Flux Tubes Research Articles

Data-driven MHD Simulation of the Formation of a Magnetic Flux Rope and an Inclined Solar Eruption

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.

Galactic outflows in different geometries

In the gravitational potential well of a galaxy, the behavior of outflows has been studied in different geometries i.e. constant flux tube, divergent and extreme divergent environments. First of all, we describe the hydrodynamic model by which we approach the outflows system. This model treats all the waves as fluids and applies fluid mechanics to them(cosmic rays, thermal plasma & Alfvén wave). Whereas outflows mean the gas regime above and below the center of the galactic disk, and we have taken it as a system where interaction between cosmic rays and plasma occurs. After discussing the hydrodynamic three-fluid model, we define three geometrical structures which can be acquired by outflows and relate these structures with thermal plasma, cosmic and Alfvén waves pressures, thus seeking for its behavior. The solution of the system is categorically divided into three branches, supersonic, subsonic and unphysical solutions.The most interesting of all is the transonic solution, a solution that evolves from subsonic to supersonic. First of all, we discuss only thermal plasma outflows and explain their evolution in three cases of outflows environments, followed by the addition of cosmic waves and Alfvén waves. After discussing three fluid outflows in different structures, we compared the results of thermal outflows with three fluid outflows and see how the addition of waves in the system affects the dynamics of the system. At last, the findings of this paper are discussed.

Slowly positively drifting bursts generated by large-scale magnetic reconnection

Context. The slowly positively drifting bursts (SPDBs) are rarely observed in radio emission of solar flares. Aims. To understand how the SPDBs are generated, we studied the radio observations at 600–5000 MHz together with the imaging observations made in ultraviolet (UV) and extreme ultraviolet (EUV) during the SPDB-rich C8.7 flare of 2014 May 10 (SOL2014-05-10T0702). Methods. Because the SPDBs propagate towards locations of higher plasma density, we studied their associations with individual flare kernels, located either within the flare core itself, or distributed at longer distances, but connected to the flaring region by large-scale hot loops. For each kernel we constructed light curves using 1600 Å and 304 Å observations and compared these light curves with the temporal evolution of radio flux at 1190 MHz, representing all observed groups of SPDBs. We also analysed the UV/EUV observations to understand the evolution of magnetic connectivity during the flare. Results. The flare starts with a growing hot sigmoid observed in 131 Å. As the sigmoid evolves, it extends to and interacts with a half dome present within the active region. The evolving sigmoid reconnects at the respective hyperbolic flux tube, producing large-scale magnetic connections and an EUV swirl. Three groups of SPDBs are observed during this large-scale magnetic reconnection, along with a group of narrow-band type III bursts. The light curves of a kernel corresponding to the footpoint of spine line analogue show good agreement with the radio flux at 1190 MHz, indicating that the SPDBs are produced by the large-scale magnetic reconnection at the half dome. In addition, one of the kernels appeared in the neighbouring active region and also showed a similar evolution to the radio flux, implying that beams of accelerated particles can synchronize radio and UV/EUV light curves across relatively large distances.

Verification of the kinetic electron role in the microinstabilities in a negative triangularity model equilibrium

Effect of kinetic electrons on negative triangularity plasmas has been investigated and compared against the corresponding positive triangularity plasmas, using the global gyrokinetic code X-point Gyrokinetic Code with scale-separated delta-f option without Coulomb collisions. Our model magnetic equilibria have strong positive and negative triangularities and weak magnetic shear. However, unusually large ρi/a and low density plasmas are chosen to maximize the nonlocal effect to investigate the finite ρi effect and to be clearly away from kinetic ballooning modes. Similar conclusions to previous flux tube and global simulations have been obtained in this highly nonlocal model plasma: it is essential to include kinetic electrons in the micro-instability study of negative triangularity plasmas. Most physics findings agree with existing reports, with some disagreement. We offer a new “effective trapping fraction” concept that can add to the explanation of the growth rate difference between NT and PT plasmas, pointing to the significant variation in trapped particle fractions that have turning points in the mode growth regions.

Why Could a Newborn Active Region Produce Coronal Mass Ejections?

Solar active regions (ARs) are the main sources of flares and coronal mass ejections (CMEs). NOAA AR 12089, which emerged on 2014 June 10, produced two C-class flares accompanied by CMEs within 5 hr after its emergence. When producing the two eruptive flares, the total unsigned magnetic flux (ΦAR) and magnetic free energy (E f ) of the AR are much smaller than the common CME-producing ARs. Why can this extremely small AR produce eruptive flares so early? We compare the AR magnetic environment for the eruptive flares to that for the largest confined flare from the AR. In addition to the ΦAR and E f , we calculate the ratio between the mean characteristic twist parameter (α FPIL) within the flaring polarity inversion line (FPIL) region and ΦAR, a parameter considering both background magnetic field constraint and nonpotentiality of the core region, for the three flares. We find higher α FPIL/ΦAR values during the eruptive flares than during the confined flare. Furthermore, we compute the decay index along the polarity inversion line, revealing values of 1.69, 3.45, and 0.98 before the two eruptive and the confined flares, respectively. Finally, nonlinear force-free field extrapolation indicates that a flux rope was repeatedly formed along the FPIL before eruptive flares, which ejected out and produced CMEs. No flux rope was found before the confined flare. Our research suggests that even a newly emerged, extremely small AR can produce eruptive flares if it has sufficiently weak background field constraint and strong nonpotentiality in the core region.

The Green's functions of two-dimensional piezoelectric quasicrystal semi-infinite crack and finite crack

This paper investigates the interactions of a semi-infinite crack / finite crack with multiple loadings in a two-dimensional piezoelectric quasicrystal under different boundary conditions. Utilizing the Stroh formalism and conformal mapping, Green's functions of generalized displacements and stresses are obtained for two general cases: a semi-infinite crack and a finite crack subject to free-free or fixed-fixed boundary conditions. The stress and electric displacement intensity factors at the crack tip and the image forces on how dislocations are affected by the crack surfaces are given explicitly. The results are analyzed and compared with special cases documented in the scholarly literature. At the same time, the effects of the Burgers vector components on the generalized stresses and image forces numerically illustrate as well as the impacts of line forces on generalized stress intensity factors.

Understanding the Effects of Spacecraft Trajectories through Solar Coronal Mass Ejection Flux Ropes Using 3DCOREweb

This study investigates the impact of spacecraft positioning and trajectory on in situ signatures of coronal mass ejections (CMEs). Employing the 3DCORE model, a 3D flux rope model that can generate in situ profiles for any given point in space and time, we conduct forward modeling to analyze such signatures for various latitudinal and longitudinal positions, with respect to the flux rope apex, at 0.8 au. Using this approach, we explore the appearance of the resulting in situ profiles for different flux rope types, with different handedness and inclination angles, for both high- and low-twist CMEs. Our findings reveal that CMEs exhibit distinct differences in signatures between apex hits and flank encounters, with the latter displaying elongated profiles with reduced rotation. Notably, constant, nonrotating in situ signatures are only observed for flank encounters of low-twist CMEs, suggesting the existence of untwisted magnetic field lines within CME legs. Additionally, our study confirms the unambiguous appearance of different flux rope types in in situ signatures in all of the cases, barring some indistinguishable cases, contributing to the broader understanding and interpretation of observational data. Given the model assumptions, this may refute trajectory effects as the cause for mismatching flux rope types as identified in solar signatures. While acknowledging limitations inherent in our model, such as the assumption of constant twist and a nondeformable torus-like shape, we still draw relevant conclusions within the context of the global magnetic field structures of CMEs and the potential for distinguishing flux rope types based on in situ observations.

Chromoelectric flux tubes within non-Abelian Proca theory

Flux tube solutions within non-Abelian SU(3) Proca theory with external sources are obtained. It is shown that such tubes have a longitudinal chromoelectric field possessing two components (nonlinear and gradient), as well as a transverse chromomagnetic field whose force lines create concentric circles with the center on the axis of the tube. The scenario of a possible relationship between non-Abelian Proca theory and quantum chromodynamics is considered. In such scenario: (a) the components of color fields have different behavior: those which are almost classical, and those which are purely quantum; (b) the second components create a gluon condensate that is a source of the field for the almost classical components of the Proca field; (c) Proca masses may appear as a result of an approximate description of the gluon condensate; (d) the question of gauge invariance is considered. It is shown that the results obtained are in good agreement with the results of lattice calculations. We make an assumption that an approximate description of a flux tube in quantum chromodynamics can be carried out using classical Proca equations but with a mandatory account of a gluon condensate.

Application of remote sensing navigation system in total knee arthroplasty

To explore clinical accuracy of remote sensing navigation alignment (RSNA) system in total knee arthroplasty (TKA) and its influence on postoperative clinical efficacy. From May 2021 to May 2022, 60 knee osteoarthritis (KOA) patients with Kellgren-Lawrence (K-L) grade Ⅲ to Ⅳ treated by unilateral primary TKA were selected and divided into RSNA group and traditional operation group according to treatment methods, and 30 patients in each group. There were 6 males and 24 females in RSNA group, aged from 55 to 86 years old with an average of (68.06±8.23) years old;body mass index (BMI) ranged from 22.15 to 34.58 kg·m-2 with an average of (28.20±3.01) kg·m-2;the courses of disease ranged from 2 to 60 months with an average of (18.80±14.80) months;13 patients with grade Ⅲ and 17 patients with grade Ⅳ according to K-L grading. In traditional operation group, there were 8 males and 22 females, aged from 57 to 85 years old with an average of (67.26±6.32) years old;BMI ranged from 23.94 to 34.55 kg·m-2 with an average of (27.49±2.32) kg·m-2;the courses of disease ranged from 3 to 60 months with an average of (21.30±16.44) months;14 patients with grade Ⅲ and 16 patients with grade Ⅳ according to K-L grading. Western Ontario and McMaster Universities (WOMAC) osteoarthritis index and Knee Society score(KSS) were used to evaluate functional recovery of patients. Hip-knee-ankle angle (HKAA), distal femoral valgus angle (FVA) and distal fermoral flexion angle (DFFA) were measured before operation. HKAA and HKAA deviation angle were measured at 1 week after operation, and defective rate of lower limb force line, femur prosthesis valgus angle (FPVA) and femoral prosthesis flexion angle (FPFA), respectively, were calculated. There were no serious complications such as vascular and nerve injury during operation, and wound healed at stage Ⅰ. Both groups were followed up for 6 months. There were no significant difference in WOMAC index, KSS, HKAA, FVA and DFFA between two groups before operation (P>0.05). The force line defect rate, HKAA, HKAA deviation angle, FPVA deviation angle and FPFA of RSNA group were 6.7%, (178.74±1.56) °, (1.25±1.56) °, (1.84±0.16) ° and (4.85±2.46) °, respectively;while in traditional operation group were 20%, (176.73±3.46) °, (3.27±3.46) °, (2.44±0.26) °, (6.60±1.86) °;the difference between two groups were statistically significant (P<0.05). There were no significant difference in WOMAC index and KSS between two groups at 3 and 6 months after operation (P>0.05). RSNA system could reduce defective rate of lower limb force line, FPVA deviation angle and FPFA after TKA, which is more accurate and easy to operate than traditional intramedullary localization surgery while ensuring postoperative efficacy.

High tibial osteotomy on varus knee osteoarthritis with medial meniscus posterior root injury

To explore clinical effect of distal tibial tubercle-high tibial osteotomy (DTT-HTO) in treating knee osteoarthritis (KOA) with medial meniscus posterior root tear (MMPRT). A retrospective analysis was performed on 21 patients with varus KOA with MMPRT from May 2020 to December 2021, including 3 males and 18 females, aged from 49 to 75 years old with an average of (63.81±6.56) years old, the courses of disease ranged from 0.5 to 18.0 years with an average of(5.9±4.2) years, and 4 patients with grade Ⅱ, 14 patients with grade Ⅲ, and 3 patients with grade Ⅳ according to Kellgren-Lawrence;14 patients with type 1 and 7 patients with type 2 according to MMPRT damage classification. The distance of medial meniscusextrusion (MME) and weight-bearing line ratio (WBLR) of lower extremity were compared before and 12 months after operation. Visual analogue scale (VAS), Western Ontarioand and McMaster Universities (WOMAC) osteoarthritis index, and Lysholm knee score were used to evaluate knee pain and functional improvement before operation, 1, 6 and 12 months after operation, respectively. Twenty-one patients were followed up for 12 to 18 months with an average of (13.52±1.72) months. MME distance was improved from (4.99±1.05) mm before operation to (1.87±0.76) mm at 12 months after operation (P<0.05). WBLR was increased from (15.49±7.04)% before operation to (62.71±2.27)% at 12 months after operation (P<0.05). VAS was decreased from (7.00±1.14) before operation to (2.04±0.80), (0.90±0.62) and (0.61±0.50) at 1, 6 and 12 months after operation. WOMAC were decreased from preoperative (147.90±9.88) to postoperative (103.43±8.52), (74.00±9.54) and (47.62±9.53) at 1, 6 and 12 months, and the difference were statistically significant (P<0.05). Lysholm scores were increased from (46.04±7.34) before oepration to (63.19±8.93), (81.10±6.41) and (89.29±3.04) at 1, 6 and 12 months after operation(P<0.05). For the treatment of varus KOA with MMPRT, DTT-HTO could reduce medial meniscus protrusion distance, improve the ratio of lower limb force line, and effectively reduce knee pain and improve knee joint function.

A retrospective study on two different surgical robots to assist total knee arthroplasty

To compare early clinical and imaging results of domestic HURWA and imported Brainlab Knee3 surgical robot-assisted knee replacement. A retrospective analysis was performed on 93 patients with knee osteoarthritis (KOA) who underwent robot-assisted descending total knee arthroplasty(TKA) from January 2021 to July 2023, and they were divided into BRATKA group and HRATKA group according to use of robotic system. There were 40 patients in BRATKA group, including 16 males and 24 females, aged from 55 to 90 years old with an average of (64.3±7.0) years old;27 patients with grade Ⅲ and 13 patients with grade Ⅳ according to Kellgren-Lawrence(K-L);18 patients on the right side and 22 patients on the left side;the courses of disease ranged from 1 to 30 years with an average of (15.3±7.6) years;imported Brainlab Knee3 surgical robot assisted system was adopted. There were 53 patients in HRATKA group, including 18 males and 35 females, aged from 52 to 81 years old with an average of (64.4±8.5) years old;30 patients with grade Ⅲ and 23 patients with grade Ⅳ;21 patients on the right side and 32 patients on the left side;the courses of disease ranged from 1 to 32 years with an average of (16.4±7.9) years;HURWA surgical robot assisted system was adopted. Operation time, perioperative total blood loss, incision length and postoperative complications were compared between two groups. Deviation angle of hip-knee-ankle angle(HKAA) before operation and on the first day after operation was compared between two groups. Later tibal component (LTC), frontal femoral component (FFC), later femoral component (LFC) and frontal tibal component(FTC) at 1 day after on the first day after operation was compared between two groups. Knee Society score(KSS), visual analogue scale (VAS) and range of motion (ROM) of knee joint were compared between two groups before operation and on the 3rd and 90th day after operation. Both groups were followed up for 11 to 18 months with an average of (14.4±2.1) months, and the wounds of all patients healed well. Operation time and incision length of BRATKA group were (132.1±34.6) min and (12.9±1.9) cm, while (94.1±10.8) min and (14.8±2.1) cm in HRATKA group, respectively, and the differences between two groups were statistically significant(P<0.05). There were no significant difference in perioperative total blood loss and preoperative deviation angle of HKAA between two groups(P>0.05). Deviation angle of HKAA, FFC angle and LFC angle in BRATKA group were (1.90±0.91) °, (87.90±1.51) ° and(9.00±3.2) °, respectively;while (0.93±1.04) °, (89.03±0.96) ° and (7.63±0.59) ° in HRATKA group, respectively, and the differences between two groups were statistically significant (P<0.05). There were no significant differences in FTC and LTC between two groups(P>0.05). There were no significant differences in VAS of knee rest and exercise, KSS score and ROM of knee joint between two groups before operation and 3 days and 90 days after operation(P>0.05). There was no significant difference in complications between two groups (P>0.05). Postoperative imaging of two robot systems showed good lower limb force line. The domestic HRATKA group had better LFC, FFC angle and HKA deviation angle than the imported BRATKA group, but there were no significant difference in postoperative knee function and pain relief.

Metrics depending on one variable in D -dimensional Einstein-Maxwell theory

We present new families of solutions of D-dimensional Einstein-Maxwell theory depending on one variable for all space-time signatures. The solutions found can be thought of as generalized Melvin solutions including flux tubes, domain walls, and cosmological space-times. Explicit examples are given in four and five space-time dimensions. Published by the American Physical Society 2024

On the sausage magnetohydrodynamic waves in magnetic flux tubes: finite plasma beta and phase mixing

Abstract Over the past twenty years, there has been increasing evidence of the existence of sausage waves in the solar atmosphere. These observations make them useful tools in the context of atmospheric seismology. Here, we study sausage magnetohydrodynamic waves in a magnetic flux tube of non-zero plasma beta with a circular cross-section and a radially inhomogeneous plasma density. Solving numerically the equations of motion for an initial value problem, the spatio-temporal evolution of the velocity perturbations is obtained for different sets of parameters. We show that the ratio of the amplitudes of the longitudinal and radial perturbations is determined by the amount of plasma beta. Additionally, the longitudinal component of the velocity perturbation experiences phase-mixing within a layer surrounding the boundary of the flux tube with a rate depending on the amount of plasma beta. The results revealed that in the presence of a non-zero plasma beta, the flux tube exhibits oscillations in both the radial and longitudinal directions, characterized by a combination of two frequencies: one belonging to the slow continuum and the other to the Alfvén continuum. Also, the period of radial oscillation is obtained for different sets of parameters. The dependence of the period of the radial oscillation on the wavenumber confirms the results obtained in previous studies.

Pitch-Angle Diffusion of Radiation Belt Electrons and Precipitating Particle Fluxes: Dependence on VLF Wavefield Parameters

The dependence of the pitch-angle diffusion efficiency of energetic electrons in the Earth’s magnetosphere on the distribution of the whistler wave field along the geomagnetic flux tube is quantitatively studied for parameters corresponding to the location of the Sura and HAARP HF heating facilities. The expansion of the precipitation energy range with the increase of the region of geomagnetic latitudes occupied by the waves is shown. Using the calculated pitch-angle diffusion coefficient for a given spectrum of waves and their distribution along the flux tube, the ratio of the fluxes of precipitating and trapped particles at low altitude is determined. It is shown that at typical wave intensities corresponding to chorus VLF waves and plasmaspheric hiss, the fluxes of precipitating and trapped electrons can be comparable to each other. At the same time, for the wave amplitudes observed as a result of the action of heating facilities, the flux of precipitating electrons is negligible.

High-resolution observations of recurrent jets from an arch filament system

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. 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. 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. 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 Hbeta 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. The high-resolution SST observations (0 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.

Toroidal modified Miller-Turner CME model in EUHFORIA: Validation and comparison with flux rope and spheromak

Rising concerns about the impact of space-weather-related disruptions demand modelling and reliable forecasting of coronal mass ejection (CME) impacts. In this study, we demonstrate the application of the modified Miller-Turner (mMT) model implemented within EUropean Heliospheric FORecasting Information Asset (EUHFORIA) in forecasting the geo-effectiveness of observed coronal mass ejection (CME) events in the heliosphere. Our goal is to develop a model that not only has a global geometry, in order to improve overall forecasting, but is also fast enough for operational space-weather forecasting. We test the original full torus implementation and introduce a new three-fourths Torus version called the Horseshoe CME model. This new model has a more realistic CME geometry, and overcomes the inaccuracies of the full torus geometry. We constrain the torus geometrical and magnetic field parameters using observed signatures of the CMEs before, during, and after the eruption. We perform EUHFORIA simulations for two validation cases -- the isolated CME event of 12 July 2012 and the CME--CME interaction event of 8-10 September 2014. We performed an assessment of the model's capability to predict the most important $B_z$ component using the advanced dynamic time-warping (DTW) technique. The Horseshoe model predictions of CME arrival time and geo-effectiveness for both validation events compare well with the observations and are weighed against the results obtained with the spheromak and FRi3D models, which were already available in EUHFORIA. The runtime of the Horseshoe model simulations is close to that of the spheromak model, which is suitable for operational space weather forecasting. However, the capability of the magnetic field prediction at 1 AU of the Horseshoe model is close to that of the FRi3D model. In addition, we demonstrate that the Horseshoe CME model can be used for simulating successive CMEs in EUHFORIA, overcoming a limitation of the FRi3D model.

Non-equilibrium formation and relaxation of magnetic flux ropes at kinetic scales

Magnetic flux ropes are pivotal structures and building blocks in astrophysical and laboratory plasmas, and various equilibrium models have thus been studied in the past. However, flux ropes in general form at non-equilibrium, and their pathway from formation to relaxation is a crucial process that determines their eventual properties. Here we show that any localized current parallel to a background magnetic field will evolve into a flux rope via non-equilibrium processes. The detailed kinetic dynamics are exhaustively explained through single-particle and Vlasov analyses and verified through particle-in-cell simulations. This process is consistent with many proposed mechanisms of flux rope generation such as magnetic reconnection. A spacecraft observation of an example flux rope is also presented; by invoking the non-equilibrium process, its structure and properties can be explicated down to all six components of the temperature tensor.

Flux Rope Modeling of the 2022 September 5 Coronal Mass Ejection Observed by Parker Solar Probe and Solar Orbiter from 0.07 to 0.69 au

As both Parker Solar Probe (PSP) and Solar Orbiter (SolO) reach heliocentric distances closer to the Sun, they present an exciting opportunity to study the structure of coronal mass ejections (CMEs) in the inner heliosphere. We present an analysis of the global flux rope structure of the 2022 September 5 CME event that impacted PSP at a heliocentric distance of only 0.07 au and SolO at 0.69 au. We compare in situ measurements at PSP and SolO to determine global and local expansion measures, finding a good agreement between magnetic field relationships with heliocentric distance, but significant differences with respect to flux rope size. We use PSP/Wide-Field Imager for Solar Probe images as input to the ELlipse Evolution model based on Heliospheric Imager data (or ELEvoHI), providing a direct link between remote and in situ observations; we find a large discrepancy between the resulting modeled arrival times, suggesting that the underlying model assumptions may not be suitable when using data obtained close to the Sun, where the drag regime is markedly different in comparison to larger heliocentric distances. Finally, we fit the SolO's magnetometer and PSP's FIELDS data independently with the 3D Coronal ROpe Ejection (or 3DCORE) model, and find that many parameters are consistent between spacecraft. However, challenges are apparent when reconstructing a global 3D structure that aligns with arrival times at PSP and SolO, likely due to the large radial and longitudinal separations between spacecraft. From our model results, it is clear the solar wind background speed and drag regime strongly affect the modeled expansion and propagation of CMEs and need to be taken into consideration.

Coronal energy release by MHD avalanches

Context. Magnetohydrodynamic (MHD) instabilities, such as the kink instability, can trigger the chaotic fragmentation of a twisted magnetic flux tube into small-scale current sheets that dissipate as aperiodic impulsive heating events. In turn, the instability could propagate as an avalanche to nearby flux tubes and lead to a nanoflare storm. Our previous work was devoted to related 3D MHD numerical modeling, which included a stratified atmosphere from the solar chromosphere to the corona, tapering magnetic field, and solar gravity for curved loops with the thermal structure modelled by plasma thermal conduction, along with optically thin radiation and anomalous resistivity for 50 Mm flux tubes. Aims. Using 3D MHD modeling, this work addresses predictions for the extreme-ultraviolet (EUV) imaging spectroscopy of such structure and evolution of a loop, with an average temperature of 2–2.5 MK in the solar corona. We set a particular focus on the forthcoming MUSE mission, as derived from the 3D MHD modeling. Methods. From the output of the numerical simulations, we synthesized the intensities, Doppler shifts, and non-thermal line broadening in 3 EUV spectral lines in the MUSE passbands: Fe IX 171 Å, Fe XV 284 Å, and Fe XIX 108 Å, emitted by ∼1 MK, ∼2 MK, and ∼10 MK plasma, respectively. These data were detectable by MUSE, according to the MUSE expected pixel size, temporal resolution, and temperature response functions. We provide maps showing different view angles (front and top) and realistic spectra. Finally, we discuss the relevant evolutionary processes from the perspective of possible observations. Reults. We find that the MUSE observations might be able to detect the fine structure determined by tube fragmentation. In particular, the Fe IX line is mostly emitted at the loop footpoints, where we might be able to track the motions that drive the magnetic stressing and detect the upward motion of evaporating plasma from the chromosphere. In Fe XV, we might see the bulk of the loop with increasing intensity, with alternating filamentary Doppler and non-thermal components in the front view, along with more defined spots in the topward view. The Fe XIX line is very faint within the chosen simulation parameters; thus, any transient brightening around the loop apex may possibly be emphasized by the folding of sheet-like structures, mainly at the boundary of unstable tubes. Conclusions. In conclusion, we show that coronal loop observations with MUSE can pinpoint some crucial features of MHD-modeled ignition processes, such as the related dynamics, helping to identify the heating processes.

Propagating kink waves in an open coronal magnetic flux tube with gravitational stratification: Magnetohydrodynamic simulation and forward modelling

Context. In coronal open-field regions, such as coronal holes, there are many transverse waves propagating along magnetic flux tubes, which are generally interpreted as kink waves. Previous studies have highlighted their potential role in coronal heating, solar wind acceleration, and seismological diagnostics of various physical parameters. Aims. This study aims to investigate propagating kink waves, considering both vertical and horizontal density inhomogeneity, using 3D magnetohydrodynamic (MHD) simulations. Methods. We established a 3D MHD model of a gravitationally stratified open flux tube, incorporating a velocity driver at the lower boundary to excite propagating kink waves. Forward modelling was conducted to synthesise observational signatures of the Fe IX 17.1 nm line. Results. Resonant absorption and density stratification both affect the wave amplitude. When diagnosing the relative density profile with velocity amplitude, resonant damping needs to be properly considered to avoid a possible underestimation. In addition, unlike standing modes, propagating waves are believed to be Kelvin-Helmholtz stable. In the presence of vertical stratification, however, the phase mixing of transverse motions around the tube boundary can still induce small-scale structures, partially dissipating wave energy and leading to a temperature increase, especially at higher altitudes. Moreover, we conducted forward modeling to synthesise observational signatures, which revealed the promising potential of future coronal imaging spectrometers such as MUSE in resolving these wave-induced signatures. Also, the synthesised intensity signals exhibit apparent periodic variations, offering a potential method for indirectly observing propagating kink waves with current extreme ultraviolet imagers.