Solar Prominences Research Articles

Understanding the Lateral Drifting of an Erupting Filament with a Data-constrained Magnetohydrodynamic Simulation

Solar filaments often exhibit rotation and deflection during eruptions, which would significantly affect the geoeffectiveness of the corresponding coronal mass ejections (CMEs). Therefore, understanding the mechanisms that lead to such rotation and lateral displacement of filaments is a great concern to space weather forecasting. In this paper, we examine an intriguing filament eruption event observed by the Chinese Hα Solar Explorer and the Solar Dynamics Observatory. The filament, which eventually evolves into a CME, exhibits significant lateral drifting during its rising. Moreover, the orientation of the CME flux rope axis deviates from that of the pre-eruptive filament observed in the source region. To investigate the physical processes behind these observations, we perform a data-constrained magnetohydrodynamic simulation. Many prominent observational features in the eruption are reproduced by our numerical model, including the morphology of the eruptive filament, eruption path, and flare ribbons. The simulation results reveal that the magnetic reconnection between the flux rope leg and neighboring low-lying sheared arcades may be the primary mechanism responsible for the lateral drifting of the filament material. Such a reconnection geometry leads to flux rope footpoint migration and a reconfiguration of its morphology. As a consequence, the filament material hosted in the flux rope drifts laterally, and the CME flux rope deviates from the pre-eruptive filament. This finding underscores the importance of external magnetic reconnection in influencing the orientation of a flux rope axis during eruption.

Experimental Study of the Response of Sheared E × B Flow to Varying Ion–Neutral Collisions

Partially ionized plasma is a common occurrence in astrophysical and space environments. The emergence and development of plasma instabilities are significantly impacted by the inelastic collisions between the ions and neutrals in the partially ionized plasma, such as the charge exchange. In this study, the effect of the ion–neutral collisions on the sheared E × B flow was experimentally investigated. In the weak collision range, the shear-driven plasma instability, such as Kelvin–Helmholtz instability, was excited by the velocity-sheared flow. However, increasing ion–neutral collisions resulted in a decrease in the magnitude of the sheared E × B flow due to charge exchange–induced drag forces. Consequently, the Kelvin–Helmholtz instability is suppressed, and the Rayleigh–Taylor instability is triggered. The underlying mechanism was elucidated through experimental findings and numerical analysis. The result of this study proposes that a transition between the two modes occurred with increasing ion–neutral collision strength. It could be applied to the study of the solar chromosphere and prominence and planetary ionospheres, where plasma is partially ionized and the sheared E × B flow is often encountered.

Dynamics of Threads Wrapping a Filament's Leg Prior to the Eruption on 2021 October 28

Although the magnetic field structures of solar filaments have been studied for several decades, the detailed evolution of the structure around a filament prior to its eruption is rarely observed. On 2021 October 28 in AR 12887, a major solar flare (X1.0 class) occurred at 15:35 UT. Based on the Solar Dynamics Observatory high-spatial-resolution observations, we find this flare is associated with the eruption of two filaments, namely F1 and F2. The two filaments are initially independent. The western leg (WLEG) of F1 approaches the northern leg of F2, due to the continuous movement and rotation of the magnetic field in which the WLEG roots in. We find first that there are some threads wrapping the WLEG. Brightening and bidirectionally plasmoid flows that originate from a brightening are detected in these threads, then the threads disappear, and the two filaments connect. NLFFF extrapolation reveals that there is a toroidal magnetic structure enveloping the WLEG and corresponding spatially to the threads. It is expected that a filament is enveloped by toroidal magnetic fields. According to the observations and extrapolation, we suggest that these threads represent the toroidal magnetic fields wrapping the WLEG. This paper provides new details about the dynamics of the toroidal magnetic fields. Magnetic reconnection takes place in the toroidal fields and thus destroys the fields, then F1 and F2 connect, and subsequently, the two filaments erupt and the flare occurs.

“In the shape of a cooking pot over the fire”: Records of solar prominences in the 1180s

The second half of the 1180s witnessed an unusual number of solar eclipses visible within Europe in quick succession. These were recorded or referenced in a wide range of sources, from chronicles in Latin and Old Church Slavonic to the earliest epic poem from the medieval Rus’. A comparison between key elements of these accounts reveals several notable features. First, the identification of solar prominences. The account of the 1185 total eclipse from the Rus’ Laurentian Chronicle is well established in this context as the first probable textual witness to the phenomenon in Europe. It may not be the only one, however. A similar identification can be made within a Latin chronicle from England, by Gervase, monk of the community at Christ Church Cathedral Priory, for the total eclipse of 1187. Second, the contemporaneous nature of the descriptions is noteworthy, and more so in comparison with other contemporary accounts. A third area for focus concerns the nature of the observations and a case-study of Gervase of Canterbury who, if not an eye-witness to what he records, includes generally accurate accounts. These make his occasional inaccuracies all the more intriguing. Fourth, the wider comparison highlights the importance of taking account historical records across the European medieval heritage, Slavic and Orthodox alongside Latin and Catholic traditions.

Rotational Flows in Solar Coronal Flux Rope Cavities

We present a 2.5D magnetohydrodynamic simulation of a systematically rotating prominence inside its coronal cavity using the open-source MPI-AMRVAC code. Our simulation starts from a nonadiabatic, gravitationally stratified corona, permeated with a sheared arcade magnetic structure. The flux rope (FR) is formed through converging and shearing footpoints driving, simultaneously applying randomized heating at the bottom. The latter induces a left–right asymmetry of temperature and density distributions with respect to the polarity inversion line. This asymmetry drives flows along the loops before the FR formation, which gets converted to net rotational motions upon reconnection of the field lines. As the thermal instability within the FR develops, angular momentum conservation about its axis leads to a systematic rotation of both hot coronal and cold condensed plasma. The initial rotational velocity exceeds 60 km s−1. The synthesized images confirm the simultaneous rotations of the coronal plasma seen in 211 and 193 Å and condensations seen in 304 Å. Furthermore, the formation of the dark cavity is evident in 211 and 193 Å images. Our numerical experiment is inspired by observations of so-called giant solar prominence tornadoes and reveals that asymmetric FR formation can be crucial in triggering rotational motions. We reproduce observed spinning motions inside the coronal cavity, augmenting our understanding of the complex dynamics of rotating prominences.

Self-consistent equilibrium models of prominence thin threads heated by Alfvén waves propagating from the photosphere

The fine structure of solar prominences is composed of thin threads that outline the prominence magnetic field lines. Observations have shown that transverse waves of Alfvénic nature are ubiquitous in prominence threads. These waves are driven at the photosphere and propagate to prominences suspended in the corona. Heating due to Alfvén wave dissipation could be a relevant mechanism in the cool and partially ionised prominence plasma. In this work, we explore the construction of 1D equilibrium models of prominence thin threads that satisfy an energy balance condition between radiative losses, thermal conduction, and Alfvén wave heating. We assumed the presence of a broadband driver at the photosphere that launches Alfvén waves towards the prominence. An iterative method was implemented in which the energy balance equation and the Alfvén wave equation are consecutively solved. From the energy balance equation and considering no wave heating initially, we computed the equilibrium profiles along the thread of the temperature, density, ionisation fraction, and other relevant parameters. On these equilibrium profiles, we used the Alfvén wave equation to compute the wave heating rate, which was then put back in the energy balance equation to obtain new equilibrium profiles, and so on. The process was repeated until convergence to a self-consistent thread model heated by Alfvén waves was achieved. We obtained equilibrium models composed of a cold and dense thread, an extremely thin prominence-corona transition region, and an extended coronal region. We found that the length of the cold thread decreases with the temperature at the prominence core and increases with the Alfvén wave energy flux injected at the photosphere. However, computed equilibrium models for large wave energy fluxes are not possible when the wave heating rate inside the cold thread becomes larger than the radiative losses. The maximum value of the wave energy flux that allows for an equilibrium depends on the prominence core temperature. This constrains the existence of thread equilibria in realistic conditions.

Plasma diagnostics and Alfvén wave heating of solar prominences by multiwavelength observations

Abstract Solar prominences are cool and dense plasma supported by the magnetic field in the solar corona. They are composed of fine-scale structures called threads. Prominences are heated by the incident radiation from the solar atmosphere, but previous studies have shown that additional heating is necessary to maintain the temperature of prominences of about 104 K. This study aims to investigate quantitatively the mechanical heating of the prominences from observations. We performed spectroscopic observations of prominences in Hα (6563 Å), Hβ (4861 Å), and Ca ii IR (8542 Å) with the Domeless Solar Telescope at Hida observatory. The plasma parameters of the prominences are estimated by fittings of line profiles using the single-slab model and by solving the statistical equilibrium equation. By assuming that the turbulent motion is the manifestation of propagating Alfvén waves, net radiative losses and Alfvén wave energy flux in the prominences are estimated from these parameters. As a result, it was found that the energy flux by Alfvén waves is sufficient to compensate for the net radiative losses in most regions of the central part of the prominences. On the other hand, Alfvén wave energy flux tends to be insufficient at the outer part of prominences. In such regions, another heating mechanism such as enthalpy flux of mixing with coronal plasma needs to be considered.

The Formation of a U-shaped Filament Due to the Successive Magnetic Reconnection between a Filament and Its Nearby Chromospheric Fibrils

Although magnetic reconnection plays a key role in the formation of a solar filament, the detailed formation process is still ambiguous. Combining the observational data from the New Vacuum Solar Telescope and the Solar Dynamics Observatory, we analyzed the formation of a U-shaped filament via successive magnetic reconnection in the AR NOAA 11598 on 2012 October 25. The successive reconnection occurred between a filament (F) and its nearby chromospheric fibrils (CF). The associated brightening and magnetic cancellation were observed. The changes in appearance of the CF at the reconnection site were accompanied by the formation and accumulation of some new magnetic loops, as well as plasmas propagated along the formed magnetic loops from the reconnection site, indicating the changes in the topology of the F and CF. These can provide comprehensive observational evidence for successive reconnection. After the reconnection, a longer U-shaped filament was formed. During the formation of the U-shaped filament, two major magnetic energy releases took place. While in the two energy release processes, the injected plasma from the reconnection site can provide part of the material for the formation of the U-shaped filament. Therefore, we conclude that the successive reconnection results in both the dynamical evolution and the subsequent formation associated with the U-shaped filament. And the results of nonlinear force-free field extrapolation demonstrated that the magnetic topology of the F was changed significantly; this is consistent with the observational results and further confirms the formation of the U-shaped filament.

Winking filaments due to cyclic evaporation-condensation

Context. Observations have shown that some filaments appear and disappear in the Hα line wing images periodically. There have been no attempts to model these “winking filaments” thus far. Aims. The evaporation-condensation mechanism is widely used to explain the formation of solar filaments. Here, we demonstrate, for the first time, how multi-dimensional evaporation-condensation in an arcade setup invariably causes a stretching of the magnetic topology. We aim to check whether this magnetic stretching during cyclic evaporation-condensation could reproduce a winking filament. Methods. We used our open-source code MPI-AMRVAC to carry out 2D magnetohydrodynamic simulations based on a quadrupolar configuration. A periodic localized heating, which modulates the evaporation-condensation process, was imposed before, during, and after the formation of the filament. Synthetic Hα and 304 Å images were produced to compare the results with observations. Results. For the first time, we noticed the winking filament phenomenon in a simulation of the formation of on-disk solar filaments, which was in good agreement with observations. Typically, the period of the winking is different from the period of the impulsive heating. A forced oscillator model explains this difference and fits the results well. A parameter survey is also done to look into details of the magnetic stretching phenomenon. We found that the stronger the heating or the higher the layer where the heating occurs, the more significant the winking effect appears.

Solar Filament Eruptions in H α Doppler Velocity

We use observations taken with a novel solar telescope spectroheliograph to investigate the association between the early filament rise and coronal mass ejections (CMEs). The instrument allows the H α full line profile to be registered in each pixel of the solar disk with a time cadence of about 1 minute. We analyze observations of three eruptive filaments in 2021 and show that patrol telescope measurements of the H α line profile with a spectral resolution R = 40,000 can be used to detect precursors of filament eruptions with an advance of several hours and to estimate the initial acceleration of CMEs. Our limited case study also suggests that while detecting an early filament rise may serve as an indicator of a possible eruption, the filament ascent alone is not a definite sign of a CME.

An Inductively Coupled Plasma System for Investigating Spectropolarimetric Responses of Solar Plasmas to Anisotropic Fields

High precision measurements and accurate modeling of atomic polarization under three-dimensional radiation transfer are crucial to understand the structures of magnetized solar plasmas. To develop and validate spectropolarimetric measurements and analyses, we set up an inductively coupled plasma (ICP) generator designed especially for ∼1-eV plasmas interacting with radiation and weak magnetic fields. The device was put in front of the focal plane of the Horizontal Spectrograph of the Domeless Solar Telescope at Hida Observatory of Kyoto University. In helium discharges, the typical electron temperature, electron density, and helium column density of the ICP are comparable values to those of solar prominences, and the direct comparison of spectra shows almost the same opacity at He I 1083 nm. Magnetic and radiation fields were introduced to the ICP, and the system successfully reproduced reasonable spectropolarimetric signals as compared with those from the solar prominences.

Numerical simulations of prominence oscillations triggered by external perturbations

Context. Several energetic disturbances have been identified as triggers of large-amplitude oscillations (LAOs) in prominences. Observations show that Moreton or extreme ultraviolet waves excite prominence oscillations of the longitudinal, transverse, or mixed polarities. However, the mechanisms for the excitation of LAOs by these waves are not well understood. Aims. In this study, we aim to investigate mechanisms behind the triggering of LAOs via self-consistent perturbation produced by an eruption and via energetic waves coming from a distant energy source. Methods. We performed time-dependent numerical simulations in 2.5D and 2D setups, using the magnetohydrodynamic code MANCHA3D, involving a flux rope and dipped arcade magnetic configurations with an artificially loaded prominence mass in the magnetic dips. Two types of disturbances were applied to excite prominence oscillations. The first type involves perturbations produced self-consistently by an eruption, while the second type of perturbation is associated with the waves caused by an artificial energy release. Results. In the simulations of the eruption, we find that this eruption by itself does not produce LAOs in the prominence located in its vicinity. Its only effect is in inclining the magnetic configuration of the prominence. While the erupting flux rope rises, an elongated current sheet forms behind it. This current sheet becomes unstable and breaks into plasmoids. The downward-moving plasmoids cause perturbations in the velocity field by merging with the post-reconnection loops. This velocity perturbation propagates in the surroundings and enters the flux rope, causing the disturbance of the prominence mass. The analysis of the oscillatory motions of the prominence plasma reveals the excitation of small-amplitude oscillations (SAOs), which are a mixture of longitudinal and vertical oscillations with short and long periods. In the simulations with a distant artificial perturbation, a fast-mode shock wave is produced and it gradually reaches two flux rope prominences at different distances. This shock wave excites vertical LAOs as well as longitudinal SAOs with similar amplitudes, periods, and damping times in both prominences. Finally, in the experiment with the external triggering of LAOs of solar prominences by an artificial perturbation in a dipped arcade prominence model, we find that although the vector normal to the front of a fast-mode shock wave is parallel to the spine of the dipped arcade well before the contact, this wave does not excite longitudinal LAOs. When the wave front approaches the prominence, it pushes the dense plasma down, establishing vertical LAOs and motions due to compression and rarefaction along the magnetic field. Conclusions. The external triggering of prominence oscillations is a complex process that excites LAOs or SAOs of the longitudinal or transverse polarizations or a mix of both types. It is not an easy task to produce LAOs in prominences because the triggering event requires a sufficient amount of energy. The orientation of the prominence axis with respect to the driving event may play a crucial role in triggering a certain type of LAOs.

Magnetic field of solar dark filaments obtained from He i10830 Å spectropolarimetric observation

AbstractSolar filaments are dense, cool plasma clouds in the solar corona. They are supposed to be supported in a dip of the coronal magnetic field. However, the models still disagree between two types of field configuration; one is the normal polarity model proposed by Kippenhahn and Schlueter (1957, Z. Astrophys., 43, 36), and the other is the reverse polarity model proposed by Kuperus and Raadu (1974, A&A, 31, 189). To understand the mechanism that makes the filaments become unstable before eruption, it is critical to know the magnetic structure of solar filaments. We performed spectropolarimetric observation in the He i (10830 Å) line to investigate the magnetic field configuration of dark filaments. The observation was carried out with the Domeless Solar Telescope at Hida Observatory with a polarization sensitivity of 3.0 × 10−4. We obtained eight samples of filaments in a quiet region. As a result of the analysis of full Stokes profiles of filaments, we found that the field strengths were estimated as 8–35 G. By comparing the direction of the magnetic field in filaments and the global distribution of the photospheric magnetic field, we determined the magnetic field configuration of the filaments, and we concluded that one out of the eight samples has normal polarity configuration, and seven out of the eight have reverse polarity configuration.

Thermodynamic and Magnetic Topology Evolution of the X1.0 Flare on 2021 October 28 Simulated by a Data-driven Radiative Magnetohydrodynamic Model

Solar filament eruptions, flares, and coronal mass ejections (CMEs) are manifestations of drastic releases of energy in the magnetic field, which are related to many eruptive phenomena, from the Earth’s magnetosphere to black hole accretion disks. With the availability of high-resolution magnetograms on the solar surface, observational data-based modeling is a promising way to quantitatively study the underlying physical mechanisms behind observations. By incorporating thermal conduction and radiation losses in the energy equation, we develop a new data-driven radiative magnetohydrodynamic model, which has the capability of capturing the thermodynamic evolution compared to our previous zero-β model. Our numerical results reproduce the major observational characteristics of the X1.0 flare on 2021 October 28 in NOAA active region 12887, including the morphology of the eruption, the kinematics of the flare ribbons, extreme ultraviolet (EUV) radiations, and the two components of the EUV waves predicted by the magnetic stretching model, i.e., a fast-mode shock wave and a slower apparent wave, due to successive stretching of the magnetic field lines. Moreover, some intriguing phenomena are revealed in the simulation. We find that flare ribbons separate initially and ultimately stop at the outer stationary quasi-separatrix layers (QSLs). Such outer QSLs correspond to the border of the filament channel and determine the final positions of flare ribbons, which can be used to predict the size and the lifetime of a flare before it occurs. In addition, the side views of the synthesized EUV and white-light images exhibit typical three-part structures of CMEs, where the bright leading front is roughly cospatial with the nonwave component of the EUV wave, reinforcing the use of the magnetic stretching model for the slow component of EUV waves.

Simulating Rayleigh-Taylor induced magnetohydrodynamic turbulence in prominences

Aims.Solar prominences are large-scale condensations suspended against gravity within the solar atmosphere. The Rayleigh-Taylor (RT) instability is proposed to be one of the fundamental processes that lead to the generation of dynamics at many spatial and temporal scales within these long-lived, cool, and dense structures, which are located in the solar corona. We aim to study such turbulent processes using high-resolution, direct numerical simulations of solar prominences.Methods.We ran 2.5D ideal magnetohydrodynamic (MHD) simulations with the open-sourceMPI-AMRVACcode far into the nonlinear evolution of an RT instability perturbed at the prominence-corona interface. Our simulation achieves a resolution down to ∼23 km on a 2D (x, y) domain of size 30 Mm × 30 Mm. We followed the instability transitioning from a multimode linear perturbation to its nonlinear, fully turbulent state. Over the succeeding ∼25 min period, we performed a statistical analysis of the prominence at a cadence of ∼0.858 s.Results.We find that the dominant guiding component,Bz, induces coherent structure formation predominantly in the vertical velocity component,Vy, consistent with observations, indicating an anisotropic turbulence state within our prominence. We find power-law scalings in the inertial range for the velocity, magnetic, and temperature fields. The presence of intermittency is evident from the probability density functions of the field fluctuations, which depart from Gaussianity as we consider smaller and smaller scales. In exact agreement, the higher-order structure functions quantify the multi-fractality, as do different scale characteristics and the behavior between the longitudinal and transverse directions. Thus, the statistics remain consistent with conclusions from previous observational studies, enabling us to directly relate the RT instability to the turbulent characteristics found within quiescent prominences.

Manifestation of Magnetic Flux Ropes in the Structure of Solar Prominences

Manifestation of Magnetic Flux Ropes in the Structure of Solar Prominences

Formation of multiphase plasma in galactic haloes and an analogy to solar plasma

Thermal instability (TI) potentially explains the origin of cold gas in the intracluster medium (ICM), which is heated sufficiently by AGN feedback. The Hαfilaments seen in cluster cores provide strong motivation for TI. The hot (∼107K) ICM coronae allow the growth of isobaric TI. The multiphase medium (cold-dense—hot-diffuse) forms once TI saturates. However, gravitational stratification can spatially constrain TI, and thermal conduction is known to stabilize all scales below the field length (λF). In addition, the transport of energy is anisotropic along magnetic fields. Thermal conduction may further trigger gyroscale instabilities and effective reduction ofλF. However, cold gas at small scales(<λF)needs to be verified in observations. The virial temperature in galactic haloes is lower (∼106K) and opens the regime of isochoric TI. In this regime, the cooling time is typically shorter than the sound-crossing time, and large-scale isochoric clouds are rendered unstable. The linear and non-linear isochoric clouds have interesting differences which potentially lead to either fragmentation of the cloud or not. On saturation, TI produces a turbulent medium that helps mix phases and thermalize kinetic energy and thus completes a cycle of condensation and heating. Various aspects of condensation, stratified turbulence, and magnetized transport are physically identical in solar coronae but scaled down to lower luminosity (similar temperatures). We will discuss the recent progress in TI, its connection to observations, and the analogy to solar prominences.

Manifestation of Magnetic Flux Ropes in the Structure of Solar Prominences

The appearance of quiescent solar prominences most often resembles a wide curtain or a fencemade of a vertical palisade. It is hard to imagine that such a structure can be connected or even formed by amagnetic flux rope, that is, a bundle of force lines twisted into a cylindrical helix, which sometimes clearlymanifests itself in active region filaments. However, with a relatively small activation of the prominences,when the plasma composing them begins to move along the field lines, the structure of the magnetic flux ropecan be discerned. An example of a quiescent prominence is shown, in which rotational motion is observedalong helical trajectories outlining the flux rope. The rotation is clearly visible in the time-distance diagram,which is composed of narrow strips of images of the prominence along the trajectory of motion

Splitting and Reconstruction of a Solar Filament Caused by Magnetic Emergence and Reconnection

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.

Magnetic field amplification and structure formation by the Rayleigh-Taylor instability

We report our results from a set of high-resolution, two-fluid, non-linear simulations of the magnetized Rayleigh Taylor instability (RTI) at the interface between a solar prominence and the corona. These data follow results reported earlier on linear and early non-linear RTI dynamics in this environment. This paper is focused on the generation and amplification of magnetic structures by RTI. The simulations use a two-fluid model that includes collisions between neutrals and charges, including ionization and recombination, energy and momentum transfer, and frictional heating. The 2.5D magnetized RTI simulations demonstrate that in a fully developed state of RTI, a large fraction of the gravitational energy of a prominence thread can be converted into quasi-turbulent energy of the magnetic field. The RTI magnetic energy generation is further accompanied by magnetic and plasma density structure formation, including dynamic formation, break-up, and merging of current sheets and plasmoid sub-structures. The flow decoupling between neutrals and charges, as well as ionization and recombination reactions, are shown to have significant impact on the structure formation in a magnetized RTI.