution to Doppler noise, demonstrate the enhanced plasma sensitivity of two-way coherent links, and provide constraints relevant to turbulence modelling, precision spacecraft tracking, and the interpretation of radio occultation experiments.
Trevor P. Erwin, Brandon C. Johnson, David Minton +1
Impact-generated crater rays are well-documented on the Moon, with most appearing as high-albedo streaks extending radially from a crater's center. On Mars, however, crater rays are significantly rarer and discernible only through thermal imaging due to their lower thermal inertia compared to surrounding terrain. This study presents the first comparative analysis between the lengths of Martian and lunar crater rays, including lunar albedo rays and cold spots, which are ray-like thermal anomalies associated with many of the youngest lunar craters. Our findings indicate that both Martian crater rays and lunar cold spots extend significantly farther than lunar albedo rays, with lengths an order of magnitude greater for craters of equivalent diameter. Furthermore, we propose a connection between the formation mechanisms of Martian crater rays and lunar cold spots based on their thermal properties. By integrating thermal rays into existing ejecta models, we refine the understanding of crater-ray formation and suggest that Martian crater rays and lunar cold spots may share a similar formation mechanism via secondary cratering processes. Advancing knowledge of these features has implications for impact dynamics and surface evolution across planetary bodies.
Yogesh, Aparupa Apsara Baruah, Dibyendu Chakrabarty +3
Understanding the spatial coherence of solar wind plasma and magnetic field properties is essential for interpreting multi-spacecraft observations and for characterizing the large-scale structure of heliospheric transients. In this study, we quantify the spatial correlation of six key solar wind parameters - interplanetary magnetic field components, bulk flow speed, proton number density, and the alpha-to-proton abundance ratio - using simultaneous measurements from the ACE and Wind spacecraft as a function of their instantaneous separation distance. The analysis is performed separately for intervals of background solar wind, Interplanetary Coronal Mass Ejections (ICMEs), and Stream Interaction Regions (SIRs). The decay of the Pearson correlation coefficient with distance is modeled using an exponential function to infer characteristic de-correlation length scales. We find that the bulk solar wind speed is the most spatially coherent parameter in all regimes, while plasma composition exhibits the weakest coherence. Magnetic field coherence shows strong dependence on solar wind structure: ICMEs display near-unity correlations and the largest magnetic coherence scales, consistent with organized, flux-rope-like configurations, whereas SIRs exhibit reduced coherence - particularly in the north - south magnetic field component - reflecting compressed and turbulent plasma. The background solar wind exhibits intermediate behavior, with large-scale coherence in bulk plasma properties but shorter coherence lengths in magnetic fluctuations. These results provide a quantitative framework for distinguishing solar wind structures based on their spatial coherence properties and have important implications for multi-point solar wind studies and space weather applications.
Julia van Ravenswaaij, Ines Wilms, Ivan Ricardo +1
Early detection of major solar flares is critical for defense operations due to their potential to disturb radar and radio systems. Typically, soft X-ray flux is used to monitor and classify solar flares, but since this flux has to be measured in space, it means that its availability itself is dependent on space weather conditions. For this reason, in this paper, we investigated the feasibility of using ground radio observations to monitor major (M5+ class) solar flares. We made use of datasets from the GOES-16 satellite and the Radio Solar Telescope Network in the time range between March 2023 and March 2025. An elastic net regularized logistic regression model was trained on this data, optimized through a grid search and with incorporated class weighting for class imbalance. It was found that especially higher frequencies (8800 MHz) had a reasonable ability in monitoring and predicting major flares (precision and recall for flare events are 53% and 65%, respectively - implying that roughly one third of flares were not detected - with signals appearing, on average, 3 to 4 minutes before the M5 threshold is exceeded). Radio measurements at super high frequencies can thus serve as an alternative method to monitor major solar flaring activity.
Radoslav Bucik, Raul Gomez-Herrero, Samuel T. Hart +2
We analyze an impulsive solar energetic particle (SEP) event observed by Solar Orbiter at 0.93 au on 2022 December 24 that exhibits a pronounced intensity dropout between approximately 07:15 and 10:00 UT. Pitch-angle distributions show a near-field-aligned beam before the dropout, which disappears abruptly at the dropout onset. At the same time, a weak 100--200 keV component appears at pitch angles of about 90--180 degrees; no comparable enhancement over this pitch-angle range is present at MeV energies. The dropout onset is not accompanied by an abrupt change in the in situ magnetic field or solar wind plasma. Solar imaging associates the SEP event with a jet from a compact source. Ballistic back mapping, together with Potential Field Source Surface extrapolations and quasi-separatrix-layer proxy diagnostics, indicates that Solar Orbiter nominally connects to the source region, but lies close to strong connectivity gradients where small displacement may shift the connection to neighboring open field lines. The in situ measurements show that the event occurs during a magnetic-cloud passage and that additional dropouts occur later in the event. These results favor an interpretation in which the dropout reflects rapid changes in particle access between adjacent flux tubes, while the magnetic cloud may help preserve the sharp SEP intensity gradients between them.
Ruochen Wang, Xiaoli Bai
Thermospheric mass density governs aerodynamic drag in low Earth orbit and is a primary source of uncertainty in orbit prediction and conjunction assessment, particularly during geomagnetic disturbances. We present AETHER-P3 (Accelerometer-driven Estimation of THERmospheric density-A Physics-Informed Probabilistic Prediction Platform), a machine-learning-based global thermospheric density forecasting model that provides multi-step forecasts up to 6 hr ahead using a 3-hr input window, with predictive uncertainty estimates. AETHER-P3 formulates thermospheric density forecasting as a sequence-to-sequence regression task conditioned on recent space weather evolution and a user-specified sequence of future times and locations. To enhance physical consistency and generalization, AETHER-P3 incorporates JB2008 and NRLMSISE-00 density estimates evaluated at future locations, along with solar, geomagnetic, and solar-wind drivers. The network employs dual recurrent encoders and an evidential Normal-Gamma output head to jointly estimate forecast mean and uncertainty. The model is evaluated using independent satellite test cases spanning quiet, moderate, and extreme geomagnetic conditions. During quiet periods, AETHER-P3 achieves high forecast skill (R=0.95). Under moderate activity, strong skill is retained (R=0.93), with reduced physical-domain errors than empirical baseline models. During extreme storm conditions, deterministic forecast skill degrades as expected yet remains robust (R=0.89-0.90). Predictive uncertainty remains well calibrated across all regimes. These results establish AETHER-P3 as a practical, low-latency, uncertainty-aware capability for thermospheric density forecasting that supports orbit prediction, drag-risk assessment, and operational decision-making over its validated altitude range of approximately 300-520 km, with highest confidence in the data-rich 400-520 km region.
Yuri A. Omelchenko, Igor V. Sokolov, Lulu Zhao +1
We present a novel efficient technique for hybrid (kinetic ions, quasi-neutral fluid electrons) simulations of non-relativistic magnetized collisionless plasma shocks, frequently observed near the Sun, in the solar system, and beyond. This Adaptive Frame-Of-Reference Algorithm (AFORA) enables multi-dimensional simulations of plasma shocks along with concomitant ion acceleration in the shock frame, where shock evolution remains quasi-steady. Compared to moving shocks, this technique allows us to reduce the simulation time and domain size to a minimum while achieving converged shock dynamics and spectra of energetic ions. Using an event-driven (asynchronous) hybrid code, HYPERS, we demonstrate this approach in two spatial dimensions for different orientations of the background magnetic field with respect to the shock normal. Our results show excellent agreement of simulation shocks with observations of interplanetary (IP) shocks. We verify that different shock configurations (quasi-parallel, oblique, and quasi-perpendicular) convert bulk plasma flow energy into ion acceleration with varying degrees of efficiency. These findings underscore the importance of efficient and robust numerical algorithms for future high-resolution modeling of plasma shocks and ion acceleration in three dimensions. In addition to enabling efficient computational studies of collisionless shocks in general, this work paves the way for accurate prediction of seed populations of Solar Energetic Particles (SEPs), generated by coronal mass ejection (CME) shocks. The characteristics of seed ions can be used as inputs to Fokker-Planck models that simulate long-term transport and acceleration of ions along magnetic field lines through their interactions with background solar wind turbulence.
Deep Ghuge, Daniel J. Gershman, Vadim Uritsky +1
We present a morphology-first framework for narrowing the search for magnetic-reconnection candidates in Magnetospheric Multiscale (MMS) burst-mode data. The target is the small, short, and frequently electron-only reconnecting current sheets that occur in turbulent magnetosheath plasma. The pipeline operates in two stages. A local frame-quality gate based on minimum-variance analysis first retains only windows whose current-sheet coordinates are well defined. A one-class Deep Support Vector Data Description neural network then scores those windows against a library of 3,000 physically calibrated synthetic current sheets generated by Monte Carlo from a single published reference event. Acceptance into the surrogate library is governed by the second-order structure function S2(τ): a candidate is admitted only if its multi-scale fingerprint tracks that of the seed event inside a tolerance band, together with a small number of shape-based checks. This S2(τ)-anchored construction defines the in-class distribution directly from a well-understood reference event and sidesteps the absence of a curated negative class in turbulent magnetosheath data. Applied to 15 magnetosheath turbulence intervals from the literature (1.58 h of burst-mode coverage), the framework compresses 22,775 sliding windows to 270 candidate detections (a 98.8% reduction). Manual visual screening identifies 93 of these as candidate reconnection events and a further 118 as sheet-like, retaining 78% of the queue for follow-up; the candidate-reconnection pool extends well beyond the 22 detections that overlap the published reconnection-event catalog used here as a sanity check. The framework is intended as the data-reduction stage of a broader reconnection-search workflow, offered here as an initial proof of concept before extending the one-class design to additional feature channels.
Giovanni Lombardi, Riccardo Di Spirito, Sergio Fabiani +48
The CUbesat Solar Polarimeter (CUSP) mission aims to measure the linear polarization of solar flares in the hard X-ray band by means of a Compton scattering polarimeter. CUSP is a project in the framework of the Alcor Program of the Italian Space Agency aimed at developing new CubeSat missions. We present the outcomes of the CUSP's Phase B study, which is ended on 2 July 2026. The design solutions adopted for the mission's most critical multi-physics design drivers will be discussed, these solutions have been formulated and applied to demonstrate compliance with system requirements at both the spacecraft and platform levels. Moreover, we will discuss the validation of the Payload model based on the environmental testing campaign (e.g., vibration) carried out on a demonstrator.
Joshua Goodwill, Subash Adhikari, Francesco Pecora +10
Averaging techniques in solar wind measurements have been a longstanding subject of debate. Using Parker Solar Probe (PSP) observations from encounters 1 to 19, we investigate how averaging timescales influence the characterization of turbulent properties across the Alfvenic transition. We compute the rolling mean Alfven Mach number over various averaging intervals, which are then analyzed against switchbacks, magnetic fluctuation energy, and correlation time. We find that the distribution of subAlfvenic intervals is relatively insensitive to judiciously-chosen averaging scales. In contrast, magnetic fluctuation energies increase systematically with larger averaging window, while maintaining a consistent profile across the Alfven transition. We further show that the effective magnetic correlation time decreases with decreasing heliocentric distance and MA, reaching values of several minutes approaching MA =1. These results demonstrate the importance of choosing physically meaningful backgrounds for turbulence parameters, such as the correlation scales, and their impacts on characterizing the solar wind.