Magnetic Reconnection Energy Fluxes in the Near-Sun Heliospheric Current Sheet as Observed by Parker Solar Probe

Context. All particle-in-cell (PIC) simulations of the pulsar magnetosphere over the past decade show closed line regions that end a significant distance inside the light cylinder, and manifest thick, strongly dissipative separatrix surfaces instead of thin current sheets, with a tip that has a distinct pointed Y shape rather than a T shape. Aims. We need to understand the origin of these results, which were not predicted by our earlier numerical simulations of the pulsar magnetosphere. To gain new insight into this problem, we set out to obtain the theoretical steady-state solution of the ideal 3D force-free magnetosphere with zero dissipation along the separatrix and equatorial current sheets. To achieve this goal, we developed a novel numerical method. Methods. We solved two independent magnetospheric problems without current sheet discontinuities in the domains of open and closed field lines and adjusted the shape of their interface (the separatrix) to satisfy the pressure balance between the two regions. We obtained the solution using meshless physics-informed neural networks (PINNs). Results. We present our first results for an inclined dipole rotator using the new methodology. We are able to zoom-in around the Y-point and inside the closed line region, and we observe new interesting features. This is the first time the steady-state 3D problem is addressed directly, rather than through a time-dependent simulation that eventually relaxes to a steady state. Conclusions. We trained a neural network that instantaneously yields the three components of the magnetic field and their spatial derivatives at any given point. Our results demonstrate the potential of the new method to generate new solutions of the ideal pulsar magnetosphere.

Solar energetic particle transport via the heliospheric current sheet: Evidence of a ground-level response on All Saints Day, 2014

Abstract Quasi-separatrix layers (QSLs) at the Sun are created in regions where channels of open magnetic flux have footpoints near regions of large-scale closed magnetic flux. These regions show rapid changes in curvature and field strength. Numerical simulations of a relaxed coronal magnetic field and solar wind using the Magnetohydrodynamic Algorithm outside a Sphere model coupled to the Energetic Particle Radiation Environment Module model indicate common sources of energetic particles over broad longitudinal distributions in the background solar wind. These regions accelerate energetic particles from QSLs and current sheets. Here, we develop an analytical framework to describe the acceleration of energetic particles due to the magnetic field changes within and near separatrix layers. The reduced field strength near the separatrix layer drives magnetic field magnitude changes that accelerate energetic particles in the presence of plasma flow along the structure. Separatrix layers are prone to magnetic reconnection, creating fluctuations in the field that propagate out from the Sun, and release material previously contained within closed magnetic field structures, which are often rich in heavy ions and 3 He ions. Thus, we present a model of energetic particles accelerated from separatrix layers in the corona. Our results provide a plausible source for seed populations near the Sun.

Abstract We perform a comprehensive superposed epoch analysis of more than 200 corotating interaction regions (CIRs) using WIND spacecraft observations at 1 au. The stream interfaces are identified by minimum variance analysis, and turbulence properties are evaluated using wavelet transforms over a wide range of temporal scales. The analysis of normalized cross helicity ( σ c ) and normalized residual energy ( σ r ) reveals distinct turbulence behaviors across frequencies. The spectral indices of both magnetic and velocity fluctuations smoothly transition from steeper in the slow wind to shallower in the fast wind, while a localized steepening of the velocity spectra near the interface indicates enhanced dissipation due to compression. Across broad frequency bands, σ c shows a clear dip at the stream interface—signifying increased inward Alfvén wave energy—whereas σ r displays a peak–valley–peak structure mainly driven by large-scale velocity shear. In lower-frequency ranges, velocity shear artificially enhances velocity fluctuation energy, producing strong peaks in σ r , while higher-frequency ranges show a smooth increase of σ r from slow wind to fast wind. Nearly half of the analyzed CIRs are accompanied by a heliospheric current sheet (HCS), with many HCSs closely aligned with the stream interface, suggesting an intrinsic link between the two structures. Our findings offer valuable clues for reconciling discrepancies among earlier observational and simulation studies, and provide new insight into how compression and velocity shear modulate solar wind turbulence near CIRs.

We study Jupiter’s DAM radio storms to identify the features that may correlate with solar wind and coronal mass ejections (CME). We investigate the dynamics of DAM storms and burst features, and explain them by considering MHD processes associated with Io and the presence of gas in Jupiter’s lower magnetosphere. DAM radio storms occur when plasma injected by Io or by solar wind propagating along Jupiter's magnetic field lines into the auroral zone of Jupiter’s lower magnetosphere together with low-frequency Alfvén wave. Those MHD oscillations in low magnetosphere can trigger ionization processes and create streamers, activating maser instabilities in the electron plasma. This can occur under the influence of dense solar wind and CME that penetrate to Jupiter's magnetosphere, creating high-latitude currents with non-Io radio storms, and enhancing Io-dependent sources of DAM radio emissions. We found that dynamics of development of Io-dependent and non-Io DAM radio storms have similar features and evolutionary peculiarities. That time periodicities (5 min and 20 min durations) may connected with MHD instabilities activated by Io, that modulate the current sheets system in all auroral zone. The power of Io-dependent storms is modulated by the solar wind pressure on the magnetosphere of Jupiter. On the other hand, in non-Io radio sources associated with solar plasma injections, due to the content of high-energy ions which scatter on the gas fluids, a number of specific radio bursts are formed, for example, having zebra structures on high-resolution dynamic spectra.

The formation mechanism for the dynamic type II spicules has remained elusive for many years. Their dynamical behaviour has long been linked to magnetic reconnection, yet no conclusive evidence has been provided. However, one recent observational study found signs of magnetic reconnection, as traced by Ellerman bombs (EBs), at the footpoints of many spicules. The triggering of EBs is generally linked to magnetic reconnection due to flux emergence and convective motions in the photosphere. We aim to explore whether we can connect EBs to type II spicules, and determine to what extent we can use EBs as an observational proxy to probe magnetic reconnection in this dynamic. We also aim to provide further insight into the mechanisms that trigger EBs. We used a simulation run with the radiative magnetohydrodynamics code Bifrost to track spicules and study the physical processes underlying their formation. To detect EBs and classify the spicules, we synthesised the chromospheric ̋a spectral line using the multilevel radiative transfer code RH1.5D. We also traced shocks and current sheets to decipher the origin of EBs and spicules. We selected one type II spicule with a strong EB near its footpoint and studied their formation in detail. A magnetoacoustic shock advects the magnetic field lines towards an oppositely directed ambient field, creating a current sheet. The current sheet accelerates dense plasma via a whiplash effect generated by magnetic reconnection into the inclined ambient field, launching the spicule. Several EB profiles trace shock- and magnetic-reconnection-induced dynamics during this process at the spicule footpoint. We present a new EB triggering mechanism in which a shock-induced current sheet reconnects, triggering an EB in the lower solar atmosphere. The shock-induced current sheet generates the upwards propagation of a type II spicule via reconnection outflows. These results provide a plausible physical origin for the recently observed connection between EBs and spicules.

Abstract Fast γ -ray variability in blazars remains a central puzzle in high-energy astrophysics, challenging standard shock acceleration models. Blazars, a subclass of active galactic nuclei with jets pointed close to our line of sight, offer a unique view into jet dynamics. Blazar γ -ray light curves exhibit rapid, high-amplitude flares that point to promising alternative dissipation mechanisms such as magnetic reconnection. This study uses three-dimensional relativistic magnetohydrodynamic (RMHD) and resistive relativistic magnetohydrodynamic (ResRMHD) simulations with the PLUTO code to explore magnetic reconnection in turbulent, magnetized plasma columns. Focusing on current-driven kink instabilities, we identify the formation of current sheets due to magnetic reconnection, leading to plasmoid formation. We develop a novel technique combining hierarchical structure analysis and reconnection diagnostics to identify reconnecting current sheets. A statistical analysis of their geometry and orientation reveals a smaller subset that aligns closely with the jet axis, consistent with the jet-in-jet model. These structures can generate relativistically moving plasmoids with significant Doppler boosting, offering a plausible mechanism for the fast flares superimposed on slowly varying blazar light curves. These findings provide new insights into the plasma dynamics of relativistic jets and strengthen the case for magnetic reconnection as a key mechanism in blazar γ -ray variability.

Abstract Magnetic reconnection in current layers that form intermittently in radiatively inefficient accretion flows onto black holes is a promising mechanism for particle acceleration and high-energy emission. It has been recently proposed that such layers, arising during flux eruption events, can power the rapid TeV flares observed from the core of M87. In this scenario, inverse-Compton scattering of soft radiation from the accretion flow by energetic electron–positron pairs produced near the reconnection layer was suggested as the primary emission mechanism. However, detailed calculations show that radiation from pairs alone cannot account for the GeV emission detected by the Fermi observatory. In this work, we combine analytic estimates with 3D radiative particle-in-cell simulations of pair–proton plasmas to show that the GeV emission can be naturally explained by synchrotron radiation from protons accelerated in the current sheet. Although the exact proton content of the layer is uncertain, our model remains robust across a broad range of proton-to-pair number density ratios. While protons are subdominant in number compared to pairs, our simulations demonstrate that they can be accelerated more efficiently, leading to a self-regulated steady state in which protons dominate the energy budget. Ultimately, proton synchrotron emission accounts for approximately 5%–20% of the total dissipation power. The majority is radiated as MeV photons via pair synchrotron emission, with a smaller fraction emitted as TeV photons through inverse-Compton scattering.

Abstract Magnetic reconnection in a flare current sheet is widely believed to be the main energy release process powering solar flares and coronal mass ejections (CMEs). Modeling this process and determining the channels for the energy release, mass motions, and heating has long been a major goal in space science. We present results from a two-fluid magnetohydrodynamic simulation of an eruptive flare/CME using a newly developed version of the Space Weather Modeling Framework that incorporates two major advances in numerical capability. First, we use the STatistical InjecTion of Condensed Helicity formalism for the energy buildup, so that we start with a potential-field minimum-energy state and slowly form a sheared filament channel over a polarity inversion line as is observed on the Sun. Second, we use a new formulation of the plasma energetics that is explicitly energy conserving while calculating separate electron and ion temperatures and separate parallel and perpendicular pressures, as desired. For this first simulation with our new model, we opted for the nonadiabatic heating to go solely into the protons and for an isotropic pressure. We discuss the resulting energetics of the reconnection and, in particular, the plasma heating in the reconnecting current sheets, mass acceleration, and shock formation. We also discuss the implications of our results for flare/CME observations and for understanding solar eruptions in general.

Abstract The genesis of solar wind remains elusive due to limited multi-instrument observations of its source regions. Here, we introduce a novel “see and touch” technique, integrating remote-sensing observations with in situ measurements from Parker Solar Probe (PSP). This approach allows us to obtain 3D trajectories of flow structures such as streamer blobs and explore their in situ properties. With this approach, we link blobs observed by remote sensing and high-density jets (HDJs) measured in situ. The blobs are embedded in streamer rays, while the HDJs are found when PSP crosses the heliospheric current sheet (HCS). Our findings suggest that large-scale blobs/HDJs originate from primary reconnection in the near-Sun HCS, while secondary reconnection in smaller-scale current sheets forms multiple flux ropes, which merge to trigger further small-scale reconnection. Detailed in situ analysis reveals that turbulent magnetic reconnection is a key mechanism for dissipating filamentary HCS and energizing plasmas in blobs/HDJs. The multiscale magnetic reconnection accelerates the proton core population and mixes it with the beam population, driving bulk acceleration and heating of the nascent slow solar wind.

Abstract Many transients believed to originate from magnetars are thought to be triggered by crustal activity, which feeds back on the surrounding magnetosphere. These perturbations, through a variety of proposed mechanisms, can convert a fraction of the magnetic energy stored in the magnetosphere, as well as the energy injected by crustal activity itself into electromagnetic emission, including X-ray bursts and fast radio bursts. We here provide a first glimpse of this process by coupling magnetoelastic dynamics simulations of the crust to fully three-dimensional relativistic resistive force-free electrodynamic simulations of the magnetosphere. Our simulations demonstrate that the elastodynamical motions of the surface launch a series of fast magnetosonic and Alfvén waves into the magnetosphere. These waves rapidly enter a nonlinear regime, ultimately giving rise to a wide range of phenomena, including monster shock formation, relativistic blast waves, trapped Alfvén waves, nonlinear Alfvén wave ejecta, and transient equatorial current sheets interacting with these waves. After the initial nonlinear phase, the magnetosphere is partially combed out, resembling a strongly perturbed split monopole configuration. Our results can offer hints and potential constraints on fast radio burst emission mechanisms, in particular for hyperactive repeating sources, by placing tight bounds on energy conversion efficiency and possible quasiperiodic imprints on magnetospheric waves by elastic oscillations of the crust.

Abstract While relativistic magnetic reconnection in pair plasmas has emerged in recent years as a candidate for the origin of radiation from extreme astrophysical environments, the corresponding subrelativistic pair-plasma regime has remained less explored, leaving open the question of how relativistic physics affects reconnection. In this paper, we investigate the differences between these regimes by contrasting two-dimensional particle-in-cell simulations of reconnection in pair plasmas with relativistic magnetization ( σ ≫ 1) and subrelativistic magnetization ( σ < 1). By utilizing unprecedentedly large domain sizes and outflow boundary conditions, we demonstrate that lowering the magnetization results in a change in the reconnection geometry from a plasmoid chain to a Petschek geometry, where laminar exhausts bounded by slow-mode shocks emanate from a single diffusion region. We attribute this change to the reduced plasmoid production rate in the low- σ case: When the secondary tearing rate is sufficiently low, plasmoids are too few in number to prevent the system from relaxing into a stable Petschek configuration. This geometric change also affects particle energization: We show that while high- σ plasmoid chains generate power-law energy spectra, low- σ Petschek exhausts merely heat incoming plasma and yield negligible nonthermal acceleration. These results have implications for predicting the global current sheet geometry and the resulting energy spectra in a variety of systems.

We present observations from the International Ultraviolet Explorer (IUE) covering the period from 1981 to 1992 of the long-period single-lined RS Canum Venaticorum (RS CVn) binary star, IM Pegasi, to elucidate the spectral behavior and physical conditions within its atmosphere. The ultraviolet observations reveal signs of flare activity occurring in the chromosphere and transition region of the primary star. In addition to the flaring activity, the emission lines exhibit a spectrum of variations categorized as high, intermediate, and low. The relation between line fluxes and orbital phases has been established. The flaring activity was notably observed in 1985. The reddening of IM Pegasi was assessed using the 2200 Å absorption feature, yielding an estimate of E (B-V) = 0. The average mass loss rate is calculated to be approximately 1.2 × 10− 10 M{_ odot } yr− 1, while the average temperature of the emitting region, determined through Planck’s equation, is approximately 9.2 × 104 K. The energy associated with the flare is estimated to be around 5.6 × 1039 erg, and the average ultraviolet luminosity is approximately 1.23 × 1030 erg s− 1. We attribute the observed spectral variations to a cyclic behavior of the underlying magnetic field, and the flaring activity can be interpreted through the current sheet model.

ABSTRACT A large part of the hot corona consists of magnetically confined, bright plasma loops. These observed loops are in turn structured into bright strands. We investigate the relationship between magnetic field geometry, plasma properties, and bright strands with the help of a three-dimensional resistive magnetohydrodynamic (MHD) simulation of a coronal loop rooted in a self-consistent convection zone layer. We find that it is impossible to identify a loop as a simple coherent magnetic flux tube that coincides with plasma of nearly uniform temperature and density. The location of bright structures is determined by a complex interplay between heating, cooling, and evaporation time-scales. Current sheets form preferentially at the interfaces of magnetic flux from different sources. They may also form within bundles of magnetic field lines since motions within magnetic concentrations drive plasma flows on a range of time-scales that provide further sub-structure and can locally enhance magnetic field gradients and thus facilitate magnetic reconnection. The numerical experiment therefore possesses aspects of both the flux tube tectonics and flux braiding models. While modelling an observed coronal loop as a cylindrical flux tube is useful to understand the physics of specific heating mechanisms in isolation, it does not describe well the structure of a coronal loop rooted in a self-consistently evolving convection zone.

A key open question in astrophysics is how plasma is transported within strongly magnetized, rapidly rotating systems. Magnetic reconnection and flux tube interchange are possible mechanisms, with Jupiter serving as the best local analog for distant systems. However, magnetic reconnection at Jupiter remains poorly understood. A key indicator of active magnetic reconnection is the ion diffusion region, but its detection at Jupiter had not been confirmed previously. Here, we report a magnetic reconnection event in Jupiter’s inner magnetosphere that presents the detection of an ion diffusion region. We provide evidence that this event involves localized flux tube interchange motion driven by centrifugal forces, which occurs inside a thin current sheet formed by the collision and twisting of two distinct flux tubes. This study provides insights into Io-genic plasma transport at Jupiter and the unique role of magnetic reconnection in rapidly rotating systems, two key unresolved questions.

Abstract Coronal mass ejections (CMEs) release between ≈10 30 and 10 33 erg of energy into the corona; however, their detailed energy budget is difficult to constrain. In the first paper of the series, we used a magnetohydrodynamics (MHD) model to simulate the 2008 April 9 CME (“Cartwheel CME”) and its Hinode/Extreme ultraviolet Imaging Spectrometer observations at 1.1 R ⊙ , performing a detailed analysis of the thermodynamic evolution during the initial acceleration period. This is the first global MHD simulation of a CME to include self-consistent prediction of charge states and nonequilibrium ionization spectra. In this second paper, we extend the results to investigate the energy budget evolution during the Cartwheel CME’s initial acceleration period by analyzing the 3D global structure and tracking multiple plasma parcels to examine their energy evolution. Early in the eruption, 70% of the magnetic energy stored in the flux rope either dissipates to the thermal or is converted to kinetic energy, while about 30% of the energy is lost primarily to radiation. The protons are preferentially heated in the sheath by increased Alfvén wave energy dissipation. An extended current sheet forms out to 1.6 R ⊙ , resulting in reconnection, which drives a hot jet along the backside of the flux rope. The prominence material remains cold beyond 10 R ⊙ , due to large radiative cooling rates.

Abstract Remote brightening (RB) refers to brightening at a footpoint of magnetic loops in the solar atmosphere, which is passively triggered by an eruption occurring at the other footpoint. Here, we present observations of an RB event driven by an extreme-ultraviolet (EUV) jet. The leading front of the jet exhibits flows exceeding the characteristic sound speed, and it triggers RBs at two remote sites that are connected by coronal loops. We focus on the RB that occurred at one of the footpoints, in which the magnetic structure is characterized by a dome-like feature with magnetic null points. When the jet propagates to this footpoint, the brightening displays a distinct inverted-Y-shaped structure. Bidirectional flows with a velocity of about 30 km s −1 are detected in any two branches of this structure, which are suggestive of the occurrence of magnetic reconnection at this footpoint. To investigate the physics of the interaction between the jet and the remote magnetic null point, we conducted a 2D MHD simulation with adaptive mesh refinement. We find that the collapse of the magnetic null point is induced by a fast-mode wave, and the flow associated with the jet elongates the current sheet, thereby triggering plasmoid instability. Subsequent magnetic reconnection not only forms the bright inverted-Y-shaped structure but also drives bidirectional flows along the structures, being consistent with the observational findings. This study provides new insights into the dynamic interaction between EUV jets and remote magnetic nulls in the solar atmosphere, and helps understand the diverse natures of RBs.

Magnetic reconnection accelerates electrons in both space and lab plasmas. The source of energy for this acceleration is the reconnecting magnetic field component. For fully ion-coupled reconnection in a one-dimensional current sheet, the efficiency and mechanism for electron acceleration are a strong function of the strength of the “guide” magnetic field directed perpendicular to the plane of reconnection. When the guide field is strong, the mechanism for electron acceleration is the parallel electric field, and it becomes less efficient with increasing guide field. We present data from studies of electron acceleration in the PHAse Space MApping (PHASMA) experiment, which induces reconnection between two electron-scale magnetic flux ropes. Our measurements show decreasing electron acceleration as the guide field is increased from 5 to 25 times the reconnecting field strength, with the input magnetic energy associated with the reconnecting component held constant. Electron acceleration is inferred from retarding field energy analyzer measurements, which complement measurements from a Thomson scattering diagnostic. The observed energies are consistent with the energy gain expected from acceleration via the parallel electric field, whereas estimates for expected energy gains from the Fermi acceleration fall well short of the observed values. Magnetic measurements show that the current sheet's thickness increases when the guide field is increased from 10 to 25. A thicker current sheet is believed to weaken the parallel electric field, consistent with the observed diminishment in electron acceleration.

Abstract 1D self‐consistent model of super‐thin current sheet (STCS) based both on a quasi‐adiabatic approach for the demagnetized proton and electron motion is generalized to the case of configuration with non‐zero guide field. The part of electron population is supposed to be magnetized (described via guiding center approximation). The magnetic field configuration includes three components: self‐consistent and components maintained by current components and respectively, plus a constant component in GSM coordinates. We constructed a transition from intense STCSs supported by quasi‐adiabatic electrons with high velocity anisotropy to less intense and thicker current sheets (CSs) supported by magnetized electrons with pressure anisotropy as the guide field increases and the system equilibrium approaches a force‐free configuration. Our model is capable to describe two distinct regimes: (a) intense STCSs supported by demagnetized electrons with a weak guide field (, where is the magnetic field amplitude at the CS edge), and (b) quasi‐force‐free configurations with a strong guide field . Analysis of 181 STCS crossings by MMS spacecrafts reveals a critical discrepancy. For a strong guide field, the modeled stationary configurations of electron CSs broaden and weaken, in contrast to the observed CSs, which remain super‐thin, exhibit clear non‐stationarity and are accompanied by the generation of a strong electric field.