Reconnection Research Articles (Page 1)

Abstract On 2024 July 25, while observing the solar active region NOAA 13762 with the high-resolution 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory, we witnessed two mysterious phenomena: the partial detachment of filament strands from its main body in the chromosphere and the sudden disappearance of a sunspot penumbra in the photosphere, the former accompanied by small flares. Our analysis reveals a spatiotemporal correlation between the filament peeling process and the penumbral disappearance. To understand the above observations physically, we performed a magnetohydrodynamic simulation that successfully replicated the disappearance of the penumbra as a consequence of weakened horizontal magnetic field. The simulations demonstrate that both the filament peeling and the penumbral decay are driven by the same underlying process: the upward expansion of the magnetic flux rope induced by null point magnetic reconnection. These results suggest a novel mechanism by which the Sun sheds magnetic flux to interplanetary space in the form of filament peeling and penumbral disappearance.

Abstract Solar Orbiter conducted a series of flare-optimised observing campaigns in 2024 using the Major Flare Solar Orbiter Observing Plan (SOOP). Dedicated observations were performed during two distinct perihelia intervals in March/April and October, during which over 22 flares were observed, ranging from B- to M-class. These campaigns leveraged high-resolution and high-cadence observations from the mission’s remote-sensing suite, including the High-Resolution EUV Imager (EUI/HRI EUV ), the Spectrometer/Telescope for Imaging X-rays (STIX), the Spectral Imaging of the Coronal Environment (SPICE) spectrometer, and the High Resolution Telescope of the Polarimetric and Helioseismic Imager (PHI/HRT), as well as coordinated ground-based and Earth-orbiting observations. EUI/HRI EUV , operating in short-exposure modes, provided two-second-cadence, non-saturated EUV images, revealing structures and dynamics on scales not previously observed. Simultaneously, STIX captured hard X-ray imaging and spectroscopy of accelerated electrons, while SPICE acquired EUV slit spectroscopy to probe chromospheric and coronal responses. Together, these observations offer an unprecedented view of magnetic reconnection, energy release, particle acceleration, and plasma heating across a broad range of temperatures and spatial scales. These campaigns have generated a rich dataset that will be the subject of numerous future studies addressing Solar Orbiter’s top-level science goal: “How do solar eruptions produce energetic particle radiation that fills the heliosphere?” . This paper presents the scientific motivations, operational planning, and observational strategies behind the 2024 flare campaigns, along with initial insights into the observed flares. We also discuss lessons learned for optimizing future Solar Orbiter Major Flare campaigns and provide a resource for researchers aiming to utilize these unique observations.

Laboratory astrophysics is an emerging interdisciplinary field bridging high-energy-density plasma physics and astrophysics. Optical diagnostic techniques offer high spatiotemporal resolution and the unique capability for simultaneous multi-field measurements. These attributes make them indispensable for deciphering extreme plasma dynamics in laboratory astrophysics. This review systematically elaborates on the physical principles and inversion methodologies of key optical diagnostics, including Nomarski interferometry, shadowgraphy, and Faraday rotation. Highlighting frontier progress by our team, we showcase the application of these techniques in analyzing jet collimation mechanisms, turbulent magnetic reconnection, collisionless shocks, and particle acceleration. Future trajectories for optical diagnostic development are also discussed.

Abstract Understanding the mechanisms behind fast magnetic reconnection and subsequent plasma heating is essential to explain the temperatures of a few million kelvin observed in the solar corona. This study investigates the influence of initial current sheet width and stratification on the reconnection process and coronal temperature within a large-scale magnetohydrodynamics framework. Additionally, it further addresses the contribution of small- to large-scale dynamics through the Hall term. Using numerical simulations, we demonstrate that even modest reductions in the initial current sheet width significantly speed up the reconnection process, yielding faster rates of temperature rise and achieving high peak values without requiring external fluctuations. Moreover, introducing a dependence on scale height in the initial coronal magnetic field and density profiles enhances reconnection rates and temperature increases. We also observe earlier evolution of fast reconnection with narrower current sheets and shorter scale heights, resulting in a more frequent formation of magnetic islands and X-points that evolve dynamically over time. Under these initial settings, the Hall term’s curl is amplified by three orders of magnitude, reaching 1% of the characteristic scale required to influence large-scale dynamics and offering insight into the multiscale interactions essential for coronal heating processes. This study underscores the significance of minor adjustments in initial conditions for enhancing magnetic reconnection, coronal heating, and amplifying the Hall term’s influence on large-scale dynamics.

Abstract Low-frequency radio emission in the form of type II and III bursts is a direct indicator of plasma motion in the solar corona and interplanetary medium. However, detecting equivalent events on solar analogs requires thousands of observing hours and complementary multiwavelength observations to constrain the origin of the radio emission. To address this, we have begun the Study of Space Weather Around Young Suns (SWAYS), a multiwavelength program for monitoring space weather around young, solar-type stars. This program currently focuses on five solar-type stars spanning 100–800 Myr in age. It includes a dedicated observing scheme from the recently upgraded Owens Valley Radio Observatory (OVRO) Long Wavelength Array (LWA) operating at 13–86 MHz to search for stellar analogs of solar type II and III bursts. We have built the optical photometry instrument Flarescope to operate simultaneously with OVRO-LWA observations to investigate whether radio bursts are accompanied by magnetic reconnection events. We analyze the performance based on a 1 hr observation of π 1 UMa, which shows that Flarescope can reach submillimagnitude precision through nondifferential photometry on π 1 UMa in 60 s integration times when diffusing the light with engineered diffusers. A small field of OVRO-LWA cross-correlated data centered on π 1 UMa reaches a noise level of 740 mJy at 10 s integration time, consistent with confusion noise. With this precision, we should be able to detect large optical flares and related radio bursts that may indicate accompanying coronal mass ejections and energetic particle events. In this paper, we present the design, framework, and performance of the SWAYS program.

Abstract The quiescent or dynamic nature of fine-scale raylike features in the Sun corona, observed in visible light, is still an open question. Here, we show that most of the daily and hourly periodic variations in visible light brightness of the high corona (up to 15 R ⊙ ) are aligned to the tip of streamers and are consistent with the periodicity of plasma release from simulations of tearing-induced magnetic reconnection at the heliospheric current sheet. The areas in which we detect periodicities can be used as tracers of nonquiescent fine coronal rays. This also allows their distinction from coronal rays more likely to be real quiescent features or associated with smaller and/or faster unresolved brightness variations. In the low- and middle-corona (down to 1.4 R ⊙ ) similar brightness variations are observed along loop-like and cusp-like features marking boundaries of streamers, which then connect to radial features in the high corona. This suggests the presence of additional mechanisms in the low- and middle-corona periodically releasing density structures in the solar wind. The periodicity distributions show a solar cycle modulation with shorter periods (smaller structures) during solar maximum. Periodicities are observed within streamers during solar minimum but are visible at all latitudes, even extending radially from the poles, during solar maximum.

Abstract In this paper, we report multiwavelength and multipoint observations of the prominence eruption originating from active region 11163, which generated an M3.5 class flare and a coronal mass ejection (CME) on 2011 February 24. The prominence lifts off and propagates nonradially in the southeast direction. Using the revised cone model, we carry out three-dimensional reconstructions of the ice-cream-like prominence. It is found that the latitudinal inclination angle decreases from ∼60° to ∼37°, indicating that the prominence tends to propagate more radially. The longitudinal inclination angle almost keeps constant (−6°). The highly inclined prominence eruption and the related CME drive an extreme-ultraviolet (EUV) wave, which propagates southward at speeds of ∼381.60 and ∼398.59 km s −1 observed in 193 and 304 Å, respectively. The M3.5 class flare presents quasiperiodic pulsations (QPPs) in soft X-ray, hard X-ray, EUV, and radio wavelengths with periods of 80−120 s. Contemporary with the flare QPPs, a thin current sheet and multiple plasmoids are observed following the eruptive prominence. Combining with the appearance of drifting pulsation structure, the QPPs are most probably generated by quasiperiodic magnetic reconnection and particle accelerations as a result of plasmoids in the current sheet.

Magnetic reconnection, often accompanied by a turbulence interaction, is a ubiquitous phenomenon in astrophysical environments. However, the current understanding of the nature of turbulent magnetic reconnection remains insufficient. We investigate the statistical properties of reconnection turbulence in the framework of the self-driven reconnection. Using the open-source software package AMUN, we first performed numerical simulations of turbulent magnetic reconnection. We then obtained the statistical results of reconnection turbulence by traditional statistical methods such as the power spectrum and structure function. Our numerical results demonstrate: (1) the velocity spectrum of reconnection turbulence follows the classical Kolmogorov type of E∝ k^ while the magnetic field spectrum is steeper than the Kolmogorov spectrum, which are independent of limited resistivity, guide field, and isothermal or adiabatic fluid states; (2) most of the simulations show the anisotropy cascade, except that the presence of a guide field leads to an isotropic cascade; (3) reconnection turbulence is incompressible in the adiabatic state, with energy distribution being dominated by the velocity solenoidal component; and (4) different from pure magnetohydrodynamic (MHD) turbulence, the intermittency of the velocity field is stronger than that of the magnetic field in reconnection turbulence. The steep magnetic field spectrum, together with the velocity spectrum of a Kolmogorov type, can characterize the feature of the reconnection turbulence. In the case of the presence of the guide field, the isotropy of the reconnection turbulence cascade is also different from the cascade mode of pure MHD turbulence. Our experimental results provide new insights into the properties of reconnection turbulence, which will contribute to advancing self-driven reconnection theory.

Vortex–magnetic interactions shape magnetohydrodynamic (MHD) turbulence, influencing energy transfer in astrophysical, geophysical and industrial systems. In the solar atmosphere, granular-scale vortex flows couple strongly with magnetic fields, channelling energy into the corona. At high Reynolds numbers, vorticity and magnetic fields are nearly frozen into the charged fluid, and MHD flows emerge from the Lorentz force mediated interactions between coherent vortex structures in matter and the field. To probe this competition in a controlled setting, we revisit the canonical problem of two antiparallel flux tubes. By varying the magnetic flux threading each tube – and thus sweeping the interaction parameter $N_i$ , which gauges Lorentz-to-inertial force balance – we uncover three distinct regimes: vortex-dominated joint reconnection, instability-triggered cascade, and Lorentz-induced vortex disruption. At low $N_i$ , classical vortex dynamics dominates, driving joint vortex–magnetic reconnection, and amplifying magnetic energy via a dynamo effect. At moderate $N_i$ , the system oscillates between vorticity-driven attraction and magnetic damping, triggering instabilities and nonlinear interactions that spawn secondary filaments and drive an energy cascade. At high $N_i$ , Lorentz forces suppress vortex interactions, aligning the tubes axially while disrupting vortex cores and rapidly converting magnetic to kinetic energy. These findings reveal how the inertial–Lorentz balance governs energy transfer and coherent structure formation in MHD turbulence, offering insight into vortex–magnetic co-evolution in astrophysical plasmas.

Electrostatic Field Formed by Charge Separation in Magnetic Reconnection with a Guide Field

Abstract Magnetic reconnection is an important driving mechanism of many chromospheric phenomena, e.g., UV bursts and chromospheric jets. Information about magnetic fields is indispensable for analyzing chromospheric magnetic reconnection, which is mainly encoded in polarization signals. The purpose of this work is to predict possible Stokes features related to chromospheric reconnection events, from realistic two-dimensional magnetohydrodynamic simulation and Stokes profile synthesis. An emerging magnetic flux sheet is imposed at the bottom boundary of a well-relaxed unipolar atmosphere that spans from the upper convection zone to the corona. The reconnection region is heated to ∼7 kK and the outflow velocity reaches up to ∼35 km s −1 . Through Stokes profile synthesis, several Stokes features related to reconnections and plasmoids are reproduced. We found sign reversal features on circular polarization and amplitude reduction features on linear polarization at reconnection sites. Also, we report strong linear and circular polarization signals corresponding to huge (∼300 km) and tiny (∼40 km) plasmoids, respectively. We conclude that both linear and circular polarization signals may reveal the distinctive physical mechanisms in reconnections and enhance our understanding of magnetic reconnection in observations.

Abstract We present a multiwavelength observational investigation of filaments and coronal loop interactions in active region NOAA 13229 during 2023 February 21–23. Our findings demonstrate that a series of interactions between filaments (F1 and F2), coronal loops, and the loop–filament system, mediated by reconnection with overlying hot coronal loops, led to the formation of a longer inverse S-shaped filament. Key mechanisms, including flux convergence, cancellation, and submergence along the polarity inversion line, drive these interactions. Photospheric horizontal plasma flows and the transverse component of the Lorentz force may facilitate footpoint convergence, enabling magnetic reconnection and structural reorganization. The nonlinear force-free field extrapolations indicate that magnetic reconnections likely occur at the interface of loop–loop or filament–loop that drive the formation of large-scale filament systems.

Abstract The outward transport of plasma and magnetic fluxes in the gas giant magnetospheres is balanced with a return flow of flux tubes emptied through magnetic reconnection. Evidence of interchange motions between inward and outward moving flux tubes have long been reported around Jupiter and Saturn. Although amply documented at Saturn, the lack of useable low energy plasma data has prevented the analysis of their plasma properties at Jupiter. The Juno data sets allow us to characterize the plasma populations inside nine interchange events at Jupiter between M‐shells 5 and 10. We confirm that they are strongly depleted in heavy ions and low energy protons and electrons, but filled with higher energy protons and electrons. We model the pitch‐angle distribution of trapped electrons through adiabatic transport and estimate that the reported flux tubes were likely isotropic between M‐shells 11 and 35. The observed features bear strong similarities with their Kronian counterparts.

Abstract The interplanetary magnetic field (IMF) that pervades the Solar System interacts with the planetary magnetospheres via the process of magnetic reconnection. Reconnection that causes the dominant energy transfer into Earth’s magnetosphere is most efficient when the IMF is directed southward. The only existing, simplified model of the seasonal variations of the southward component of IMF (Bs) was constructed in 1973. Since then, as far as we know, the realistic model of Bs has not been developed although for more than 60 years the IMF observations have been available that could be used to construct and test the new model. Here we demonstrate the mathematical formalism to model seasonal variations of Bs and Bs ordered according to the IMF polarity considering the real situation in which the IMF fluctuates about the Parker spiral direction and changes through the solar cycles. The derived quantitative model of the seasonal variations of Bs (EBV model) can completely reproduce all the main features of the measured Bs, its absolute value and solar cycle variation. It opens a way to quantify, for the first time, the relation between the seasonal variations of magnetospheric quantities and Bs. By clarifying the origin and characteristics of Bs, we may be better able to understand the importance of the magnetic reconnection process for structuring the magnetosphere of the Earth and other planets and the role it has in modulating magnetospheric activities.

Abstract High energy electron bunches from the laser-driven relativistic magnetic reconnection has been intensively studied. However, diagnostic methods for identifying such acceleration mechanism remain inadequate. This study utilizes 2.5-dimensional Particle-In-Cell simulations to explore a diagnostic approach based on electron polarization dynamics governed by the Thomas-Bargmann-Michel-Telegdi equation. The trajectories of electrons accelerated by the MR are confined in the current sheet, where the magnetic field is effectively annihilated. The resulting electron beam exhibits extremely low depolarization, distinguishing it from other accelerated populations and serving as a definitive signature of magnetic reconnection. This diagnostic approach enables more detailed investigations of magnetic reconnection-driven acceleration mechanisms in future studies.

Abstract Flux ropes (FRs), ubiquitous helical magnetic structures in solar system plasmas, are important to energy and particle transport. At Mars, where global intrinsic magnetic fields are absent, FRs form through magnetic reconnection (MR) and magnetospheric or ionospheric boundary wave instabilities (BWIs), but their role in ion escape remains controversial. Here, we first present the global distribution of MR‐ and BWI‐FRs from Martian ionosphere to magnetosheath, utilizing 4,012 FR events identified from 5‐year observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. We find that the global occurrence rate of FRs associated with BWIs is comparable with those from MR. Enhanced oxygen ion outflow fluxes and densities within most nightside BWI‐FRs suggest they predominantly originate from the dayside ionosphere/magnetosphere. These BWI‐FRs have sufficient magnetic field intensity to carry oxygen ions beyond escape energies, suggesting their potential role in facilitating global ion escape from Mars via magnetotail transport.

Abstract Magnetic reconnection explosively converts magnetic energy into plasma heating and particle acceleration. At Earth's magnetopause, reconnection governs solar wind‐magnetosphere coupling and drives global convection. Understanding these processes requires resolving reconnection's spatiotemporal evolution, which is difficult for in situ observations but achievable in laboratory experiments. However, building a geometry like the real magnetopause in laboratory remains a key challenge. Here, we present the first laboratory experiment at the Space Plasma Environment Research Facility trying to replicates Earth's magnetopause configuration. Using a dipole magnet (mimicking magnetosphere) and coaxial flux cores (simulating solar wind), we establish a magnetopause‐like current sheet via dynamic plasma compression. Measured Hall magnetic fields confirm Hall reconnection, transitioning from an asymmetric multiple x ‐lines state to a symmetric single x ‐line state. This dynamic evolution will impact global energy conversion and transport at magnetopause.

Abstract Plasma waves can initiate, regulate, or reflect magnetic reconnection efficiently converting magnetic energy into plasma energy. While waves ranging from below the ion cyclotron frequency to above the electron plasma frequency are commonly observed near reconnection sites, electromagnetic ion cyclotron (EMIC) waves—frequent in other plasma environments—have been rarely observed in the reconnection region. Here, we report the first detection of EMIC waves in a magnetic reconnection exhaust at Earth's magnetopause. The free energy required for EMIC wave growth was supplied by the strong perpendicular‐to‐parallel temperature anisotropy of hot proton beams. This proton temperature anisotropy was generated by magnetopause reconnection, rather than inherited from the magnetosheath. Our findings differ from previous reports of parallel‐preferential proton heating during magnetopause reconnection, calling for revised theoretical frameworks to reconcile observed perpendicular‐preferential heating with established reconnection paradigms.

Abstract We study electron energization in turbulence-generated current sheets in the shock transition region by means of fully kinetic collisionless plasma simulations and theory. Using parameters in the Earth’s bow shock, we perform a two-dimensional particle-in-cell simulation of a quasi-parallel shock. In shock turbulence, many current sheets are produced, including those exhibiting magnetic reconnection and those that are not reconnecting. The electron temperature is enhanced in nonreconnecting current sheets as well as in reconnecting current sheets and magnetic islands. Performing electron trajectory tracing analysis, we find that energetic electrons are produced in nonreconnecting thinning current sheets. The motional electric field during the thinning process of a current sheet energizes both magnetized and unmagnetized electrons. We analytically show that the energization rate for unmagnetized electrons is slightly less than that of adiabatic energization for magnetized electrons, but unmagnetized electrons can be effectively trapped in magnetic field structures formed in thinning current sheets and continue to be energized. These nonreconnecting current sheets produce energetic electrons whose energies are comparable to the energetic electrons produced in magnetic islands, and they can reach the injection energy for diffusive shock acceleration, which is an acceleration mechanism for producing cosmic rays. The number of electrons that are energized in nonreconnecting current sheets is about a quarter of that in reconnection regions. The energization mechanism can be applicable to various space and astrophysical environments, including planetary bow shocks and supernova remnant shocks.

Abstract By analyzing continuous Magnetospheric Multiscale observations at the magnetopause boundary layer, combining both magnetohydrodynamic and kinetic signatures, we have successfully captured dynamic magnetic reconnection processes in exceptional detail. Our results demonstrate that magnetic reconnection exhibits rapid transitions between distinct operational modes, characterized by: (a) primary single X‐line reconnection punctuated by intermittent secondary reconnection, leading to large‐scale multiple X‐line formations; (b) stable single X‐line reconnection with oscillating X‐line positions; (c) rapid switching of reconnection X‐lines between opposite sides of the spacecraft; and (d) transient suppression occurring during otherwise steady reconnection periods. These observations provide definitive evidence for the inherently dynamic and intermittent behavior of magnetopause reconnection, revealing its capacity for swift configuration changes under varying conditions.