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The triggering mechanism of the substorm onset has been a major issue in magnetospheric research. Various models have been proposed so far. To understand the causal relationship of magnetotail processes associated with substorm onsets, our previous studies performed a series of statistical analyses of Geotail and Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft data. We obtained the overall morphological picture of magnetotail evolution associated with substorm onsets and found that near-Earth magnetic reconnection plays a key role in substorm expansion triggering, energy release, and reconfiguration. In these previous studies, we took only one timing of initial auroral brightening as the substorm onset, based on space-based or ground-based auroral imager data. Our recent detailed analyses of ground-based auroral imager data, however, showed that the auroral onset arc develops stepwise: preonset fading, initial brightening, further enhancement of the onset arc, and poleward expansion. To understand the substorm triggering mechanism in more detail, this paper attempts to clarify the connection of the auroral onset arc's stepwise development with magnetotail processes of magnetic reconnection, flow, wave, and dipolarization. In this context, we reinterpret the substorm onset of our previous statistical studies as auroral onset arc enhancement or poleward expansion. Furthermore, for future detailed studies of the stepwise auroral and magnetotail development including pseudosubstorm (pseudobreakup), it might be better to call the transition period from initial brightening to the beginning of poleward expansion "onset/initial/trigger phase". [ABSTRACT FROM AUTHOR]

The solar chromosphere is a crucial layer for resolving the problem of atmospheric heating. There are many bright features, which are considered as the thermal signals for heating the atmosphere, and these features are suggested to have resulted from either magnetic reconnection or wave dissipation. It has been reported that a large number of propagating bright knots are detected in the chromosphere and corona. In this paper, we employ the high-resolution chromospheric H α data from the New Vacuum Solar Telescope to study the propagating bright knots. As the propagating bright knots move along the chromospheric fibrils, we select isolated and clear fibrils and track the knots along these fibrils. While the number of knots in a fibril region is equal to or greater than 5, the fibril and the knots are recorded. Based on the data on 2019 September 4, we detected 98 knots, and these knots move along 13 fibrils. On 2019 November 2, 87 knots, which move along 12 fibrils, were recorded. These propagating bright knots have an average area of around 0.8 Mm2, with propagating distances from 190 to 2450 km, propagating velocities from 5 to 51 km s−1, and an average lifetime of 71 s. To examine the relationship between the knots and the photospheric magnetic fields, we measure the field underneath these knots. The average magnetic flux densities are less than 10 Gauss, comparable with the noise level. We suggest that these knots are not produced by magnetic reconnection, but rather by wave dissipation. [ABSTRACT FROM AUTHOR]

In the solar corona, magnetically sheared structures are unstable to both tearing and thermal instabilities in a coupled fashion. However, how the choice of linear perturbation modes influences the time-scale to achieve the thermal runaway in a coupled tearing–thermal coronal current sheet is not well understood to date. Here, we model a force-free Harris current sheet under solar coronal conditions to investigate this coupling in the linear and non-linear regimes. In the linear regime, we adopt the magnetohydrodynamic spectroscopy code legolas to compare the current sheet under thermal and thermoresistive conditions, after which we initialize non-linear simulations (with mpi-amrvac) with the unstable, linear tearing and thermal perturbations obtained with legolas. It is shown that part of the unstable thermal quasi-continuum adopts tearing properties in the linear stage, but that it is not until the non-linear stage is reached that a true thermal 'runaway' effect leads to condensations inside tearing-induced flux ropes. Hence, the linear stage is governed by the dominant tearing instability whilst condensations form due to tearing–thermal coupling in the non-linear stage. Our results imply that perturbing an equilibrium current sheet with the fastest growing linear mode skips the mode-mixing phase in which the dominant instability traditionally emerges, and significantly reduces the time-scale to enter into the non-linear stage and thermal runaway process from its equilibrium configuration. [ABSTRACT FROM AUTHOR]

This work presents a laboratory experiment on the magnetic reconnection of two self-sustained, tilt-unstable spheromaks. Experimental observations, confirmed by a developed 3D Hall-MHD model, demonstrate that magnetic reconnection of these spheromaks suppresses the tilt instability by reducing the amplitudes of disruptive low-number toroidal modes. The strong toroidal component of outflow jets generates a shear toroidal velocity, which may disrupt the coherent structure of these modes, leading to their suppression. The damping rate of toroidal magnetic perturbations was found to be exponentially related to the shear toroidal velocity. Following the end of reconnection, the growth rate of the modes is linearly proportional to the decrease in shear velocity. [ABSTRACT FROM AUTHOR]

The failure of a filament eruption caused by magnetic reconnection between the erupting filament and the overlying magnetic field has been previously proposed in numerical simulations. It is, however, rarely observed. In this study, we report a reconnection between an erupting filament and its overlying coronal loops that results in the failure of the filament eruption. On 2023 September 24, a filament was located in active region 13445. It slowly rose, quickly erupted, rapidly decelerated, then finally stopped, with an untwisting motion. As a failed eruption, the event is associated with an M4.4 flare but no coronal mass ejection. During the eruption, the filament became bright, and the overlying loops appeared first in the high-temperature channels. They have average temperatures of ∼12.8 and ∼9.6 MK, respectively, indicating that both of them were heated. Two sets of new loops, separately connecting the filament endpoints and the overlying loop footpoints, then formed. Subsequently, the heated overlying loops were seen sequentially in the low-temperature channels, showing the cooling process, which is also supported by the light curves. Plasmoids formed and propagated bidirectionally along the filament and the overlying loops, indicating the presence of plasmoid instability. These results suggest that reconnection occurs between the erupting filament and the overlying loops. The erupting filament eventually disappeared, with the appearance of more newly formed loops. We propose that the reconnection between the erupting filament and the overlying loops ruins the filament completely, hence resulting in the failed eruption. [ABSTRACT FROM AUTHOR]

A statistical analysis of energy transport through Earth's plasma sheet is performed using 6 years of Magnetospheric Multi-Scale (MMS) mission observations. The analysis entails a complete decomposition of the contributions to transport including the ion heat flux and enthalpy flux derived from the full ion pressure tensor to provide a three-dimensional (3-D) picture of plasma sheet energy transport. It is shown that the Poynting flux and enthalpy flux compete to dominate the total energy transport, while the heretofore ignored heat flux generally contributes a larger fraction of the total energy flux than the bulk kinetic energy flux. The spatial distribution of these fluxes are consistent with magnetic reconnection driven transport from an X-line statistically located at X ∼ − 20 R E . Kinetic fluxes stream Earthward from this point peaking mid-tail along the neutral sheet, while Poynting fluxes peak at higher latitudes and along the inner edge of the plasma sheet. [ABSTRACT FROM AUTHOR]

Field-particle energy exchange is important to the magnetic reconnection process, but uncertainties regarding the time evolution of this exchange remain. We investigate the temporal dynamics of field-particle energy exchange during magnetic reconnection, using Magnetospheric Multiscale mission observations of an electron-only reconnection event in the magnetosheath. The electron energy is in local minimum at the x-line due to a density depletion, while the magnetic energy is in local maximum due to a guide field enhancement. The electromagnetic energy transport comes almost entirely from guide field contributions and is confined within the reconnection plane, while the most significant contribution to electron energy transport is independent of the drift velocity with additional out-of-plane signatures. Multi-spacecraft analysis suggests that the guide field energy is decreasing while the electron density is increasing, both evolving such that the system is moving toward a more uniform distribution of magnetic and thermal energy. The exchange of electromagnetic and thermal energy in collisionless plasmas is an important area of study to understand many space physics processes. The authors use in-situ, high resolution measurements from the MMS mission to examine the spatiotemporal evolution of the electron thermal and electromagnetic energy landscape during an encounter with a magnetic reconnection site in the Earth's magnetosphere. [ABSTRACT FROM AUTHOR]

We describe a novel splitting approach to numerical relativistic magnetohydrodynamics (RMHD) designed to expand its applicability to the domain of ultrahigh magnetization (high- |$\sigma$|⁠). In this approach, the electromagnetic field is split into the force-free component and its perturbation due to the plasma inertia. Accordingly, the system of RMHD equations is extended to include the subsystem of force-free degenerate electrodynamics and the subsystem governing the plasma dynamics and the perturbation of the force-free field. The combined system of conservation laws is integrated simultaneously, to which aim various numerical techniques can be used, and the force-free field is recombined with its perturbation at the end of every time-step. To explore the potential of this splitting approach, we combined it with a third-order weighted essentially non-oscillatory method, and carried out a variety of 1D and 2D test simulations. The simulations confirm the robustness of the splitting method in the high- |$\sigma$| regime, and also show that it remains accurate in the low- |$\sigma$| regime, all the way down to |$\sigma =0$|⁠. Thus, the method can be used for simulating complex astrophysical flows involving a wide range of physical parameters. The numerical resistivity of the code obeys a simple ansatz and allows fast magnetic reconnection in the plasmoid-dominated regime. The results of simulations involving thin and long current sheets agree very well with the theory of resistive magnetic reconnection. [ABSTRACT FROM AUTHOR]

The Detection and EUV Flare Tracking (DEFT) tool automatically identifies flare precursors in extreme ultraviolet (EUV) observations in a fast and consistent manner, with minimal computational overhead. DEFT currently uses GOES/SUVI 304 Å observations to detect, group, and flag sudden impulses that could be precursors to flares. In this study, we analyzed precursor signatures before 351 flares (150 C, 150 M, and 51 X class flares) that occurred from 2017 to date. Across these magnitudes, precursors were detected for 93% of the flares when using a 6 hr window before the flare start times. Using superposed epoch analysis, we found that elevated precursor activity tends to occur across all magnitude flares in the last 2 hr before the flares. The frequency of precursors gradually increases before M class flares but decreases for C class flares. We also found that in the last 20 minutes there is a significantly higher precursor frequency, pixel count, and power associated with M class flares than C class flares. We suggest that the observed EUV precursors are the observable signatures of small-scale magnetic reconnection events, and the consistently increasing frequency of precursor activity could indicate that the region is becoming increasingly unstable and reaching a critical stage that could result in flare initiation. Continuing research on EUV precursors is essential to better understand preflare processes that build and reduce magnetic instability prior to main-stage flares. The consistent and reliable detection and differentiation of EUV precursors could also complement and significantly improve current flare forecasting efforts. [ABSTRACT FROM AUTHOR]

Magnetic flux ropes are a fundamental component in both space and laboratory plasmas. We present a Hall-MHD simulation exploring the interaction between two isolated magnetic flux ropes under mesoscale solar wind conditions. The interaction interface is resolved with a resolution approaching the kinetic scale, to reveal unprecedented details of this process. As we replicate previous findings that such interactions can lead to the formation of two new ropes, we also find that magnetic reconnection occurs in multiple locations inside the central current sheet, leading to transient small flux ropes, which is qualitatively consistent with previous magnetospheric multiscale observations. Consequently, each field line undergoes multiple reconnections that alter its connectivity before it exits the current sheet. Later, each flux rope divides into two branches: the reconnected flux moving away from the current sheet to form the transition regions of the new ropes and the remnant flux sustaining the current sheet. For each magnetic flux rope (MFR), the core field reconnects after most surface fields are reconnected so that the reconnecting MFRs maintain a relatively symmetric shape. These results in unprecedented detail highlight the complex internal dynamics and call for further observational and theoretical studies. [ABSTRACT FROM AUTHOR]

During relativistic magnetic reconnection, antiparallel magnetic fields undergo a rapid change in topology, releasing a large amount of energy in the form of non-thermal particle acceleration. This work explores the application of mesh refinement to 2D reconnection simulations to efficiently model the inherent disparity in length-scales. We have systematically investigated the effects of mesh refinement and determined necessary modifications to the algorithm required to mitigate non-physical artifacts at the coarse–fine interface. We have used the ultrahigh-order pseudo-spectral analytical time-domain Maxwell solver to analyze how its use can mitigate the numerical dispersion that occurs with the finite-difference time-domain (or "Yee") method. Absorbing layers are introduced at the coarse–fine interface to eliminate spurious effects that occur with mesh refinement. We also study how damping the electromagnetic fields and current density in the absorbing layer can help prevent the non-physical accumulation of charge and current density at the coarse–fine interface. Using a mesh refinement ratio of 8 for two-dimensional magnetic reconnection simulations, we obtained good agreement with the high-resolution baseline simulation, using only 36% of the macroparticles and 71% of the node-hours needed for the baseline. The methods presented here are especially applicable to 3D systems where higher memory savings are expected than in 2D, enabling comprehensive, computationally efficient 3D reconnection studies in the future. [ABSTRACT FROM AUTHOR]

Recent observations show very near‐Earth reconnection (∼8–13RE) could efficiently power the ring current during the main phase of geomagnetic storms, but whether the recovery phase might be contributed remains unclear. During the recovery phase of the May 2024 major geomagnetic storm, intense auroral brightening and geomagnetic disturbances were observed at midnight, indicative of particle injections. Current wedges observed by mid‐latitude ground magnetometers around midnight suggest dipolarizing flux bundles (DFBs). The latitude of the auroral brightening was clearly lower than usual, suggesting near‐Earth reconnection (NERX) was closer to Earth than during substorms (∼20–30RE). GOES‐18 at midnight detected magnetic field and plasma signatures consistent with DFBs, following an extremely thin current sheet likely compressed by strong upstream dynamic pressure. These results indicate NERX could have been close enough for resultant DFBs to penetrate geosynchronous orbit and contribute to the ring current during the recovery phase. This scenario deserves further examination in future. Plain Language Summary: When a coronal mass ejection hits Earth's magnetic field, significant disturbances in the near‐Earth space environment occur, namely geomagnetic storms, causing many hazards to our power systems and space missions. It is thus important to understand the underlying processes, especially how energetic particles are transported from the nightside to energize these disturbances. Nightside magnetic reconnection, which converts magnetic energy to particle energy, was not widely considered as an efficient contributor because it typically occurs too far from Earth. However, by identifying observational characteristics using ground and spacecraft measurements, we find that such magnetic reconnection could be sufficiently close to Earth to transport energy and particles to geosynchronous orbit during the recovery phase of a geomagnetic storm. Our results improve our understanding of energy transport during the recovery phase, which will help understand and mitigate space weather hazards in the future. Key Points: During the recovery phase of the May 2024 major storm, near‐Earth reconnection was likely close enough to contribute to the ring currentDipolarizing flux bundles penetrated to ∼6.6RE at midnight with current wedges, auroral brightening, and ionospheric currents identifiedThe driver was likely a large dynamic pressure that strongly compressed the magnetosphere, causing an extremely thin current sheet at ∼6.6RE [ABSTRACT FROM AUTHOR]

The Dungey cycle is considered from the formation of a magnetic barrier and necessary for dayside reconnection conditions till the electric field generation around the Birkeland current loop and magnetic flux circulation balance. Data-based modeling of the magnetosheath magnetic field makes it possible to quantitatively assess the main factors that control formation and destruction of the magnetospheric magnetic barrier, such as the field line draping and the field intensity increase from the bow shock to the magnetopause, as well as their dependence on the orientation of the interplanetary magnetic field (IMF). The Dungey cycle has been revised to take into account the essentially time-dependent effects of magnetic reconnection. It is shown by means of the Stokes' theorem that a powerful electric field with an effective potential difference of several tens of kV is generated around the developing substorm current system. The emerging Birkeland current loop is an important particle acceleration element in the magnetosphere, contributing to the energization of ring current protons and electrons. The electric field that arises in the dipolarization zone magnifies the already existing ring current, and the closure of its amplified part through the ionosphere generates the Region 2 field-aligned currents. The motion of the expanding partial ring current around the magnetosphere, combined with the particle drift, transfers the magnetic flux from the night side of the magnetosphere to the dayside. At the dayside magnetopause, the reconnection is also responsible for the creation of the Birkeland loop, but now the electric field in the loop area decelerates the ring current particles, and regions of weakened ring current are formed. Closure of these weakened loop currents results in a transfer of the magnetic flux from the dayside to the night side, thus ensuring its overall balance and completing the Dungey cycle. [ABSTRACT FROM AUTHOR]

Magnetic reconnection regions in space and astrophysics are known as active particle acceleration sites. There is ample evidence showing that energetic particles can take a substantial amount of converted energy during magnetic reconnection. However, there has been a lack of studies understanding the backreaction of energetic particles at magnetohydrodynamical scales in magnetic reconnection. To address this, we have developed a new computational method to explore the feedback by nonthermal energetic particles. This approach considers the backreaction from these energetic particles by incorporating their pressure into magnetohydrodynamics (MHD) equations. The pressure of the energetic particles is evaluated from their distribution evolved through Parker's transport equation, solved using stochastic differential equations (SDEs), so we coin the name MHD-SDE. Applying this method to low- β magnetic reconnection simulations, we find that reconnection is capable of accelerating a large fraction of energetic particles that contain a substantial amount of energy. When the feedback from these particles is included, their pressure suppresses the compression structures generated by magnetic reconnection, thereby mediating particle energization. Consequently, the feedback from energetic particles results in a steeper power-law energy spectrum. These findings suggest that feedback from nonthermal energetic particles plays a crucial role in magnetic reconnection and particle acceleration. [ABSTRACT FROM AUTHOR]

Understanding electron kinetic processes is crucial for elucidating the energy conversion mechanisms in magnetic reconnection. Non‐Maxwellian electron distributions are strong indicators of kinetic‐scale processes near the electron diffusion region, yet they remain incompletely understood. Using in‐situ spacecraft data from 29 magnetopause reconnection events, we unambiguously identify a non‐Maxwellian capsule electron distribution near the electron diffusion region. This distribution comprises an elongated component parallel with the magnetic field at lower energies and a butterfly component (with peaks at pitch angles near 45° $45{}^{\circ}$ and 135° $135{}^{\circ}$) at higher energies. We provide evidence that these distributions are partly linked to electron trapping and preferential heating along the direction of magnetic fields. The parallel electric potentials needed for the parallel heating may be linked to kinetic Alfvén waves. These capsule‐like electron distributions are also found to generate whistler emissions. Our results suggest that these kinetic processes are prevalent in magnetic reconnection. Plain Language Summary: Understanding how electrons behave in space plasmas, especially during magnetic reconnection, is crucial. Using data from spacecraft, we studied electron behavior near this reconnection region and identified a unique pattern called a capsule distribution. This distribution combines two shapes: an elongated component at lower energies and a butterfly like component at higher energies. These distributions are closely linked to whistler wave emissions. Our research provides evidence that these capsule‐like distributions indicate electron trapping and heating by parallel electric fields. The parallel electric field and electric potentials may be related to kinetic Alfven waves. These kinetic processes, captured by emitted whistler waves, are prevalent near the diffusion region, offering deeper insights into electron heating during magnetic reconnection. Key Points: Non‐Maxwellian capsule electron distributions near the electron diffusion region comprises an elongated component and a butterfly componentCapsule‐like electron distributions generate whistler emissions in the presence of unusual temperature anisotropy T‖/T⊥<1 $\left({T}_{\Vert }/{T}_{\perp }< 1\right)$Capsule electron distributions suggest electron trapping and preferential heating by parallel electric fields [ABSTRACT FROM AUTHOR]

A three‐dimensional particle‐in‐cell simulation is performed to study secondary reconnection between two interlinked flux tubes produced by neighboring guide field reconnection x‐lines. The reconnecting magnetic fields of this secondary reconnection is enhanced toward the diffusion region, agree well with that in observations. The magnetic field pileup is attributed to the upstream magnetic tension force, that smashes the flux tubes into each other. We propose that the primary reconnection x‐line length is a key parameter to determine the formation of interlinked flux tubes and secondary reconnection therein. Interlinked flux tubes will form only if the x‐line is short; when the x‐line is long enough, the regular flux ropes are formed instead. The critical x‐line length to form interlinked flux tubes is determined by the distance between two neighbor x‐lines and the magnetic shear angle of the primary reconnection. The results provide a novel scenario of secondary reconnection generation during three‐dimensional reconnection. Plain Language Summary: Magnetic reconnection is a fundamental energy conversion process in plasmas, and exists in varieties of space environments. Recent observations find magnetic reconnection occurring in the current sheet between two elbow like flux tubes interlinked with each other. The observational features of such a kind of event are very similar to that of a flux rope, which is a helical magnetic field structure. However, the formation condition for interlinked flux tubes and magnetic reconnection between them is not well understood, the relation between interlinked flux tubes and flux ropes is also not very clear. In this letter, we use three‐dimensional particle‐in‐cell simulation to study the formation of magnetic reconnection between interlinked flux tubes, and propose an explanation for its formation. Key Points: Interlinked flux tubes can form during multiple x‐line guide field reconnection when the x‐line is shortSecondary reconnection can be triggered in the current sheet formed between interlinked flux tubesThe upstream magnetic field pileup is caused by the magnetic tension force [ABSTRACT FROM AUTHOR]

Measurement of a jet geometry transition region is an important instrument of assessing the jet ambient medium properties, plasma bulk motion acceleration, parameters of a black hole, and location of a jet-launching radius. In this work, we explore the possibility of a presence of a core shift break, associated with the geometry and jet physical properties transition. We obtain the relations on the core shift offset jump due to a change in a core shift exponent. The condition of a proper frame magnetic field continuity and the core shift break can be used as an instrument to refine the magnetic field estimates upstream the break. This method is applied to the jet in NGC 315. We also argue that a local change in the plasma properties in the jet, for example due to the occurrence of a standing shock or a magnetic field reconnection, will also affect the dependence of the core shift on frequency. The properties of such a jump will be different than in the previous case. We propose to use the multifrequency core shift measurements to increase the number of sources with a detected jet shape break and to boost the accuracy of assessing the properties of a jet geometry transition region. [ABSTRACT FROM AUTHOR]

We present the first model aimed at understanding how the Meissner effect in a young neutron star affects its macroscopic magnetic field. In this model, field expulsion occurs on a dynamical time-scale, and is realized through two processes that occur at the onset of superconductivity: fluid motions causing the dragging of field lines, followed by magnetic reconnection. Focusing on magnetic fields weaker than the superconducting critical field, we show that complete Meissner expulsion is but one of four possible generic scenarios for the magnetic-field geometry, and can never expel magnetic flux from the centre of the star. Reconnection causes the release of up to |$\sim 5\times 10^{46}\, \mathrm{erg}$| of energy at the onset of superconductivity, and is only possible for certain favourable early-phase dynamics and for pre-condensation fields |$10^{12}\, \mathrm{G}\lesssim B\lesssim 5\times 10^{14}\, \mathrm{G}$|⁠. Fields weaker or stronger than this are predicted to thread the whole star. [ABSTRACT FROM AUTHOR]

We report on the formation of a large magnetic coherent structure in a vortex expansion–contraction interval, resulting from the merger of two plasmoids driven by a supergranular vortex observed by Hinode in the quiet-Sun. Strong vortical flows at the interior of vortex boundary are detected by the localized regions of high values of the instantaneous vorticity deviation, and intense current sheets in the merging plasmoids are detected by the localized regions of high values of the local current deviation. The spatiotemporal evolution of the line-of-sight magnetic field, the horizontal electric current density, and the horizontal electromagnetic energy flux is investigated by elucidating the relation between velocity and magnetic fields in the photospheric plasma turbulence. A local and continuous amplification of magnetic field from 286 G to 591 G is detected at the centre of one merging plasmoid during the vortex expansion–contraction interval of 60 min. During the period of vortex contraction of 22.5 min, the line-of-sight magnetic field at the centre of plasmoid-1 (2) exhibits a steady decrease (increase), respectively, indicating a steady transfer of magnetic flux from plasmoid-1 to plasmoid-2. At the end of the vortex expansion–contraction interval, the two merging plasmoids reach an equipartition of electromagnetic energy flux, leading to the formation of an elongated magnetic coherent structure encircled by a shell of intense current sheets. Evidence of the disruption of a thin current sheet at the turbulent interface boundary layers of two merging plasmoids is presented. [ABSTRACT FROM AUTHOR]

In this paper, we carry out multiwavelength and multiview observations of the prominence eruption, which generated a C2.3 class flare and a coronal mass ejection (CME) on 2023 March 7. For the first time, we apply the revised cone model to three-dimensional reconstruction and tracking of the eruptive prominence for ∼4 hr. The prominence propagates nonradially and makes a detour around the large-scale coronal loops in active region NOAA 13243. The northward deflection angle increases from ∼36° to ∼47° before returning to ∼36° and keeping up. There is no longitudinal deflection throughout the propagation. The angular width of the cone increases from ∼30° and reaches a plateau at ∼37°. The heliocentric distance of the prominence rises from ∼1.1 to ∼10.0 R ☉, and the prominence experiences continuous acceleration (∼51 m s−2) over 2 hr, which is probably related to the magnetic reconnection during the C-class flare. The true speed of the CME front is estimated to be ∼829 km s−1, which is ∼1.2 times larger than that of the CME core (prominence). We conclude that both acceleration and deflection of eruptive prominences in their early lives could be reproduced with the revised cone model. [ABSTRACT FROM AUTHOR]

Radio galaxies are a subclass of active galactic nuclei that drive relativistic jets from their center and are observed in radio to very-high-energy gamma rays. The emission mechanisms and regions are still unknown. High-energy gamma rays can be explained by the emission from the magnetically arrested disks (MADs) around the central supermassive black hole (BH), for which the magnetic flux threading the BH is in a saturation level, although the emission from the MADs does not explain the optical and X-ray data. We construct a two-zone multiwavelength emission model in which optical and X-rays come from jets, while millimeter/submillimeter and gamma rays come from MADs. Our model takes into account the particle injection by the magnetic reconnection at the jet base close to the BH and particle entrainment from the ambient gas at the jet emission zone. We apply our model to M87 and find that our model can explain the simultaneous multiwavelength data, except for the radio data, which could be explained if we extend our one-zone emission model to a one-dimensional one. We also find that the strong plasma entrainment is necessary to explain the multiwavelength data. Our model will be tested by variability analysis among the multiwavelength data. [ABSTRACT FROM AUTHOR]

Magnetic reconnection in the near-Earth magnetotail is responsible for explosive release of energy during substorms and auroral breakups. This near-tail reconnection was previously assumed to occur around the midnight meridian, where earthward flows were typically observed. Based on observations of tailward-moving plasmoids, the Geotail spacecraft mission discovered that the reconnection location was displaced toward dusk. This dusk preference is presumably caused by the Hall electric field, as was suggested later in simulations. However, recent spacecraft observations have indicated that the reconnection was displaced toward dawn, and not dusk, in Mercury's magnetotail. In response to this controversy, our study aims to clarify the dawn–dusk location of fast plasma flows in the near-Earth magnetotail. Through a comprehensive reinterpretation and integration of previous statistical results, we found that the dusk preference is generally evident for tailward flows but is often absent for earthward flows. These results indicate that the statistical results of earthward flows are sensitive to event selection criteria. We conclude that the dawn–dusk location of earthward flow is statistically unclear at the time of substorm onset. Similarly, in the magnetotail of other planets, the dawn–dusk location of planetward flow may be sensitive to event selection criteria. Hence, reconnection may occur predominantly on the duskside in Mercury's magnetotail. This hypothesis will be tested using observations of tailward-moving plasmoids by the BepiColombo Mio spacecraft, which will begin orbital observations of Mercury in the year 2026. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is a basic particle acceleration mechanism in laboratory and astrophysical plasmas. Two-dimensional models have been critical to understanding the onset of reconnection in laboratory experiments, but are fundamentally limited in diagnosing ion acceleration along open magnetic field lines. These shortcomings have opened the way to three-dimensional (3-D) models of torsional reconnection, where localized rotational perturbations to a fan-spine magnetic null point topology have demonstrated bulk particle acceleration along open magnetic field lines. Previous computational studies of the torsional fan reconnection mode using both solar and laboratory parameters demonstrated collimated jet formation and acceleration along the spine axis, wherein the bulk particle final kinetic energy spectra were shown to fall within a relatively narrow range (${\sim }2$  keV). This paper introduces typical laboratory plasma parameters in the torsional spine mode of 3-D reconnection models to diagnose its efficacy in inducing rapid ion acceleration. Using laboratory-scale length helium plasma parameters typical of capacitive discharges (singly ionized helium), we solve for relativistic particle trajectories using solutions to the steady-state, resistive, kinematic magnetohydrodynamic equations in the fan-spine topology. We find that particle acceleration at the reconnection site is highly dependent on the injection radius, and the peak accelerated particles ($\approx$ 3 keV) are trapped about the magnetic null point. While a jet is formed by ions injected close to the peak fan plane perturbation radius, their final ion kinetic energies are an order of magnitude lower ($\approx$ 0.3 keV) than the mirrored particles. Analysing the time dependence of their limited representative energy spectra shows the torsional spine mode particles follow an evolution much different than the narrow spectra of the torsional fan mode. These results have implications for diagnostic expectations of future laboratory plasma experiments designed to induce the torsional spine reconnection mode. [ABSTRACT FROM AUTHOR]

MMS four-spacecraft observations with high temporal and spatial resolution made it possible to study the characteristics of intense superthin current sheets (SCSs) with a current density J > 30 nA/m2, formed in bursty bulk flows (BBFs), propagating in the Plasma Sheet (PS) of the magnetotail from the remote X line. Statistical analysis of >1000 SCSs observations showed that, in the majority of cases, the current in the SCSs is parallel to the ambient magnetic field and is carried by field-aligned accelerated electron beams. The half-thickness of the SCSs is several electron gyroradii, and in such thin layers the electric current is carried by demagnetized electrons. Bursts of strong nonideal electric fields E' > 10 mV/m are often observed at the edges and/or inside the SCSs. The generation of such fields brings about energy conversion in the SCSs of hundreds of pW/m3, and in some cases up to several nW/m3, which is comparable to the energy conversion in the electron diffusion region of magnetic reconnection. The strongest energy release is observed in the SCSs formed in the fastest BBFs and under strong variations of the magnetic field in the tail lobes. [ABSTRACT FROM AUTHOR]

We study the evolution equation for magnetic energy density for a non-relativistic magnetized plasma in the (Lagrangian) reference frame comoving with the electron bulk velocity. Analyzing the terms that arise due to the ideal electric field, namely, perpendicular electron compression and magnetic field line bending, we recast them to reveal a quantity with a functional form analogous to the often-studied pressure–strain interaction term that describes one piece of internal energy density evolution of the species in a plasma, except with the species pressure tensor replaced by the magnetic stress tensor. We dub it the "magnetic stress–strain interaction." We discuss decompositions of the magnetic stress–strain interaction analogous to those used for pressure–strain interaction. These analogies facilitate the interpretation of the evolution of the various forms of energy in magnetized plasmas and should be useful for a wide array of applications, including magnetic reconnection, turbulence, collisionless shocks, and wave–particle interactions. We display and analyze all the terms that can change magnetic energy density in the Lagrangian reference frame of the electrons using a particle-in-cell simulation of magnetic reconnection. [ABSTRACT FROM AUTHOR]

Alongside magnetic reconnection, turbulence is another fundamental nonlinear plasma phenomenon that plays a key role in energy transport and conversion in space and astrophysical plasmas. From a numerical, theoretical, and observational point of view there is a long history of exploring the interplay between these two phenomena in space plasma environments; however, recent high-resolution, multi-spacecraft observations have ushered in a new era of understanding this complex topic. The interplay between reconnection and turbulence is both complex and multifaceted, and can be viewed through a number of different interrelated lenses - including turbulence acting to generate current sheets that undergo magnetic reconnection (turbulence-driven reconnection), magnetic reconnection driving turbulent dynamics in an environment (reconnection-driven turbulence) or acting as an intermediate step in the excitation of turbulence, and the random diffusive/dispersive nature of the magnetic field lines embedded in turbulent fluctuations enabling so-called stochastic reconnection. In this paper, we review the current state of knowledge on these different facets of the interplay between turbulence and reconnection in the context of collisionless plasmas, such as those found in many near-Earth astrophysical environments, from a theoretical, numerical, and observational perspective. Particular focus is given to several key regions in Earth's magnetosphere – namely, Earth's magnetosheath, magnetotail, and Kelvin-Helmholtz vortices on the magnetopause flanks – where NASA's Magnetospheric Multiscale mission has been providing new insights into the topic. [ABSTRACT FROM AUTHOR]

Large gradual solar energetic particle (SEP) events can pose a radiation risk to crewed spaceflight and a significant threat to near-Earth satellites; however, the origin of the SEP seed particle population, and how these particles are released, accelerated and transported into the heliosphere are not well understood. We analyze NOAA active region (AR) 12673, which was the source responsible for multiple large gradual SEP events during 2017 September, and found that almost immediately after each significant eruptive event associated with SEPs an enhanced Si/S abundance ratio was measured by Wind, consistent with the previous work by Brooks et al. The EUV Imaging Spectrometer (EIS) onboard Hinode took data roughly 8 hr before the second SEP event on 2017 September 6, which allowed the regions of enhanced Si/S abundance ratio in the AR to be determined. We have shown that the AR contains plasma with elemental abundance values detected in situ by Wind. In particular, the plasma originates from the core of the AR, similar to Brooks et al., but in the moss (footpoints) associated with hot sigmoidal AR loops. The sigmoid, which contains highly fractionated plasma, erupts and propagates toward an Earth-connected magnetic null point, providing a direct channel for the highly fractionated plasma to escape and be detected in the near-Earth environment. [ABSTRACT FROM AUTHOR]

The Lunar Environment heliospheric X-ray Imager (LEXI) is an instrument built to image x-rays from solar wind charge exchange in Earth's magnetosheath. Monitoring the position of the magnetopause at the inner boundary of the magnetosheath allows us to understand how magnetic reconnection regulates how energy from the solar wind is deposited into Earth's magnetosphere. LEXI is part of an upcoming lunar lander mission set to land in Mare Crisium. To repel unwanted charged particles, the instrument carries a permanent magnet array composed of 48 neodymium magnets. The array was designed to maximize charged particle deflection while minimizing stray magnetic fields, which could impact other instruments or spacecraft operation. A Runge–Kutta-based fully kinetic particle tracing model was created to evaluate the effectiveness of LEXI's unique charged particle deflector array. Combined with the other particle suppression measures of the instrument, including physical structures and filters, the simulations show proton and electron transmission to the LEXI detector is expected to be sufficiently reduced to allow successful imaging. The flexible simulation model can be generalized to be used in examining the magnetic deflector array effectiveness of other instruments whose signals could be compromised by unwanted charged particle contamination. [ABSTRACT FROM AUTHOR]

The low‐latitude boundary layer (LLBL) is a crucial region for the transfer of mass, momentum, and energy between the solar wind and the planetary magnetosphere. However, the processes of energy conversion within this layer are not well understood. In this study, the anomalous magnetic topology sublayers (AMTSs) within Earth's inner LLBL are investigated during the local reconnection inactive period, using data from the Magnetospheric Multiscale (MMS) mission. We present the first in situ observations showing that these AMTSs lead to significant energy conversion within the inner LLBL. The electron populations in AMTSs are dominated by either the magnetospheric or magnetosheath populations, creating a substantial electron temperature gradient between these sublayers. This temperature gradient, in turn, generates non‐ideal electric fields through the pressure gradient term. Our findings improve the understanding of dynamics in the planetary LLBL, highlighting the importance of AMTSs in the energy conversion process. Plain Language Summary: The low‐latitude boundary layer serves as a crucial transition zone and plays an important role in the coupling process between the solar wind and the planetary magnetosphere. Anomalous magnetic topology sublayers are newly discovered kinetic‐scale structures that are prevalent in the inner low‐latitude boundary layer. However, the role of these anomalous magnetic topology sublayers in the exchange of matter, momentum, and energy between the solar wind and the planetary magnetosphere remains unclear. In this study, we investigate the magnetic field topology and energy conversion within these anomalous magnetic topology sublayers using data from the Magnetospheric Multiscale (MMS) mission. Our results reveal the mechanisms of non‐ideal energy conversion within these sublayers and underscore their significances in the Sun‐Earth interaction. Key Points: Anomalous magnetic topology sublayers (AMTSs) in the inner low‐latitude boundary layer are observed during the reconnection inactive periodSignificant energy conversion associated with AMTSs is comparable to that in some electron diffusion regionsNon‐ideal electric fields around these AMTSs are provided by the electron pressure gradient term in the electron momentum equation [ABSTRACT FROM AUTHOR]

How magnetic reconnection is triggered or suppressed is an important outstanding problem. By considering pinching of a current sheet that has formed at non‐equilibrium, we show that the background plasma beta is a major controlling factor in the onset and nature of magnetic reconnection. A high plasma beta inhibits a current sheet from pinching down to kinetic scales required for collisionless reconnection, while a low beta facilitates it. A simple adiabatic model provides a good prediction for the reconnection‐enabled regions in thickness versus peak plasma beta space, which are confirmed by a series of particle‐in‐cell simulations with varying initial parameters. A strong dependency of the peak reconnection rate on the plasma beta is clearly predicted with reconnection being favored in low beta conditions. A finite guide field is an additional source of reconnection suppression, consistent with previous observations that reconnection requires a large enough magnetic shear angle for high‐beta situations. Plain Language Summary: Magnetic fields around the Sun and the Earth frequently release their stored energy into plasma energy in the form of a process called magnetic reconnection. However, this process does not occur in all situations, and so when and how it occurs is an outstanding question. In this paper, it is shown that a high plasma thermal pressure can counteract the magnetic pressure that would otherwise bring the fields to close proximity, preventing reconnection from happening. A component of the magnetic field that is not directly involved in reconnection, called the "guide field," also contributes to the suppression. Key Points: High plasma beta and/or guide field obstruct current sheet pinching to small scales required for collisionless reconnectionA simple adiabatic model predicts regions in parameters space where reconnection is enabled, verified by particle‐in‐cell simulationsThe tendency for reconnection onset aligns well with previous spacecraft observations [ABSTRACT FROM AUTHOR]

Spacecrafts observe signatures of duskside magnetic reconnection in the Earth's magnetotail associated with the presence of oxygen O+ $\left({\mathrm{O}}^{+}\right)$ ions of ionospheric origin. The exact role of O+ ${\mathrm{O}}^{+}$ ions in mediating reconnection remains largely unknown due to the local nature of observational techniques. We analyze results from global three‐dimensional hybrid (kinetic ions, fluid electrons) simulations of O+ ${\mathrm{O}}^{+}$ outflows and demonstrate that oxygen ions, escaping from the top of the ionosphere into the lobes, may cause disruptions on the duskside of the proton‐formed magnetotail, adding up to its turbulent, unsteady nature. These O+ ${\mathrm{O}}^{+}$ ions are shown to be capable of inducing magnetic flux ropes in the current sheet that thins out toward the dusk flank of the magnetotail due to Hall and ion kinetic effects. Unlike magnetohydrodynamics (MHD) simulations, where dawn‐dusk magnetotail asymmetries may develop due to nonuniform ionospheric conductivity, the hybrid simulations demonstrate duskside tail disruptions on much faster ion gyroscales. Plain Language Summary: Being one of the most important and ubiquitous elements of space weather, magnetic reconnection (breaking and merging of oppositely directed magnetic field lines in a plasma) globally governs the dynamics of the Sun‐Earth system. Current approaches to investigating this phenomenon in the Earth's magnetotail (the extension of the magnetosphere in the antisunward direction) largely assume that the magnetosphere is dominated by solar wind plasma, which mostly consists of protons. Recent satellite observations, however, have provided ample evidence of the important role played in magnetic reconnection by relatively cold ions of ionospheric origin, such as oxygen O+ $\left({\mathrm{O}}^{+}\right)$ ions. By conducting global three‐dimensional simulations, we account for full‐orbit dynamics of both solar wind protons and oxygen ions of ionospheric origin and show that intense flows of O+ ${\mathrm{O}}^{+}$ from the top of the ionosphere may modify and disrupt the near‐Earth magnetotail. In these simulations, we demonstrate the ability of oxygen ions to induce "magnetic flux ropes" (bundles of magnetic field lines of the same direction), confined to the duskside of the magnetotail, in agreement with observations. Physical effects responsible for the formation of these fundamental signatures of magnetic reconnection in the magnetotail are crucial to understanding and forecasting space weather. Key Points: Oxygen ions of ionospheric origin (O+) are shown to induce flux ropes in the near‐Earth magnetotail in hybrid simulationsO+ ions disrupt the plasma current sheet that thins out on the duskside due to Hall and ion kinetic effectsO+ induced flux ropes are confined to the dusk flank of the current sheet, in agreement with observations [ABSTRACT FROM AUTHOR]

Three-dimensional global hybrid simulations are performed to explore how the interplanetary magnetic field (IMF), the Martian crustal fields, and planetary pickup ions affect the twisting of the Martian magnetotail. The results agree with previous studies that the crustal magnetic fields cause the Martian magnetotail to twist counterclockwise or clockwise depending on the sign of the IMF Y -component in the Mars solar orbital coordinates. However, the twist is more pronounced when the crustal fields are on the nightside, contradicting the early explanation that the crustal fields affect the twist through dayside magnetic reconnection between the crustal fields and the draped IMF. Additionally, planetary pickup ions also contribute to the twist because their mass loading slows down the plasma flow and leads to the bending of the magnetic field lines in the magnetotail. It is demonstrated that the twist inside Mars' shadow in the near magnetotail region (at X = −1.5 R M, where R M is Mars' radius) is mainly attributable to the crustal fields, while the influence of planetary pickup ions starts to dominate outside Mars' shadow and in regions further away from Mars. [ABSTRACT FROM AUTHOR]

The orientation of Interplanetary Magnetic Field (IMF B) components plays a major role in magnetospheric Energetic Particles Precipitation (EPP). This is because the IMF B components in the Geocentric Solar Magnetospheric (GSM) coordinate system control magnetic reconnection at the subsolar magnetopause. This study intends to unravel the dependence of the preceding conditions of the orientations of IMF B components that drove geomagnetic storms on the EPPs produced in the Van Allen radiation belt. We classified the geomagnetic storms based on their drivers and IMF B z orientations prior to the storms' onset. Energetic particle fluxes, IMF B, and solar wind data were used. The study showed that electrons are more reactive to solar wind speed than protons. Additionally, storms with southward IMF B z orientation caused more EPP enhancement than with northward orientation. Our results also showed that protons are more influenced by magnetospheric compression than electrons at the northward orientation of IMF B z. In fact, at this point, the proton's motion violates adiabatic invariants. As particles interact with electric fields, a significant population of EPPs is produced by pitch angle diffusion. Generally, IMF B x and IMF B y are often anticorrelated. The preceding conditions of orientations of the IMF B x indicated weaker dependence on auroral indices, and invariably on energetic particles precipitation than the IMF B y. [ABSTRACT FROM AUTHOR]

Magnetic reconnection before flux cancellation in the solar photosphere when two opposite-polarity photospheric magnetic fragments are approaching one another is usually modelled by assuming that a small so-called 'floating current sheet' forms about a null point or separator that is situated in the overlying atmosphere. Here, instead we consider the reconnection that is initiated as soon as the fragments become close enough that their magnetic fields interact. The resulting current sheet, which we term a 'fin sheet' extends up from the null point or separator that is initially located in the solar surface. We develop here non-linear analyses for finite-length models of both fin and floating current sheets that extend the previous models that were limited to short floating current sheets. These enable the length of the current sheet and the rate of heating to be calculated in both cases as functions of the separation distance of the sources and the reconnection rate. Usually, the fin current sheet liberates more energy than a floating current sheet. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) from pseudostreamers represent a significant fraction of large-scale eruptions from the Sun. In some cases, these CMEs take a narrow jet-like form reminiscent of coronal jets; in others, they have a much broader fan-shaped morphology like CMEs from helmet streamers. We present results from a magnetohydrodynamic simulation of a broad pseudostreamer CME. The early evolution of the eruption is initiated through a combination of breakout interchange reconnection at the overlying null point and ideal instability of the flux rope that forms within the pseudostreamer. This stage is characterized by a rolling motion and deflection of the flux rope toward the breakout current layer. The stretching out of the strapping field forms a flare current sheet below the flux rope; reconnection onset there forms low-lying flare arcade loops and the two-ribbon flare footprint. Once the CME flux rope breaches the rising breakout current layer, interchange reconnection with the external open field disconnects one leg from the Sun. This induces a whip-like rotation of the flux rope, generating the unstructured fan shape characteristic of pseudostreamer CMEs. Interchange reconnection behind the CME releases torsional Alfvén waves and bursty dense outflows into the solar wind. Our results demonstrate that pseudostreamer CMEs follow the same overall magnetic evolution as coronal jets, although they present different morphologies of their ejecta. We conclude that pseudostreamer CMEs should be considered a class of eruptions that are distinct from helmet-streamer CMEs, in agreement with previous observational studies. [ABSTRACT FROM AUTHOR]

A method for prompt estimation of a number of key parameters that determine the features of the evolution and dynamics of current sheets produced in laboratory experiments has been proposed and realized experimentally. The method is based on the analysis of time dependences of the integral plasma current during its first half-period. The transverse dimensions of the current sheets and the strength of the initial electric field that initiates the sheet formation can be estimated on the base of defining the inductances of both the entire oscillatory contour and the region where the plasma current flows. Data on the plasma conductivity can be obtained by measuring the active resistance of the plasma gap and the dimensions of the current sheet. It is shown that the conductivity increased under conditions that corresponded to an increase in plasma density, indicating a turbulent nature of the conductivity. [ABSTRACT FROM AUTHOR]

Coronal mass ejections (CMEs) are often associated with X-ray (SXR) flares powered by magnetic reconnection in the low corona, while the CME shocks in the upper corona and interplanetary (IP) space accelerate electrons often producing the type II radio bursts. The CME and the reconnection event are part of the same energy release process as highlighted by the correlation between reconnection flux (ϕrec) that quantifies the strength of the released magnetic free energy during the SXR flare, and the CME kinetic energy that drives the IP shocks leading to type II bursts. Unlike the Sun, these physical parameters cannot be directly inferred in stellar observations. Hence, scaling laws between unresolved sun-as-a-star observables, namely SXR luminosity (LX) and type II luminosity (LR), and the physical properties of the associated dynamical events are crucial. Such scaling laws also provide insights into the interconnections between the particle acceleration processes across low-corona to IP space during solar-stellar "flare-CME-type II" events. Using long-term solar data in the SXR to radio waveband, we derived a scaling law between two novel power metrics for the flare and CME-associated processes. The metrics of "flare power" (Pflare = √(LXϕrec)) and "CME power" (PCME = √(LRVCME2)), where VCME is the CME speed, scale as Pflare ∝ PCME0.76 ± 0.04. In addition, LX and ϕrec show power-law trends with PCME with indices of 1.12 ± 0.05 and 0.61 ± 0.05, respectively. These power laws help infer the spatially resolved physical parameters, VCME and ϕrec, from disk-averaged observables, LX and LR during solar-stellar flare-CME-type II events. [ABSTRACT FROM AUTHOR]

Context. Dayside magnetodisc reconnection is a unique process that may occur in rapidly rotating magnetospheres with internal plasma sources, and it is not expected at Earth. Several observations suggest that dayside magnetodisc reconnection could be driven in the Kronian magnetosphere. This raises the question as to whether it can occur at Jupiter, the fastest rotating planet in the Solar System. Recent reports have suggested its occurrence, but the limited number of identified events leaves the overall global picture in the Jovian magnetosphere uncertain. Aims. The primary objective of this study is to answer whether dayside magnetodisc reconnection could exist within the Jovian magnetosphere through the use of global magnetohydrodynamics (MHD) simulations. Additionally, we aim to conduct a numerical investigation to reveal its general distribution for possible future exploration. Methods. The numerical simulations for Jovian magnetospheric dynamics are based on three-dimensional MHD calculations, which enable magnetic reconnection through numerical resistivity. In post-processing procedures, the simulated magnetodisc reconnection event is primarily identified by equatorial Bθ reversals, accompanied by an analysis of local plasma flows and global magnetic field lines. Results. Our global MHD simulations reveal the existence of magnetodisc reconnection within the dayside Jovian magnetosphere. The simulation results indicate that dayside magnetodisc reconnection is more likely to occur during solar wind rarefaction, primarily due to the rapid expansion of the dayside magnetospheric volume. This expansion allows a rotation-driven centrifugal force to generate sufficient magnetic field line stretching for current sheet thinning and reconnection. In simulated dayside events, Bθ reversals may occur locally or non-locally through rotational transport from reconnection sites at earlier magnetic local times. Conclusions. The existence and the features derived from simulations are testable as Galileo/Juno has accumulated a considerable amount of dayside magnetospheric data. These results are valuable for future Jovian missions, such as JUICE and Europa Clipper, and provide new insights into interpreting measurements from other rapidly rotating systems. [ABSTRACT FROM AUTHOR]

Context. Solar jets are collimated plasma ejections along magnetic field lines observed in hot (extreme-ultraviolet (EUV) jets) and cool (chromospheric surges) temperature diagnostics. Their trigger mechanisms and the relationship between hot and cool jets are still not completely understood. Aims. We aim to investigate the generation of a sequence of active-region solar jets and their evolution from the photospheric to the coronal heights using multithermal observations from ground-based and space-borne instruments. Methods. Using the synergy of high-spatial-resolution and high-temporal-resolution observations by the Swedish 1-m Solar Telescope (SST), along with the Solar Dynamics Observatory (SDO), we analyzed a sequence of solar jets originating in a mixed-polarity region between the leading and following sunspots of an active region. We investigated the kinematics of these jets using the spectra from the SST observations. We used a non-force-free field (NFFF) extrapolation technique to derive the magnetic field topology of the active region. Results. A mixed-polarity region is formed over a long period (24 hours) with persistent magnetic flux emergence. This region has been observed as an arch filament system (AFS) in chromospheric SST observations. In this region, negative polarities surrounded by positive polarities create a fan surface with a null point at a height of 6 Mm detected in the NFFF extrapolation. SST observations in the Hβ spectral line reveal a large flux rope over the AFS moving from north to south, causing successive EUV and cool jets to move in the east–west direction and later towards the south along the long open loops. Conclusions. The high-resolution SST observations (0″.038 per pixel) resolve the dark area observed at the jet base and reveal the existence of an AFS with an extended cool jet, which may be the result of a peeling-like mechanism of the AFS. Based on the combined analysis of SST and AIA observations along with extrapolated magnetic topology, it is suggested that the magnetic reconnection site may move southward by approximately 20 Mm until it reaches a region where the open magnetic field lines are oriented north–south. [ABSTRACT FROM AUTHOR]

Aims. Solar radio type II bursts are often associated with coronal shocks driven by solar eruptions. In this study, we report a type II burst associated with filament–filament interaction. Methods. Combining the high-quality multiwavelength observations from CHASE, SDO, STEREO, and CALLISTO, we conducted a detailed study of the type II burst associated with filament–filament interaction. Results. On 2023 September 11, an erupting filament (F1) likely disturbed a nearby long filament (F2), causing F2 to subsequently erupt. As a result of possible magnetic reconnection between ejective materials from the two filaments, loop-like structures formed perpendicular to them. Subsequently, the expansion of these loop-like structures triggered a strong coronal mass ejection (CME). Interestingly, a type II burst appeared on the solar spectrum around the time when the loop-like structures formed and the CME appeared above the occulting disk of STEREO/COR1. By converting the frequency of the type II burst to the coronal height using polarization brightness data recorded by the COR1 coronagraph and the spherically symmetric polynomial approximation technique, we determined the formation height of the type II burst to be around 1.45 R⊙, with a speed of approximately 440 km s−1. This is comparable to the observed height of the CME (∼1.43 R⊙), although slightly lower in speed (540 km s−1). Conclusions. All these results indicate that the type II burst was closely associated with filament–filament interactions and was possibly excited by the accompanying CME at the flank. We suggest that the filament–filament interactions played an important role in producing the type II burst by acting as a piston to trigger a strong CME. [ABSTRACT FROM AUTHOR]

In the two-dimensional framework of compressible resistive MHD, we examine the effect of localized plasma flow on the evolution of plasmoids magnetic islands induced during magnetic reconnection with different values of velocity amplitude, ranging from sub-Alfv'enic to super-Alfv'enic levels. To better understand the influence of localized flow on plasmoid formation and the nonlinear evolution of the current sheet (known as plasmoid instability), we considered a wide range of velocity amplitudes and scale lengths of localized flow. The simulation results show that, by increasing the velocity amplitude from sub-Alfv'enic to super-Alfv'enic within a scale length smaller than the current sheet thickness, plasmoid instability (PI) is suppressed, and the initial structure of the current sheet is preserved. The growth rate of PI decreases as the localized flow thickness increases, indicating that the scale length of localized flow is a significant parameter in the magnetic reconnection process. The presence of localized plasma flow in the current layer causes a displacement of the initial magnetic reconnection site (primary X-point). Due to multiple reconnections in sub-Alfv'enic flows, the initial X-point movement velocity increases in the direction of the localized flow, while in super-Alfv'enic flows, the movement velocity of the initial X-point decreases, as magnetic reconnection does not occur. Thus, the growth rate of PI decreases with increasing localized flow velocity amplitude. [ABSTRACT FROM AUTHOR]

Oscillatory reconnection is a specific type of time-dependent reconnection which involves periodic changes in the magnetic topology of a null point. The mechanism has been reported for a variety of magnetic field strengths and configurations, background temperatures, and densities. All these studies report an oscillation in the current density at the null point, but also report a variety of periods, amplitudes, and overall behaviors. We conduct a parametric study for equilibrium magnetic field strength and initial background temperature, solving two-dimensional resistive magnetohydrodynamic equations around a magnetic X-point. We introduce a parameter space for the ratio of internal to magnetic energy and find self-similar solutions for simulations where this ratio is below 0.1 (which represents a magnetically dominated environment or, equivalently, a low-beta plasma). Self-similarity can be seen in oscillations in the current density at the null (including amplitude and period), ohmic heating, and the temperature generated via reconnection jets. The parameter space of energy ratios also allows us to contextualize previous studies of the oscillatory reconnection mechanism and bring those different studies together into a single unified understanding. [ABSTRACT FROM AUTHOR]

The document "Solar Radio Emissions" discusses the wide frequency range of radio emissions from the Sun, originating from different layers of the solar atmosphere and produced by various physical processes. It highlights the importance of solar radio observations in diagnosing magnetic fields, detecting energetic particle acceleration, and predicting space weather events. The document also introduces recent advancements in solar radio telescopes and presents research papers on topics such as solar radio bursts, quasi-periodic pulsations, and the classification of solar radio spectra. Additionally, it explores the potential of using radio detectors to search for ultralight dark matter conversions in the solar corona and solar wind plasmas. [Extracted from the article]

The study aims to understand the role of solar wind current sheets (CSs) in shaping the spectrum of turbulent fluctuations and driving dissipation processes in space plasma. Local non-adiabatic heating and acceleration of charged particles in the solar wind is one of the most intriguing challenges in space physics. Leading theories attribute these effects to turbulent heating, often associated with magnetic reconnection at small-scale coherent structures in the solar wind, such as CSs and flux ropes. We identify CSs observed at 1 AU in different types of the solar wind around and within an interplanetary coronal mass ejection (ICME) and analyze the corresponding characteristics of the turbulent cascade. It is found that the spectra of fluctuations of the interplanetary magnetic field may be reshaped due to the CS impact potentially leading to local disruptions in energy transfer along the cascade of turbulent fluctuations. Case studies of the spectra behavior at the peak of the CS number show their steepening at MHD scales, flattening at kinetic scales, and merging of the spectra into a single form, with the break almost disappearing. In the broader vicinity of the CS number peak, the behavior of spectral parameters changes sharply, but not always following the same pattern. The statistical analysis shows a clear correlation between the break frequency and the CS number. These results are consistent with the picture of turbulent reconnection at CSs. The CS occurrence is found to be statistically linked with the increased temperature. In the ICME sheath, there are two CS populations observed in the hottest and coldest plasma. [ABSTRACT FROM AUTHOR]

Magnetic reconnection is an important process, ubiquitous in space and in laboratory magnetized plasmas. In a tokamak device, helical magnetic field perturbations "tear" the axisymmetric equilibriun configuration growing exponentially on a "tearing" time scale and subsequently evolve into a magnetic island which saturates at a width which produces a minimum in the magnetic energy of the configuration. Large magnetic island may lead to disruptive collapse of the discharge, through phases of thermal quench and current quench.A reliable tokamak reactor operation,on the economically useful time scales, requires the development of strategies to keep under control, and suppress the nonlinear islands growth to avoid disruptions. Here we summarize the state of the art of the problem and of the proposed solutions. [ABSTRACT FROM AUTHOR]

In the dynamic and complex environment of the solar corona, the interaction between kinetic Alfvén waves (KAWs) and magnetic null points might play a significant role in understanding various plasma processes. Recognizing the potential role of reconnection in coronal heating, our study aims to delve into how different types of null points affect KAW dynamics and ultimately contribute to heating. We investigate the behavior of nonlinear KAWs near the more frequently occurring components-null point with a mean magnetic field in the solar corona. The nonlinearity is attributed to the ponderomotive effects due to density perturbations. We used a three-dimensional model equation that describes the dynamics of KAWs in the presence of components-null point. Numerical methods are employed to solve the model equation for solar coronal parameters. Our simulations reveal that the nonlinear interaction between KAWs and magnetic null points can lead to the generation and amplification of turbulent and chaotic structures. This formation of localized structures, progressively exhibit more chaotic behavior over time, which may efficiently contribute to energy transfer. The power spectrum analysis of these turbulent structures shows a steeper spectrum with a pronounced cascade. Turbulence implies the presence of localized plasma heating, particle acceleration, and magnetic reconnection. These phenomena have significant implications for understanding the energy transport, particle dynamics, and magnetic topology in the solar corona. We also address nonlinearity's role in promoting turbulence. This research offers insights into the dynamics of nonlinear KAWs near null points in the solar corona, suggesting their potential role in energy transfer and current sheet formation. [ABSTRACT FROM AUTHOR]

Spider pulsars are compact binary systems composed of a millisecond pulsar and a low-mass companion. Their X-ray emission – modulated on the orbital period – is interpreted as synchrotron radiation from high-energy electrons accelerated at the intrabinary shock. We perform global two-dimensional particle-in-cell simulations of the intrabinary shock, assuming that the shock wraps around the companion star. When the pulsar spin axis is nearly aligned with the orbital angular momentum, we find that the magnetic energy of the relativistic pulsar wind – composed of magnetic stripes of alternating field polarity – efficiently converts to particle energy at the intrabinary shock, via shock-driven reconnection. The highest energy particles accelerated by reconnection can stream ahead of the shock and be further accelerated by the upstream motional electric field. In the downstream, further energization is governed by stochastic interactions with the plasmoids/magnetic islands generated by reconnection. We also extend our earlier work by performing simulations that have a larger (and more realistic) companion size and a more strongly magnetized pulsar wind. We confirm that our first-principles synchrotron spectra and light curves are in good agreement with X-ray observations. [ABSTRACT FROM AUTHOR]

The tailward high‐speed flows, in which various kinetic processes and magnetic structures can be embedded, are usually produced by the magnetic reconnection in the Earth's magnetotail. Here, using high‐resolution measurements from the Magnetospheric Multiscale (MMS) mission, we report an intense current in the tailward high‐speed flow. The current density can reach ∼180 nA/m2 and is primarily carried by electrons. Taking advantage of the First‐Order Taylor Expansion (FOTE) method, we reveal that such an intense current is associated with a ribbon‐like magnetic structure. A large electric field, reaching ∼90 mV/m, is also observed at the magnetic structure. The Hall term dominates the electric field, however, the contribution from the pressure gradient term and the electron inertial term is nonnegligible and can lead to strong energy conversion (E ⋅ J > 2 nW/m3) through the synergistic action with the intense current. This study improves the understanding of the current behaviors and energy conversion associated with magnetic structures in the Earth's magnetotail. Plain Language Summary: As products of the magnetotail magnetic reconnection, the earthward and tailward high‐speed flows can be usually observed as associated with a variety of kinetic processes and magnetic structures. Here, for the first time, we report an electron‐carried intense current associated with a ribbon‐like magnetic structure in the tailward high‐speed flow, by using high‐resolution MMS data and the First‐Order Taylor Expansion (FOTE) method. Encountering a large electric field with a nonnegligible contribution from the pressure gradient term and electron inertial term, such intense current leads to a strong energy conversion at the ribbon‐like magnetic structure. This study shed light on how the intense current is associated with the ribbon‐like magnetic structure and how the strong energy conversion is driven at such a structure, which complements the knowledge of the energy conversion process in the Earth's magnetotail. Key Points: An electron‐carried intense current (J > 180 nA/m2) is observed in association with a ribbon‐like structure in the tailward high‐speed flowA large electric field, with nonnegligible contribution from pressure gradient and electron inertial term, is observed at such a structureThe intense current and large electric field work together to drive a strong energy conversion (E ⋅ J > 2 nW/m3) at this structure [ABSTRACT FROM AUTHOR]

Starting in the evening of 10 May 2024 the Earth's magnetosphere was hit by the coronal mass ejections (CMEs) creating the largest geomagnetic storm in ∼ ${\sim} $20 years. The CME encounter was characterized by variations of plasma number density and magnetic field. Here, I present the ARTEMIS observations at the lunar orbit during this event. The IMF bz ${b}_{z}$ ranged from −60 to +40 nT both with ∼ ${\sim} $hour to minutes periodicity with plasma jets propagating in ±zGSE $\pm {z}_{\mathit{GSE}}$‐direction within multi‐scale wave structures. Similar signature has been recently reported at the magnetopause by MMS spacecraft (Li et al., 2023, https://doi.org/10.1029/2023GL105539; Nykyri, 2024, https://doi.org/10.1029/2024GL108605) during a strongly southward IMF. Here, I show that the CME boundaries were KH unstable leading to multi‐scale density and magnetic field fluctuations including reconnection jets. The wavelengths varied from ∼ ${\sim} $60 to 270 RE ${R}_{E}$, suggesting that the magnetosphere was periodically exposed to successive intervals of strongly northward and southward IMF leading to enhanced mass and magnetic flux loading. Plain Language Summary: Coronal mass ejections (CMEs) are giant explosions of plasma and magnetic field from the Sun which can produce beautiful Auroras, but also destroy our satellites, power delivery networks, and avionics systems. The seriousness of the storm depends on the pre‐existing conditions of the magnetosphere, the strength and orientation of the magnetic field within the CME structure, its size and speed which drives its duration, as well as the properties of the plasma within it. In this paper, I discuss and analyze the CME observations during the recent Mother's day storm (started on 10 May 2024) using the ARTEMIS spacecraft data at the lunar orbit. During the CME encounter, the SC were exposed to periodic north‐south‐variations of the magnetic field orientation and plasma density which allowed the Earth's magnetosphere to be successively filled with plasma, and magnetic flux likely enabling its effective acceleration in large‐quantities. I show that these periodic variations were produced by giant ∼ ${\sim} $ 60–270 RE ${R}_{E}$ waves at the boundary of the CMEs, such that the entire Earth's magnetosphere was surfing the crests and troughs of these waves, and absorbing the kinetic and magnetic energy from the solar wind. Key Points: Velocity shear at the boundary of a coronal mass ejection (CME) ejecta created Kelvin‐Helmholtz Instability (KHI) ∼ ${\sim} $7 million km upstream the Earth‐Sun L‐1 pointKHI generated multi‐scale density and IMF bz ${b}_{z}$ fluctuations from −60 to +40 nT at the boundary layers of the CME ejecta encountersKH wavelengths varied from ∼ ${\sim} $60 to ∼ ${\sim} $270 RE ${R}_{E}$ implying periodic and successive mass and magnetic flux loading of the magnetosphere system [ABSTRACT FROM AUTHOR]