Jing Ye

Solar flares are the largest energy releasing events in the solar system, where the open magnetic field lines reconnect and form the closed flare loops. During this process, rapid magnetic reconnection, the associated shock waves, and chromospheric evaporation are expected but not yet well understood. These processes are crucial for understanding similar features in stellar flares and other astrophysical jets. Here, we report the characteristics of propagating slow-mode shocks in the flare loop system, by combining a 3D high-resolution magnetohydrodynamics modeling and spectral analysis of Extreme Ultra-Violet observations. It is found that normal slow shocks are recurrently formed after the collision between the post-reconnection downflows and evaporation flows in the flare loops, which subsequently propagate toward the chromosphere at speeds comparable to the evaporation flows. In particular, the Doppler analysis of the Fe XXI 1354 Å line normally shows a sharp change in blueshifted velocity and an asymmetrical line broadening once the line-of-sight passes through the shock front. This study highlights that propagation of slow shocks can facilitate energy release in flares and affect energy transport, suggesting an advancement in the standard flare model framework.

Non-equilibrium ionization (NEI) is a critical physical process in astrophysical environments where the plasma's thermodynamic timescales are shorter than the ionization or recombination timescales, such as in the solar wind and solar eruptions. In such rapidly evolving plasmas, the charge states of ions are governed by time-dependent ionization equations. In this work, we report a package designed to perform fast NEI calculations using the eigenvalue method. A key feature of this package is that it can be applied in various plasma environments with arbitrary non-Maxwellian electron distributions. Furthermore, it supports both post-process analysis by tracking the movement of plasma deduced from MHD simulation and in-line calculation within MHD modeling. Finally, we show one application of this package in investigating solar wind evolution with various Kappa electron distributions. This code is freely available for download from the Web.

Solar flares are the largest energy releasing events in the solar system, where the open magnetic field lines have reconnected and form the closed flare loops. During this process, rapid magnetic reconnection, the associated shock waves, and chromospheric evaporation are expected but not yet well understood. These processes are crucial for understanding similar features in stellar flares and other astrophysical jets. Here, we present a series of high-resolusion three-dimensional magnetohydrodynamics simulations for a typical solar eruption, due to loss of equilibrium for a pre-existing flux rope in the corona. Firstly, a complex evolution of plasmoids in the reconnection current sheet is witnessed in 3D, such as the splitting, merging and kinking processes. And the anisotropy of the turbulence shows a significant variation in the spectra with height. Secondly, the 3D Quasi-periodic fast propagating waves generated during the eruption are demonstrated to be composed of three distinct components: fast-mode shock, rarefaction wave and the transition region between them. The anisotropy of the 3D CME shock waves is responsible for the dome-like wave front observed in the extreme ultraviolet waves. Lastly, we found that normal slow shocks are recurrently formed after the collision between the post-reconnection downflows and evaporation flows in the flare loops, which subsequently propagate toward the chromosphere at speeds comparable to the evaporation flows. Our simulation and spectrum observation provide the reliable evidence to support the presence of the normal slow shocks on the leg of the flare loops, suggesting a significant advancement in the standard flare model framework.

Newly emerging flux (NEF) has been widely studied as a trigger of solar filament eruptions, but its influence on the subsequent dynamics remains poorly explored. Because NEF typically emerges adjacent to filaments, it imposes magnetic asymmetry that can drive nonradial eruptions and complicate space-weather forecasting. We bridge analytic catastrophe theory with 2D resistive MHD simulations: analytic solutions provide magnetic configurations containing a flux rope at the loss-of-equilibrium point, which are then used as initial conditions for simulations to examine the following dynamics. We find that NEF governs the kinematics of filament eruptions in two ways. First, by reshaping coronal stability, NEF can create or eliminate a higher equilibrium in the corona, thereby producing failed eruptions or coronal mass ejections (CMEs). In the transitional situation where a metastable equilibrium appears, the rising filament decelerates and stalls before reaccelerating into a CME, consistent with observed two-step eruptions. Second, by breaking symmetry, NEF deflects eruptions away from the radial direction: depending on its polarity, it acts as a repulsor or an attractor on eruptive filaments, and the deflection magnitude increases with the degree of asymmetry. Our theory yields two characteristic angles that predict the deflection directions of CMEs and failed eruptions, and simulations closely align with these predictors. These results highlight the NEF not only as a trigger but also as a key factor that governs both the acceleration and deflection of eruptions during their propagation in the low corona.

Through three-dimensional MHD simulations, we have uncovered a kind of fast coronal wave originating from both ends of a current sheet (CS) during a solar eruption. These waves are observed to appear near the top and bottom ends of the reconnection-related CS. The simulations demonstrate the presence of termination shock regions above the two ends of the CS. As the reconnection outflows escape from the vertical CS and encounter these termination shocks, they undergo partial reflection, redirecting toward the CS terminal fork walls. The identified waves propagate rapidly at a speed of approximately 1400 km s ⁻¹ with a period of just 2 s. Concurrently, the time evolution of intensity within a small region of the CS terminal fork structures exhibits a similar oscillation period of 2 s. All this evidence supports the notion that these quasiperiodic fast-propagating (QFP) waves were excited by tuning-fork effects within the CS system. Essentially, the rapid reconnection outflows are reflected by the terminal shocks, striking the fork walls at the CS ends. Moreover, parts of the oscillations along the tuning-fork handle are transformed into thermal energy, accumulating in the CS center and elevating the temperature. This is the first time to report such QFP waves resulting from tuning-fork effects within the CS during a solar eruption. These waves are anticipated to manifest closely following the propagation of CMEs and adjacent to the related postflare loops in observations, with partial confirmation in current observations.

Newly emerging flux (NEF) has been widely studied as a trigger of solar filament eruptions, but its influence on the subsequent dynamics remains poorly explored. Because NEF typically emerges adjacent to filaments, it imposes magnetic asymmetry that can drive non-radial eruptions and complicate space-weather forecasting. We bridge analytic catastrophe theory with 2D resistive MHD simulations: analytic solutions provide magnetic configurations containing a flux rope at the loss-of-equilibrium point, which are then used as initial conditions for simulations to examine the following dynamics. We find that NEF governs the kinematics of filament eruptions in two ways. First, by reshaping coronal stability, NEF can create or eliminate a higher equilibrium in corona, thereby producing failed eruptions or CMEs. In the transitional situation where a metastable equilibrium appears, the rising filament decelerates and stalls before re-accelerating into a CME, consistent with observed two-step eruptions. Second, by breaking symmetry, NEF deflects eruptions away from the radial direction: depending on its polarity, it acts as a repulsor or an attractor on eruptive filaments, and the deflection magnitude increases with the degree of asymmetry. Our theory yields two characteristic angles that predict the deflection directions of CMEs and failed eruptions, and simulations closely aligns with these predictors. These results highlight the NEF not only as a trigger but also as a key factor that governs both the acceleration and deflection of eruptions during their propagation in the low corona.

We performed numerical simulations of magnetic reconnection with different strengths of magnetic fields from the solar photosphere to the upper chromosphere. The main emphasis is to identify dominant mechanisms for heating plasmas in the reconnection region under different plasma-β conditions in the partially ionized low solar atmosphere. The numerical results show that more plasmoids are generated in a lower β reconnection event. The frequent coalescence of these plasmoids leads to a significant enhancement of turbulence and compression heating, which becomes the dominant mechanism for heating plasma in a lower plasma-β reconnection process. The average power density of the compression heating (Q _comp) decreases with increasing initial plasma-β as a power function: Q comp ∼ β 0 − a , where the value a is 1.9 in the photosphere and decreases to about 1.29 in the upper chromosphere. In the photosphere and lower chromosphere, the Joule heating contributed by electron-neutral collisions Q _en = η _en J ² eventually dominates over the compression heating when the initial plasma-β is larger than the critical value β _0−critical = 8. In the upper chromosphere, the ambipolar diffusion heating and the viscous heating will become equally important as the compression heating when the initial plasma-β is larger than the critical value β _0−critical = 0.5. These results indicate that the compression heating caused by turbulent reconnection mediated with plasmoids is likely the major heating mechanism for the small-scale reconnection events with stronger magnetic fields, such as active region Ellerman bombs (EBs) and UV bursts. However, the heating caused by the partial ionization effects can not be ignored for those reconnection events with weaker magnetic fields, such as quiet Sun EBs and cold surges.

The propagation of disturbances in the solar atmosphere is inherently three dimensional (3D), yet comprehensive studies on the spatial structure and dynamics of 3D wavefronts are scarce. Here we conduct high resolution 3D numerical simulations to investigate filament eruptions, focusing particularly on the 3D structure and genesis of EUV waves. Our results demonstrate that the EUV wavefront forms a dome like configuration subdivided into three distinct zones. The foremost zone, preceding the flux rope, consists of fast-mode shock waves that heat the adjacent plasma. Adjacent to either side of the flux rope, the second zone contains expansion waves that cool the nearby plasma. The third zone, at the juncture of the first two, exhibits minimal disturbances. This anisotropic structure of the wavefront stems from the configuration and dynamics of the flux rope, which acts as a 3D piston during eruptions :compressing the plasma ahead to generate fast mode shocks and evacuating the plasma behind to induce expansion waves. This dynamic results in the observed anisotropic wavefront.Additionally, with synthetic EUV images from simulation data, the EUV waves are observable in Atmospheric Imaging Assembly 193 and 211 angstrom, which are identified as the fast mode shocks. The detection of EUV waves varies with the observational perspective: the face on view reveals EUV waves from the lower to the higher corona, whereas an edge on view uncovers these waves only in the higher corona.

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.