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Solar pores are transient dark spots in the continuum images of the Sun. Their dynamics are closely associated with solar magnetic fields and plasma motion. Their motions have been found to be correlated with their magnetic pressure differences. This work is aimed to investigate possible reasons for this correlation. Our examination of 19 pairs of bipolar pores reveals a magnetic pressure difference rule between the pores of a same pair: their signs of the differences between the magnetic pressures at the front and back sides are always opposite, and their directions of the maximum positive difference between the magnetic pressures at the opposite ends are always both pointing toward the left or right and are always slightly toward the higher latitudes. The rule indicates that the properties of the bipolar pores are influenced by the solar global magnetic fields and rotation.

New emerging flux (NEF) has long been considered a mechanism for solar eruptions, but the detailed process remains an open question. In this work, we explore how NEF drives a coronal magnetic configuration to erupt. This configuration is created by two magnetic sources of strengths M and S embedded in the photosphere, one electric-current-carrying flux rope (FR) floating in the corona, and an electric current induced on the photospheric surface by the FR. The source M is fixed, accounting for the initial background field, and S changes, playing the role of NEF. We introduce the channel function C to forecast the overall evolutionary behavior of the configuration. The location, polarity, and strength of NEF govern the evolutionary behavior of the FR before eruption. In the case of ∣ S / M ∣ < 1, with reconnection occurring between new and old fields, the configuration in equilibrium evolves to the critical state, invoking the catastrophe. In this case, if the polarities of the new and old fields are opposite, reconnection occurs as NEF is close to the FR, and if the polarities are the same, reconnection happens as NEF appears far from the FR. With different combinations of the relative polarity and the location, the evolutionary behavior of the system gets complex, and the catastrophe may not occur. If ∣ S / M ∣ > 1 and the two fields have opposite polarity, the catastrophe always takes place, but if the polarities are the same, the catastrophe occurs only as NEF is located far from the FR; otherwise, the evolution ends up either with a failed eruption or without a catastrophe at all.

In this Letter, we examine the relationship between 3D magnetic free energy (MFE) and flaring activity using 83 major solar flares (M-class and X-class) in nine solar active regions (ARs). For this, we use 998 nonlinear force-free field extrapolations compiled by the “Institute for Space-Earth Environmental Research Database” at Nagoya University. These ARs produced at least three major flares with distinct rising and peak phases of 3D MFE. For each phase, the solar flare occurrence rate (FOR) is calculated as a ratio of the number of flares to the duration. The major results from this study are summarized as follows. First, there is no clear linear correlation (CC = 0.15) between 3D MFE and flare peak flux. Second, the FOR (3.4 day ^−1 ) of the rising phase is a little higher than that (3.1 day ^−1 ) of the peak phase, depending on AR. Third, for several flares, there are noticeable decreases in 3D MFE, which correspond to the typical energy of a major flare (about 10 ^32 erg). Fourth, it is interesting to note that there are noticeable enhancements in FORs at several local maxima of 3D MFE, which may be associated with flux emergence and/or shearing motions. Fifth, the flare index rates, which are defined as the summation of flaring activity divided by the duration, of rising and peak phases are 151 day ^−1 and 314 day ^−1 , respectively. Our results imply that the traditional and simple “storage and release” model does not apply to flare activities, and the random perturbation may be important for triggering flares.

Fan-spine magnetic structure, as a fundamental three-dimensional topology in magnetic reconnection theory, plays a crucial role in producing solar jets. However, how fan-spine configurations form in the solar atmosphere remains elusive. Using the Chinese H α Solar Explorer (CHASE) and the Solar Dynamics Observatory, we present a case study on the complete buildup of fan-spine topology driven by flux emergence and the subsequent jet production. Two fan-spine structures and the two associated null points are present. Variations in null-point heights and locations were tracked over time during flux emergence. The north fan-spine structure is found to be created through magnetic reconnection between the newly emerged flux and the background field. Gentle reconnection persistently occurs after formation of the north fan-spine structure, resulting in weak plasma outflows. Subsequently, as flux emergence and magnetic helicity injection continue, the formation and eruption of minifilaments after reconnection at the quasi-separatrix layer between the two nulls trigger three homologous jets. The CHASE observations reveal that the circular flare ribbon, inner bright patch, and remote brightening all exhibit redshifted signatures during these jet ejections. This work unveils the key role of flux emergence in the formation of fan-spine topology, and highlights the importance of minifilaments for subsequent jet production.

The process of the Sun’s polar field cancellation reversal commences with the emergence of new cycle Hale’s polarity active regions. Once the Sun undergoes polarity reversal, typically occurring near the peak of solar activity, it begins the process of accumulating the seed field for the forthcoming solar cycle. In recent years, the advective flux transport (AFT) model has proven highly effective in forecasting the progression of polar fields by leveraging observations of surface flows and magnetic flux emergence. In this study, we make use of the predictive capability of the AFT model to simulate the evolution of the polar fields and estimate the timing of the Solar Cycle 25 polarity reversal in both hemispheres of the Sun. We use the statistical properties of active regions along with Solar Cycle 13, which closely resembles the current solar cycle (Cycle 25), to generate synthetic active regions in order to simulate future magnetic flux emergence in AFT to predict the evolution of the polar field. Based on our simulations, we anticipate that the northern hemisphere of the Sun will undergo a polarity reversal between 2024 June and November, with the center of our distribution at 2024 August. In the southern hemisphere, we anticipate a polarity reversal between 2024 November and 2025 July, centered around 2025 February. Additionally, assuming that the reversal of the axial dipole moment coincides with the peak of the solar cycle, our findings indicate that Cycle 25 is expected to peak in 2024 (likely between 2024 April and August).

We have performed 3D numerical simulations to investigate the effect of partial ionization on the process of magnetic flux emergence. In our study, we have modified the single-fluid MHD equations to include the presence of neutrals and have performed two basic experiments: one that assumes a fully ionized plasma (FI case) and one that assumes a partially ionized plasma (PI case). We find that the PI case brings less dense plasma to and above the solar surface. Furthermore, we find that partial ionization alters the emerging magnetic field structure, leading to a different shape of the polarities in the emerged bipolar regions compared to the FI case. The amount of emerging flux into the solar atmosphere is larger in the PI case, which has the same initial plasma beta as the FI case, but a larger initial magnetic field strength. The expansion of the field above the photosphere occurs relatively earlier in the PI case, and we confirm that the inclusion of partial ionization reduces cooling due to adiabatic expansion. However, it does not appear to work as a heating mechanism for the atmospheric plasma. The performance of these experiments in three dimensions shows that PI does not prevent the formation of unstable magnetic structures, which erupt into the outer solar atmosphere. [ABSTRACT FROM AUTHOR]

We investigate deviations in the mean phase travel time of acoustic waves preceding the emergence of 46 large active regions observed by the Helioseismic and Magnetic Imager. In our investigation, we consider two different procedures for obtaining the mean phase travel time, by minimizing the difference between cross-correlations and a reference, as well as the Gabor wavelet fitting procedure. We cross-correlate the time series of mean phase travel time deviations with the surface magnetic field and determine the peak correlation time lag. We also compute the perturbation index—the area integrated mean phase travel time deviations exceeding quiet Sun thresholds—and compare the time of peak perturbation index with the correlation time lag. We find that the lag times derived from the difference minimization procedure precede the flux emergence for 36 of the 46 active regions, and that this lag time has a noticeable correlation with the maximum flux rate. However, only 28 of the active regions have peak perturbation index times in the range of 24–48 hr prior to the flux emergence. Additionally, we examine the relationship between the properties of the emerged active regions and the strength of helioseismic signals prior to their emergence. [ABSTRACT FROM AUTHOR]

Besides a dense coverage of their high latitudes by starspots, rapidly rotating cool stars also display low-latitude spots in Doppler images, although generally with lower coverage. In contrast, flux emergence models of fast-rotating stars predict strong poleward deflection of radially rising magnetic flux as the Coriolis effect dominates over buoyancy, leaving a spot-free band around the equator. To resolve this discrepancy, we consider a flux tube near the base of the convection zone in a solar-type star rotating 8 times faster than the Sun, assuming field intensification by weak-tube explosions. For the intensification to continue into the buoyancy-dominated regime, the upper convection zone must have a significantly steeper temperature gradient than in the Sun by a factor that is comparable with that found in 3D simulations of rotating convection. Within the hypothesis that stellar active regions stem from the base of the convection zone, flux emergence between the equator and 20° latitudes requires highly supercritical field strengths of up to 500 kG in rapidly rotating stars. These field strengths require explosions of 100 kG tubes within the convection zone, compatible with reasonable values of the superadiabatic temperature gradient associated with the more rapid rotation.

Solar energetic events are caused by the release of magnetic energy accumulated in the solar atmosphere. To understand their initiating physical mechanisms, the dynamics of the coronal magnetic fields must be studied. Unfortunately, the dominant mechanisms are still unclear due to a lack of direct measurements. Numerical simulations based on magnetohydrodynamics (MHD) can reproduce the dynamical evolution of solar coronal magnetic field, providing a useful tool to explore flare initiation. Data-driven MHD simulations, in which the time-series observational data of the photospheric magnetic field is used as the simulation boundary condition, can explore different mechanisms. To investigate the accumulation of free magnetic energy through a solar eruption, we simulated the first of several large flares in NOAA active region 11283. We used a data-driven model that was governed by zero-beta MHD, focusing on the free magnetic energy accumulation prior to the M5.3 flare (2011 September 6 at 01:59 UT). We reproduced the flare-associated eruption following the formation of twisted magnetic fields, or a magnetic flux rope (MFR), formed by photospheric motions at its footpoints. We found that the eruption was first triggered by the growth of the torus instability. The erupting MFR caused magnetic reconnections with neighboring magnetic field lines located along the direction of the eruption. Using the simulation results and an axial-radial decay index centered on the MFR, we find a natural explanation for the inclination of the eruption and a possible approach to predict the direction of solar eruptive events.

As a relatively active region, the ephemeral region (ER) exhibits a highly complex pattern of magnetic flux emergence. We aim to study in detail the secondary flux emergences (SFEs), which we define as bipoles that appear close to ERs and finally coalesce with ERs after a period of time. We study SFEs during the whole process, from the emergence to the decay of five ERs observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. The maximum unsigned magnetic flux for each ER is around 10 ^20 Mx. Each ER has tens of SFEs with an average emerging magnetic flux of approximately 5 × 10 ^18 Mx. The frequency of normalized magnetic flux for all the SFEs follows a power-law distribution with an index of −2.08. The majority of SFEs occur between the positive and negative polarities of an ER, and their growth time is concentrated within 1 hr. The magnetic axis of SFE is found to exhibit a random distribution in the five ERs. We suggest that the relationship between SFEs and ERs can be understood by regarding the photospheric magnetic field observations as cross sections of an emerging magnetic structure. Tracking the evolution of ERs, we propose that these SFEs in ERs may have emerged consequentially from the bundle of flux tubes of ERs and that SFEs are partially emerged Ω-loops.

Magnetic flux emergence from the convection zone into the photosphere and beyond is a critical component of the behavior of large-scale solar magnetism. Flux rarely emerges amid field-free areas at the surface, but when it does, the interaction between the magnetism and plasma flows can be reliably explored. Prior ensemble studies have identified weak flows forming near emergence locations, but the low signal-to-noise ratio (S/N) required averaging over the entire data set, erasing information about variation across the sample. Here, we apply deep learning to achieve an improved S/N, enabling a case-by-case study. We find that these associated flows are dissimilar across instances of emergence and also occur frequently in the quiet convective background. Our analysis suggests the diminished influence of supergranular-scale convective flows and magnetic buoyancy on flux rise. Consistent with numerical evidence, we speculate that small-scale surface turbulence and/or deep convective processes play an outsized role in driving flux emergence.

Small-scale, newly emerging internetwork (IN) magnetic fields are considered a viable source of energy and mass for the solar chromosphere and possibly the corona. Multiple studies show that single events of flux emergence can indeed locally heat the low solar atmosphere through interactions of the upward propagating magnetic loops and the preexisting ambient field lines. However, the global impact of the newly emerging IN fields on the solar atmosphere is still unknown. In this paper, we study the spatiotemporal evolution of IN bipolar flux features and analyze their impact on the energetics and dynamics of the quiet-Sun atmosphere. We use high-resolution, multiwavelength, coordinated observations obtained with the Interface Region Imaging Spectrograph, Hinode, and the Solar Dynamics Observatory to identify emerging IN magnetic fields and follow their evolution. Our observational results suggest that only the largest IN bipoles are capable of heating locally the low solar atmosphere, while the global contribution of these bipoles appears to be marginal. However, the total number of bipoles detected and their impact estimated in this work is limited by the sensitivity level, spatial resolution, and duration of our observations. To detect smaller and weaker IN fields that would maintain the basal flux, and examine their contribution to the chromospheric heating, we will need higher resolution, higher sensitivity, and longer time series obtained with current and next-generation ground- and space-based telescopes.

Observations have shown a clear association of filament/prominence eruptions with the emergence of magnetic flux in or near filament channels. Magnetohydrodynamic (MHD) simulations have been employed to systematically study the conditions under which such eruptions occur. These simulations to date have modeled filament channels as 2D flux ropes or 3D uniformly sheared arcades. Here we present MHD simulations of flux emergence into a more realistic configuration consisting of a bipolar active region containing a line-tied 3D flux rope. We use the coronal flux-rope model of Titov et al. as the initial condition and drive our simulations by imposing boundary conditions extracted from a flux emergence simulation by Leake et al. We identify three mechanisms that determine the evolution of the system: (i) reconnection displacing footpoints of field lines overlying the coronal flux rope, (ii) changes of the ambient field due to the intrusion of new flux at the boundary, and (iii) interaction of the (axial) electric currents in the preexisting and newly emerging flux systems. The relative contributions and effects of these mechanisms depend on the properties of the preexisting and emerging flux systems. Here we focus on the location and orientation of the emerging flux relative to the coronal flux rope. Varying these parameters, we investigate under which conditions an eruption of the latter is triggered.

Solar pores are closely related to the concentration, dissipation, and transportation of solar magnetic flux. Their observable characteristics can provide constraints on models and simulations of magnetic flux emergence and formation. The specific property investigated in this study is their horizontal movement. The aim is to investigate whether the movement is correlated with any observable quantities. Our statistical analysis of 61 compact pores identified from the Spaceweather HMI Active Region Patches (SHARP) from 2011 to 2018 indicates that the direction of movement is often either parallel or antiparallel to the direction of maximum magnetic pressure difference (dP mag) at the opposite sides of the edges of the pores. The correlation coefficients for both the parallel and antiparallel cases are higher than 0.74. Despite the high correlation, our analysis using the transfer entropy indicates no significant causal relationship between the direction of motion and the direction of maximum dP mag. [ABSTRACT FROM AUTHOR]

We present observations and interpretation of a nonerupting filament in NOAA active region (AR) 12827 that undergoes splitting and restructuring on 2021 June 4, using the high-resolution data obtained by the New Vacuum Solar Telescope, the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph. At the beginning, the right footpoint of the filament is rooted in the AR positive polarity, and its right leg has a spread-out structure, which is confirmed by the extrapolated 3D magnetic structure. Many small positive and negative magnetic polarities connected by EUV-emitting loops gradually appear between two extensions of the right footpoint polarity as the extensions separate. The right leg of the filament is then observed to split into two parts, which continue to separate, while the left part of the filament still maintains a whole structure. As the newly emerged magnetic loops rise between the two parts of the right leg, magnetic reconnection occurs between the newly emerged magnetic loops and the magnetic fields supporting the southeastern splitting part. The longer magnetic loops resulting from this reconnection merge with the magnetic fields of the other part of the split filament leg, thus reforming an entire filament with a displaced right footpoint. We conclude that magnetic emergence is responsible for the splitting of the filament leg, while magnetic reconnection leads to the reconstruction of the filament. [ABSTRACT FROM AUTHOR]

We use Parker Solar Probe (PSP) observations to report the first direct measurements of the particle and field environments while crossing the leg of a coronal mass ejection (CME) very close to the Sun (∼14 Rs). An analysis that combines imaging from 1 au and PSP with a CME model, predicts an encounter time and duration that correspond to an unusual, complete dropout in low-energy solar energetic ions from H–Fe, observed by the Integrated Science Investigation of the Sun (IS⊙IS). The surrounding regions are populated with low-intensity protons and heavy ions from 10s to 100 keV, typical of some quiet times close in to the Sun. In contrast, the magnetic field and solar wind plasma show no similarly abrupt changes at the boundaries of the dropout. Together, the IS⊙IS energetic particle observations, combined with remote sensing of the CME and a dearth of other "typical" CME signatures, indicate that this CME leg is significantly different from the magnetic and plasma structure normally assumed for CMEs near the Sun and observed in interplanetary CMEs farther out in the solar wind. The dropout in low-energy energetic ions may be due to the cooling of suprathermal ions at the base of the CME leg flux tube, owing to the rapid outward expansion during the release of the CME. [ABSTRACT FROM AUTHOR]

We explore the processes of the repetitive buildup and the explosive release of magnetic energy, together with the formation of magnetic flux ropes, which eventually resulted in three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 between 2014 March 28 and 29. EUV observations and magnetogram measurements, together with coronal magnetic field modeling, suggest that the flares were triggered by the eruption of flux ropes that were embedded in a densely packed system of loops within a small part of the active region. In X-rays, the first and second events show similar evolutions, with single compact sources, while the third event exhibits multiple emission centroids, with a set of strong nonthermal conjugate sources at 50–100 keV during the hard X-ray peak. Over an interval of ≈ 44 hr, the photospheric magnetic field encompassing the three flares undergoes important phases of emergence and cancellation, together with significant changes near the polarity inversion lines within the flaring region. Our observations point toward the tether-cutting mechanism being the plausible triggering process of the eruptions. Between the second and third events, we observe a prominent phase of flux emergence that temporally correlates with the buildup phase of free magnetic energy in the active region corona. In conclusion, our analysis reveals efficient coupling between the rapidly evolving photospheric and coronal magnetic fields in the active region, leading to a continued phase of the buildup of free energy, which results in the homologous flares of successively increasing intensities. [ABSTRACT FROM AUTHOR]

We present in this Letter the first global comparison between traditional line-tied steady-state magnetohydrodynamic models and a new, fully time-dependent thermodynamic magnetohydrodynamic simulation of the global corona. To approximate surface magnetic field distributions and magnitudes around solar minimum, we use the Lockheed Evolving Surface-Flux Assimilation Model to obtain input maps that incorporate flux emergence and surface flows over a full solar rotation, including differential rotation and meridional flows. Each time step evolves the previous state of the plasma with a new magnetic field input boundary condition, mimicking photospheric driving on the Sun. We find that this method produces a qualitatively different corona compared to steady-state models. The magnetic energy levels are higher in the time-dependent model, and coronal holes evolve more along the following edge than they do in steady-state models. Coronal changes, as illustrated with forward-modeled emission maps, evolve on longer timescales with time-dependent driving. We discuss implications for active and quiet Sun scenarios, solar wind formation, and widely used steady-state assumptions like potential field source surface calculations.

One key aspect of understanding the solar dynamo mechanism and the evolution of solar magnetism is to properly describe the emergence of solar active regions. In this Letter, we describe the Lagrangian photospheric flows dynamics during a simulated flux emergence that produces an active region formed by pores. We analyze the lower photospheric flow organization prior, during and following the rise of an active region, uncovering the repelling and attracting photospheric structures that act as sources and sinks for magnetic element transport. Our results show that around 10 hr before the simulated emergence, considerable global changes are taking place on mesogranular scales indicated by an increase of the number of regions acting as a source to the multiple and scattered emergences of small-scale magnetic flux. At the location of active region’s appearance, the converging flows become weaker and there is an arising of a diverging region 8 hr before the emergence time. Our study also indicates that the strong concentration of magnetic field affects the flow dynamics beyond the area of the actual simulated pores, leading to complex and strongly diverging flows in the neighboring regions. Our findings suggest that the Lagrangian analysis is a powerful tool to describe the changes in the photospheric flows due to magnetic flux emergence.

Flux emergence is responsible for various solar eruptions. Combining observation and simulations, we investigate the influence of flux emergence at one footpoint of an arcade on coronal rain as well as induced eruptions. The emergence changes the pressure in the loops, and the internal coronal rain all moves to the other side. The emerging flux reconnects with the overlying magnetic field, forming a current sheet and magnetic islands. The plasma is ejected outwards and heated, forming a cool jet ∼6000 K and a hot X-ray jet ∼4 million Kelvin (MK) simultaneously. The jet dynamical properties agree very well between observation and simulation. In the simulation, the jet also displays transverse oscillations with a period of 8 minutes, in a so-called whiplike motion. The movement of the jet and dense plasmoids changes the configuration of the local magnetic field, facilitating the occurrence of the Kelvin–Helmholtz instability, and vortex-like structures form at the boundary of the jet. Our simulation clearly demonstrates the effect of emergence on coronal rain, the dynamical details of reconnecting plasmoid chains, the formation of multithermal jets, and the cycling of cool mass between the chromosphere and the corona.

Bipolar magnetic regions (BMRs) provide crucial information about solar magnetism. They exhibit varying morphology and magnetic properties throughout their lifetime, and studying these properties can provide valuable insights into the workings of the solar dynamo. The majority of previous studies have counted every detected BMR as a new one and have not been able to study the full life history of each BMR. To address this issue, we have developed Automatic Tracking Algorithm for BMRs (AutoTAB) that tracks the BMRs for their entire lifetime or throughout their disk passage. AutoTAB uses the binary maps of detected BMRs and their overlapping criterion to automatically track the regions. In this first article of this project, we provide a detailed description of the working of the algorithm and evaluate its strengths and weaknesses by comparing it with existing algorithms. AutoTAB excels in tracking even for the small BMRs (with a flux of ∼10 ^20 Mx), and it has successfully tracked 9152 BMRs over the last two solar cycles (1996–2020), providing a comprehensive data set that depicts the evolution of various properties for each BMR. The tracked BMRs exhibit the well-known butterfly diagram and 11 yr solar cycle variation, except for small BMRs, which appear at all phases of the solar cycle and show a weak latitudinal dependence. Finally, we discuss the possibility of adapting our algorithm to other data sets and expanding the technique to track other solar features in the future.

Magnetic flux ropes are a key component of coronal mass ejections, forming the core of these eruptive phenomena. However, determining whether a flux rope is present prior to eruption onset and, if so, the rope’s handedness and the number of turns that any helical field lines make is difficult without magnetic field modeling or in situ detection of the flux rope. We present two distinct observations of plasma flows along a filament channel on 2022 September 4 and 5 made using the Solar Orbiter spacecraft. Each plasma flow exhibited helical motions in a right-handed sense as the plasma moved from the source active region across the solar disk to the quiet Sun, suggesting that the magnetic configuration of the filament channel contains a flux rope with positive chirality and at least one turn. The length and velocity of the plasma flow increased from the first to the second observation, suggesting evolution of the flux rope, with the flux rope subsequently erupting within ∼5 hr of the second plasma flow. The erupting flux rope then passed over the Parker Solar Probe spacecraft during its encounter (13), enabling in situ diagnostics of the structure. Although complex and consistent with the flux rope erupting from underneath the heliospheric current sheet, the in situ measurements support the inference of a right-handed flux rope from remote-sensing observations. These observations provide a unique insight into the eruption and evolution of a magnetic flux rope near the Sun.

We have performed 3D numerical simulations to investigate the effect of partial ionization on the process of magnetic flux emergence. In our study, we have modified the single-fluid MHD equations to include the presence of neutrals and have performed two basic experiments: one that assumes a fully ionized plasma (FI case) and one that assumes a partially ionized plasma (PI case). We find that the PI case brings less dense plasma to and above the solar surface. Furthermore, we find that partial ionization alters the emerging magnetic field structure, leading to a different shape of the polarities in the emerged bipolar regions compared to the FI case. The amount of emerging flux into the solar atmosphere is larger in the PI case, which has the same initial plasma beta as the FI case, but a larger initial magnetic field strength. The expansion of the field above the photosphere occurs relatively earlier in the PI case, and we confirm that the inclusion of partial ionization reduces cooling due to adiabatic expansion. However, it does not appear to work as a heating mechanism for the atmospheric plasma. The performance of these experiments in three dimensions shows that PI does not prevent the formation of unstable magnetic structures, which erupt into the outer solar atmosphere.

We present a method of conducting data-driven simulations of solar active regions and flux emergence with the MURaM radiative magnetohydrodynamics (MHD) code. The horizontal electric field that is derived from the full velocity and magnetic vectors is implemented at the photospheric (bottom) boundary to drive the induction equation. The energy equation accounts for thermal conduction along magnetic fields, optically thin radiative loss, and heating of coronal plasma by viscous and resistive dissipation, which allows for a realistic presentation of the thermodynamic properties of coronal plasma that are key to predicting the observational features of solar active regions and eruptions. To validate this method, the photospheric data from a comprehensive radiative MHD simulation of solar eruption (the ground truth) are used to drive a series of numerical experiments. The data-driven simulation reproduces the accumulation of free magnetic energy over the course of flux emergence in the ground truth with an error of 3%. The onset time is approximately 8 minutes delayed compared to the ground truth. However, a precursor-like signature can be identified at the correct onset time. The data-driven simulation captures key eruption-related emission features and plasma dynamics of the ground truth flare over a wide temperature span, from ${\mathrm{log}}_{10}T=4.5$ to ${\mathrm{log}}_{10}T\gt 8$ . The evolution of the flare and coronal mass ejection as seen in synthetic extreme ultraviolet images is also reproduced with high fidelity. This method helps to understand the evolution of magnetic field in a more realistic coronal environment and to link the magnetic structures to observable diagnostics.

We investigate deviations in the mean phase travel time of acoustic waves preceding the emergence of 46 large active regions observed by the Helioseismic and Magnetic Imager. In our investigation, we consider two different procedures for obtaining the mean phase travel time, by minimizing the difference between cross-correlations and a reference, as well as the Gabor wavelet fitting procedure. We cross-correlate the time series of mean phase travel time deviations with the surface magnetic field and determine the peak correlation time lag. We also compute the perturbation index—the area integrated mean phase travel time deviations exceeding quiet Sun thresholds—and compare the time of peak perturbation index with the correlation time lag. We find that the lag times derived from the difference minimization procedure precede the flux emergence for 36 of the 46 active regions, and that this lag time has a noticeable correlation with the maximum flux rate. However, only 28 of the active regions have peak perturbation index times in the range of 24–48 hr prior to the flux emergence. Additionally, we examine the relationship between the properties of the emerged active regions and the strength of helioseismic signals prior to their emergence.

We explore the processes of the repetitive buildup and the explosive release of magnetic energy, together with the formation of magnetic flux ropes, which eventually resulted in three homologous eruptive flares of successively increasing intensities (i.e., M2.0, M2.6, and X1.0). The flares originated from NOAA active region 12017 between 2014 March 28 and 29. EUV observations and magnetogram measurements, together with coronal magnetic field modeling, suggest that the flares were triggered by the eruption of flux ropes that were embedded in a densely packed system of loops within a small part of the active region. In X-rays, the first and second events show similar evolutions, with single compact sources, while the third event exhibits multiple emission centroids, with a set of strong nonthermal conjugate sources at 50–100 keV during the hard X-ray peak. Over an interval of ≈ 44 hr, the photospheric magnetic field encompassing the three flares undergoes important phases of emergence and cancellation, together with significant changes near the polarity inversion lines within the flaring region. Our observations point toward the tether-cutting mechanism being the plausible triggering process of the eruptions. Between the second and third events, we observe a prominent phase of flux emergence that temporally correlates with the buildup phase of free magnetic energy in the active region corona. In conclusion, our analysis reveals efficient coupling between the rapidly evolving photospheric and coronal magnetic fields in the active region, leading to a continued phase of the buildup of free energy, which results in the homologous flares of successively increasing intensities.

The Mg ii h and k lines are among the best diagnostic tools of the upper solar chromosphere. This region of the atmosphere is of particular interest, as it is the lowest region of the Sun’s atmosphere where the magnetic field is dominant in the energetics and dynamics, defining its structure. While highly successful in the photosphere and lower to mid-chromosphere, numerical models have produced synthetic Mg ii lines that do not match the observations well. We present a number of large-scale models with magnetic field topologies representative of the quiet Sun, ephemeral flux regions and plage, and also models where the numerical resolution is high and where we go beyond the MHD paradigm. The results of this study show models with a much improved correspondence with IRIS observations in terms of both intensities and widths, especially underscoring the importance of chromospheric mass loading and of capturing the magnetic field topology and evolution in simulations. This comes in addition to the importance of capturing the generation of small-scale velocity fields and including nonequilibrium ionization and ion−neutral interaction effects. However, it should be noted that difficulties in achieving a good correspondence remain, especially when considering the width of Mg ii h and k lines in plage. Understanding and modeling all these effects and their relative importance is necessary in order to reproduce observed spectral features and in isolating the missing pieces necessary to fully comprehend Mg ii formation.

Coronal bright points (CBPs) are sets of small-scale coronal loops, connecting opposite magnetic polarities, primarily characterized by their enhanced extreme-ultraviolet (EUV) and X-ray emission. Being ubiquitous, they are thought to play an important role in heating the solar corona. We aim at characterizing the barely explored chromosphere underneath CBPs, focusing on the related spicular activity and on the effects of small-scale magnetic flux emergence on CBPs. We used high-resolution observations of a CBP in H β and Fe i 617.3 nm from the Swedish 1 m Solar Telescope in coordination with the Solar Dynamics Observatory. This work presents the first high-resolution observation of spicules imaged in H β . The spicules were automatically detected using advanced image processing techniques, which were applied to the Dopplergrams derived from H β . Here we report their abundant occurrence close to the CBP “footpoints” and find that the orientation of such spicules is aligned along the EUV loops, indicating that they constitute a fundamental part of the whole CBP magnetic structure. Spatiotemporal analysis across multiple channels indicates that there are coronal propagating disturbances associated with the studied spicules, producing transient EUV intensity variations of the individual CBP loops. Two small-scale flux emergence episodes appearing below the CBP were analyzed, one of them leading to quiet-Sun Ellerman bombs and enhancing the nearby spicular activity. This paper presents unique evidence of the tight coupling between the lower and upper atmosphere of a CBP, thus helping to unravel the dynamic phenomena underneath CBPs and their impact on the latter.

We present observations and interpretation of a nonerupting filament in NOAA active region (AR) 12827 that undergoes splitting and restructuring on 2021 June 4, using the high-resolution data obtained by the New Vacuum Solar Telescope, the Solar Dynamics Observatory, and the Interface Region Imaging Spectrograph. At the beginning, the right footpoint of the filament is rooted in the AR positive polarity, and its right leg has a spread-out structure, which is confirmed by the extrapolated 3D magnetic structure. Many small positive and negative magnetic polarities connected by EUV-emitting loops gradually appear between two extensions of the right footpoint polarity as the extensions separate. The right leg of the filament is then observed to split into two parts, which continue to separate, while the left part of the filament still maintains a whole structure. As the newly emerged magnetic loops rise between the two parts of the right leg, magnetic reconnection occurs between the newly emerged magnetic loops and the magnetic fields supporting the southeastern splitting part. The longer magnetic loops resulting from this reconnection merge with the magnetic fields of the other part of the split filament leg, thus reforming an entire filament with a displaced right footpoint. We conclude that magnetic emergence is responsible for the splitting of the filament leg, while magnetic reconnection leads to the reconstruction of the filament.

Solar pores are closely related to the concentration, dissipation, and transportation of solar magnetic flux. Their observable characteristics can provide constraints on models and simulations of magnetic flux emergence and formation. The specific property investigated in this study is their horizontal movement. The aim is to investigate whether the movement is correlated with any observable quantities. Our statistical analysis of 61 compact pores identified from the Spaceweather HMI Active Region Patches (SHARP) from 2011 to 2018 indicates that the direction of movement is often either parallel or antiparallel to the direction of maximum magnetic pressure difference ( dP _mag ) at the opposite sides of the edges of the pores. The correlation coefficients for both the parallel and antiparallel cases are higher than 0.74. Despite the high correlation, our analysis using the transfer entropy indicates no significant causal relationship between the direction of motion and the direction of maximum dP _mag .

This article presents results that challenge the paradigms that (1) the convection zone is the source of the radial magnetic field in the photosphere and (2) that coronal currents are neutralized from the perspective of the photosphere. We demonstrate, using a new analysis tool applied to simulations and observations, that bare or partially dressed current channels are supported by the solar corona and that fingerprints of these coronal current systems can be detected in the photosphere. These coronal current channels can be a significant source of the radial component of the magnetic field in the photosphere. The roots of these coronal current channels in the photosphere are the source of the magnetic field component parallel to the polarity inversion line in active region NOAA 12673. These analyses and observations transform our theoretical understanding of coronal evolution and argue for a reexamination of the present paradigm in which the convection zone is the sole source of the photospheric magnetic field.