Here we review the recent progress made in the detection, examination, characterisation and interpretation of oscillations manifesting in small-scale magnetic elements in the solar photosphere. This region of the Sun's atmosphere is especially dynamic, and importantly, permeated with an abundance of magnetic field concentrations. Such magnetic features can span diameters of hundreds to many tens of thousands of km, and are thus commonly referred to as the `building blocks' of the magnetic solar atmosphere. However, it is the smallest magnetic elements that have risen to the forefront of solar physics research in recent years. Structures, which include magnetic bright points, are often at the diffraction limit of even the largest of solar telescopes. Importantly, it is the improvements in facilities, instrumentation, imaging techniques and processing algorithms during recent years that have allowed researchers to examine the motions, dynamics and evolution of such features on the smallest spatial and temporal scales to date. It is clear that while these structures may demonstrate significant magnetic field strengths, their small sizes make them prone to the buffeting supplied by the ubiquitous surrounding convective plasma motions. Here, it is believed that magnetohydrodynamic waves can be induced, which propagate along the field lines, carrying energy upwards to the outermost extremities of the solar corona. Such wave phenomena can exist in a variety of guises, including fast and slow magneto-acoustic modes, in addition to Alfven waves. Coupled with rapid advancements in magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly investigate how wave motion is generated in the solar photosphere, which oscillatory modes are most prevalent, and the role that these waves play in supplying energy to various layers of the solar atmosphere.
We investigate the generation mechanisms of MHD Poynting flux in the magnetised solar photosphere. Using radiative MHD modelling of the solar photosphere with initial magnetic configurations that differ in their field strength and geometry, we show the presence of two different mechanisms for MHD Poynting flux generation in simulations of solar photospheric magneto-convection. The weaker mechanism is connected to vertical transport of weak horizontal magnetic fields in the convectively stable layers of the upper photosphere, while the stronger is the production of Poynting flux in strongly mag…
It is well known that magnetic fields dominate the dynamics in the solar corona, and new generation of numerical modelling of the evolution of coronal magnetic fields, as featured with boundary conditions driven directly by observation data, are being developed. This paper describes a new approach of data-driven magnetohydrodynamic (MHD) simulation of solar active region (AR) magnetic field evolution, which is for the first time that a data-driven full-MHD model utilizes directly the photospheric velocity field from DAVE4VM. We constructed a well-established MHD equilibrium based on a single v…
Data-driven simulation is becoming an important approach for realistically characterizing the configuration and evolution of solar active regions, revealing the onset mechanism of solar eruption events and hopefully achieving the goal of accurate space weather forecast, which is beyond the scope of any existing theoretical modelling. Here we performed a full 3D MHD simulation using the data-driven approach and followed the whole evolution process from quasi-static phase to eruption successfully for solar active region NOAA 11429. The MHD system was driven at the bottom boundary by photospheric…
Jet phenomena with a bright loop in their footpoint, called anemone jets, have been observed in the solar corona and chromosphere. These jets are formed as a consequence of magnetic reconnection, and from the scale universality of magnetohydrodynamics (MHD), it can be expected that anemone jets exist even in the solar photosphere. However, it is not necessarily apparent that jets can be generated as a result of magnetic reconnection in the photosphere, where the magnetic energy is not dominant. Furthermore, MHD waves generated from the photospheric jets could contribute to chromospheric heatin…
By focusing on the oscillations of the cross-sectional area and the intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Capturing several series of high-resolution images of pores and sunspots and employing wavelet analysis in conjunction with empirical mode decomposition (EMD) makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as representative examples of MHD waveguides in the lower solar atmosphere. The sunspots and pore display a range of…
High-resolution observations of the solar photosphere have identified a wide variety of spiralling motions in the solar plasma. These spirals vary in properties, but are observed to be abundant at the solar surface. In this work these spirals are studied for their potential as magnetohydrodynamic (MHD) wave generation mechanisms. The inter-granular lanes, where these spirals are commonly observed, are also regions where the magnetic field strength is higher than average. This combination of magnetic field and spiralling plasma is a recipe for the generation of Alfvén waves and other MHD waves.…
Magnetic flux tubes reaching from the solar convective zone into the chromosphere have to pass through the relatively cool, and therefore non-ideal (i.e. resistive) photospheric region enclosed between the highly ideal sub-photospheric and chromospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of photospheric material into the flux tube and a deviation from iso-rotation along the tube axis. This means that there is a difference in angular velocity of the plasma flow inside the tube below and above the non-ideal r…
Before using 3D MHD simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112 and…
Torsional motions are ubiquitous in the solar atmosphere. In this work, we perform 3D numerical simulations which mimic a vortex-type photospheric driver with a Gaussian spatial profile. This driver is implemented to excite MHD waves in an axially symmetric, 3D magnetic flux tube embedded in a realistic solar atmosphere. The Gaussian width of the driver is varied and the resulting perturbations are compared. Velocity vectors were decomposed into parallel, perpendicular and azimuthal components with respect to pre-defined magnetic flux surfaces. These components correspond broadly to the fast, …
In this study we explore the possibility of simplifying the modeling of magnetohydrodynamic (MHD) slow body modes observed in photospheric magnetic structure such as the umbrae of sunspots and pores. The simplifying approach assumes that the variation of the eigenvalues of slow body waves can be derived by imposing that the longitudinal component of velocity with respect to the tube axis is zero at the boundary of the magnetic flux tube, which is in a good agreement with observations. To justify our approach we compare the results of our simplified model for slow body modes in cylindrical flux…
We study extreme-ultraviolet emission line spectra derived from three-dimensional magnetohydrodynamic models of structures in the corona. In order to investigate the effects of increased magnetic activity at photospheric levels in a numerical experiment, a much higher magnetic flux density is applied at photospheric levels as compared to the Sun. Thus, we can expect our results to highlight the differences between the Sun and more active, but still solar-like stars. We discuss signatures seen in extreme-ultraviolet emission lines synthesized from these models and compare them to signatures fou…
The presence of magneto-acoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magneto-acoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope (DOT) and Rapid Oscillations in the Solar Atmosphere (ROSA) instruments, we captured two series of high-resolution intensity images with short cadence of two isolated magn…
Quantifying coronal magnetic field remains a central problem in solar physics. Nowadays the coronal magnetic field is often modelled using nonlinear force-free field (NLFFF) reconstructions, whose accuracy has not yet been comprehensively assessed. Here we perform a detailed casting of the NLFFF reconstruction tools, such as pi-disambiguation, photospheric field preprocessing, and volume reconstruction methods using a 3D snapshot of the publicly available full-fledged radiative MHD model. Specifically, from the MHD model we know the magnetic field vector in the entire 3D domain, which enables …
We studied bright umbral dots (UDs) detected in a moderate size sunspot and compared their statistical properties to recent MHD models. The study is based on high resolution data recorded by the New Solar Telescope at the Big Bear Solar Observatory and 3D MHD simulations of sunspots. Observed UDs, living longer than 150 s, were detected and tracked in a 46 min long data set, using an automatic detection code. Total 1553 (620) UDs were detected in the photospheric (low chromospheric) data. Our main findings are: i) none of the analyzed UDs is precisely circular, ii) the diameter-intensity relat…
Bright points (BPs) in the solar photosphere are radiative signatures of magnetic elements described by slender flux tubes located in the darker intergranular lanes. They contribute to the ultraviolet (UV) flux variations over the solar cycle and hence may influence the Earth's climate. Here we combine high-resolution UV and spectro-polarimetric observations of BPs by the SUNRISE observatory with 3D radiation MHD simulations. Full spectral line syntheses are performed with the MHD data and a careful degradation is applied to take into account all relevant instrumental effects of the observatio…
We performed two data-based magnetohydrodynamic (MHD) simulations for solar active region 12371 which produced an M6.5 flare. The first simulation is a full data-driven simulation where the initial condition is given by a nonlinear force-free field (NLFFF). This NLFFF was extrapolated from photospheric magnetograms approximately 1 hour prior to the flare, and then a time-varying photospheric magnetic field is imposed at the bottom surface. The second simulation is also a data-driven simulation, but it stops driving at the bottom before the time of flare onset and then switches to the data-cons…
Coronal Non-Thermal and Doppler Plasma Flows Driven by Photospheric Flux in 28 Active Regions
University College London, Mullard Space Science Laboratory（伦敦大学学院，穆拉德空间科学实验室）；University of Vienna, Institute of Astrophysics（维也纳大学，天体物理研究所）；Computational Physics, Inc.（计算物理公司）；Space Science Division, Naval Research Laboratory（海军研究实验室空间科学部）；NASA Goddard Space Flight Center, Solar Physics Laboratory, Heliophysics Science Division（美国国家航空航天局戈达德太空飞行中心，太阳物理学实验室，日球物理科学部）；Department of Mathematics, Physics and Electrical Engineering, Northumbria University（诺森比亚大学数学、物理与电气工程系）；INAF Osservatorio Astronomico di Roma（意大利国家天体物理研究所罗马天文台）
The magnetic line ratio (MLR) method has been extensively used in the measurement of photospheric magnetic field strength. It was devised for the neutral iron line pair at 5247.1 A and 5250.2 A (5250 A pair). Other line pairs as well-suited as this pair been have not been reported in the literature. The aim of the present work is to identify new line pairs useful for the MLR technique and to test their reliability. We use a three dimensional magnetohydrodynamic (MHD) simulation representing the quiet Sun atmosphere to synthesize the Stokes profiles. Then, we apply the MLR technique to the Stok…
Downflows on the solar surface are suspected to play a major role in the dynamics of the convection zone. We investigate the existence of the long-lasting downflows whose effects influence the interior of the Sun and the outer layers. We study the sets of Dopplergrams and magnetograms observed with SDO and Hinode spacecrafts and a MHD simulation. All of the aligned sequences, which were corrected from the satellite motions and tracked with the differential rotation, were used to detect the long-lasting downflows in the quiet-Sun at the disc centre. To learn about the structure of the flows bel…
We investigate the linear correlation coefficient between the intensities at different wavelengths in photospheric and chromospheric spectral lines. Waves that propagate vertically through the stratified solar atmosphere affect different wavelengths at different times. This leads to a characteristic pattern of (non-)coherence of the intensity at various wavelengths. We derived the correlation matrices for several photospheric and chromospheric spectral lines from observations. For comparison with the observations, we calculate correlation matrices for spectra from LTE modeling approaches, 1-D …
Four different approximate approaches used to model the stressing of coronal magnetic fields due to an imposed photospheric motion are compared with each other and the results from a full time-dependent magnetohydrodynamic (MHD) code. The assumptions used for each of the approximate methods are tested by considering large photospheric footpoint displacements. We consider a simple model problem, comparing the full nonlinear magnetohydrodynamic evolution, determined with the Lare2D numerical code, with four approximate approaches. Two of these, magneto-frictional relaxation and a quasi-1D Grad-S…
The Parker hypothesis (Parker (1972)) assumes that heating of coronal loops occurs due to reconnection, induced when photospheric motions braid field lines to the point of current sheet formation. In this contribution we address the question of how the nature of photospheric motions affects heating of braided coronal loops. We design a series of boundary drivers and quantify their properties in terms of complexity and helicity injection. We examine a series of long-duration full resistive MHD simulations in which a simulated coronal loop, consisting of initially uniform field lines, is subject…
Solar flares and plasma eruptions are sudden releases of magnetic energy stored in the plasma atmosphere. To understand the physical mechanisms governing their occurrences, three-dimensional magnetic fields from the photosphere up to the corona must be studied. The solar photospheric magnetic fields are observable, whereas the coronal magnetic fields cannot be measured. One method for inferring coronal magnetic fields is performing data-driven simulations, which involves time-series observational data of the photospheric magnetic fields with the bottom boundary of magnetohydrodynamic simulatio…
MHD wave propagation inside the Sun's atmosphere is closely related to the magnetic field topology. For example, magnetic fields are able to lower the cutoff frequency for acoustic waves thus allowing waves which would otherwise be trapped below the photosphere to propagate into the upper atmosphere. Another example is that MHD waves can be transmitted or converted into other forms of waves at altitudes where the sound speed equals the Alfvén speed. We take advantage of the large field-of-view provided by the IBIS experiment to study the wave propagation at two heights in the solar atmosphere,…
Models for the evolution of the solar coronal magnetic field are vital for understanding solar activity, yet the best measurements of magnetic field lie at the photosphere, necessitating the development of coronal models which are \textit{"data-driven"} at the photosphere. We present an investigation to determine the feasibility and accuracy of such methods. Our validation framework uses a simulation of active region (AR) formation, modeling the emergence of magnetic flux from the convection zone to the corona, as a ground-truth dataset, to supply both the photospheric information, and to perf…
We present observational evidence for the presence of MHD waves in the solar photosphere deduced from SOHO/MDI Dopplergram velocity observations. The magneto-acoustic perturbations are observed as acoustic power enhancement in the sunspot umbra at high-frequency bands in the velocity component perpendicular to the magnetic field. We use numerical modelling of wave propagation through localised non-uniform magnetic field concentration along with the same filtering procedure as applied to the observations to identify the observed waves. Guided by the results of the numerical simulations we class…
In this review, our present day understanding of the Sun's global photospheric and coronal magnetic fields is discussed from both observational and theoretical viewpoints. Firstly, the large-scale properties of photospheric magnetic fields are described, along with recent advances in photospheric magnetic flux transport models. Following this, the wide variety of theoretical models used to simulate global coronal magnetic fields are described. From this, the combined application of both magnetic flux transport simulations and coronal modeling techniques to describe the phenomena of coronal hol…
Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigen-mode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the Ohmic …
We perform a number of numerical simulations of the solar corona with the aim to understand how it responds to different conditions in the photosphere. By changing parameters which govern the motion of the plasma at the photosphere we study the behavior of the corona, in particular, the effects on the current density generated. An MHD code is used to run simulations, using a 20x20x20 Mm^3 box with time spans ranging from one hundred to several hundreds of minutes. All the experiments show a fast initial increase of the current density, followed by a stabilization around an asymptotic value whi…
We have performed a three-dimensional magnetohydrodynamic simulation to study the emergence of a twisted magnetic flux tube from -20,000 km of the solar convection zone to the corona through the photosphere and the chromosphere. The middle part of the initial tube is endowed with a density deficit to instigate a buoyant emergence. As the tube approaches the surface, it extends horizontally and makes a flat magnetic structure due to the photosphere ahead of the tube. Further emergence to the corona breaks out via the interchange-mode instability of the photospheric fields, and eventually severa…
We investigate the dynamics of a closed corona cartesian reduced magnetohydrodynamic (MHD) model where photospheric vortices twist the coronal magnetic field lines. We consider two corotating or counter-rotating vortices localized at the center of the photospheric plate, and additionally more corotating vortices that fill the plate entirely. Our investigation is specifically devoted to study the fully nonlinear stage, after the linear stage during which the vortices create laminar and smoothly twisting flux tubes. Our main goal is to understand the dynamics of photospheric vortices twisting th…
MHD simulations of sunspots have successfully reproduced many aspects of sunspot fine structure as consequence of magneto convection in inclined magnetic field. We study how global sunspot properties and penumbral fine structure depend on the magnetic top boundary condition as well as on grid spacing. The overall radial extent of the penumbra is subject to the magnetic top boundary condition. All other aspects of sunspot structure and penumbral fine structure are resolved at an acceptable level starting from a grid resolution of 48 [24] km (horizontal [vertical]). We find that the amount of in…
There is a recurring question in solar physics about whether or not electric currents are neutralized in active regions (ARs). This question was recently revisited using three-dimensional (3D) magnetohydrodynamic (MHD) numerical simulations of magnetic flux emergence into the solar atmosphere. Such simulations showed that flux emergence can generate a substantial net current in ARs. Another source of AR currents are photospheric horizontal flows. Our aim is to determine the conditions for the occurrence of net vs. neutralized currents with this second mechanism. Using 3D MHD simulations, we sy…
Using numerical simulations of the magnetised solar photosphere and radiative diagnostics of the simulated photospheric models, we further analyse the physical nature of magnetic photospheric intergranular vortices. We confirm the magnetic nature of the vortices and find that most MHD Umov-Poynting flux is produced by horizontal vortex motions in the magnetised intergranular lanes. In addition, we consider possible ways to directly observe photospheric magnetic vortices using spectropolarimetry. Although horizontal plasma motions cannot be detected in the spectropolarimetric observations of so…
A nonlinear force-free field (NLFFF) extrapolation is widely used to reconstruct the three-dimensional magnetic field in the solar corona from the observed photospheric magnetic field. However, the pressure gradient and gravitational forces are ignored in the NLFFF model, even though the photospheric and chromospheric magnetic fields are not in general force-free. Here we develop a magnetohydrodynamic (MHD) relaxation method that reconstructs the solar atmospheric (chromospheric and coronal) magnetic field as a non-force-free magnetic field (NFFF) in magnetohydrostatic equilibrium where the Lo…
Using the spectroscopic imaging capabilities of the Swedish Solar Telescope, we aim to provide the first investigation on the nature and dynamics of elongated absorption features (fibrils) observed in H$α$ in the internetwork. We observe and identify a number of internetwork fibrils, which form away from the kilogauss, network magnetic flux, and we provide a synoptic view on their behaviour. The internetwork fibrils are found to support wave-like behaviour, which we interpret as Magnetohydrodynamic (MHD) kink waves. The properties of these waves, that is, amplitude, period, and propagation spe…
The variation in area of quiet magnetic network measured over the sunspot cycle should modulate the spatially averaged photospheric temperature gradient, since temperature declines with optical depth more gradually in magnetic flux tube atmospheres. Yet, limb darkening measurements show no dependence upon activity level, even at an rms precision of 0.04%. We study the sensitivity of limb darkening to changes in area filling factor using a 3D MHD model of the magnetized photosphere. The limb darkening change expected from the measured 11 yr area variation lies below the level of measured limb d…
To understand the nonlinear dynamics of the Parker scenario for coronal heating, long-time high-resolution simulations of the dynamics of a coronal loop in cartesian geometry are carried out. A loop is modeled as a box extended along the direction of the strong magnetic field $B_0$ in which the system is embedded. At the top and bottom plates, which represent the photosphere, velocity fields mimicking photospheric motions are imposed. We show that the nonlinear dynamics is described by different regimes of MHD anisotropic turbulence, with spectra characterized by intertial range power laws who…
We present a new global model of the solar corona, including the low corona, the transition region and the top of chromosphere. The realistic 3D magnetic field is simulated using the data from the photospheric magnetic field measurements. The distinctive feature of the new model is incorporating the MHD Alfven wave turbulence. We assume this turbulence and its non-linear dissipation to be the only momentum and energy source for heating the coronal plasma and driving the solar wind. The difference between the turbulence dissipation efficiency in coronal holes and that in closed field regions is…
We investigate the vertical gradient of the magnetic field of sunspots in the photospheric layer. Independent observations were obtained with the SOT/SP onboard the Hinode spacecraft and with the TIP-2 mounted at the VTT. We apply state-of-the-art inversion techniques to both data sets to retrieve the magnetic field and the corresponding vertical gradient. In the sunspot penumbrae we detected patches of negative vertical gradients of the magnetic field strength, i.e.,the magnetic field strength decreases with optical depth in the photosphere. The negative gradient patches are located in the in…
Since only the magnetic conditions at the photosphere can be routinely observed in current observations, it is of great significance to find out the influences of photospheric magnetic conditions on solar eruptive activities. Previous studies about catastrophe indicated that the magnetic system consisting of a flux rope in a partially open bipolar field is subject to catastrophe, but not if the bipolar field is completely closed under the same specified photospheric conditions. In order to investigate the influence of the photospheric magnetic conditions on the catastrophic behavior of this sy…
The Parker or field line tangling model of coronal heating is investigated through long-time high-resolution simulations of the dynamics of a coronal loop in cartesian geometry within the framework of reduced magnetohydrodynamics (RMHD). Slow photospheric motions induce a Poynting flux which saturates by driving an anisotropic turbulent cascade dominated by magnetic energy and characterized by current sheets elongated along the axial magnetic field. Increasing the value of the axial magnetic field different regimes of MHD turbulence develop with a bearing on coronal heating rates. In physical …
We have performed MHD simulations of Alfven wave propagation along an open flux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photospheric granular motion from G-band movies of Hinode/SOT. It is shown that the total energy flux at the corona becomes larger and the transition region height becomes higher in the case when we use the observed spectrum rather than white/pink noise spectrum as the wave generator. This difference can be explained by the Alfven wav…
Current magnetohydrodynamic (MHD) simulations of the initiation of solar eruptions are still commonly carried out with idealized magnetic field models, whereas the realistic coronal field prior to eruptions can possibly be reconstructed from the observable photospheric field. Using a nonlinear force-free field extrapolation prior to a sigmoid eruption in AR 11283 as the initial condition in a MHD model, we successfully simulate the realistic initiation process of the eruption event, as is confirmed by a remarkable resemblance to the SDO/AIA observations. Analysis of the pre-eruption field reve…
The goal of this study is to explore a novel method for the solar photospheric magnetic field diagnostics using Stokes V widths of different magnetosensitive Fe~I spectral lines. We calculate Stokes I and V profiles of several Fe I lines based on a one-dimensional photospheric model VAL C using the NICOLE radiative transfer code. These profiles are used to produce calibration curves linking the intrinsic magnetic field values with the widths of blue peaks of Stokes V profiles. The obtained calibration curves are then tested using the Stokes profiles calculated for more realistic photospheric m…
Force-freeness of a solar magnetic field is a key to reconstructing invisible coronal magnetic structure of an emerging flux region on the Sun where active phenomena such as flares and coronal mass ejections frequently occur. We have performed magnetohydrodynamic (MHD) simulations which are adjusted to investigate force-freeness of an emerging magnetic field by using the virial theorem. Our focus is on how the force-free range of an emerging flux region develops and how it depends on the twist of a pre-emerged magnetic field. As an emerging flux region evolves, the upper limit of the force-fre…
Magnetic helicity quantifies how globally sheared and/or twisted is the magnetic field in a volume. This quantity is believed to play a key role in solar activity due to its conservation property. Helicity is continuously injected into the corona during the evolution of active regions (ARs). To better understand and quantify the role of magnetic helicity in solar activity, the distribution of magnetic helicity flux in ARs needs to be studied. The helicity distribution can be computed from the temporal evolution of photospheric magnetograms of ARs such as the ones provided by SDO/HMI and Hinode…
We study structure and dynamics of the turbulent photospheric magnetic field in the active region NOAA 11158 by characterizing the spatial and temporal scaling properties of the line-of-sight (LOS) component. Using high-resolution high-cadence LOS magnetograms from SDO/HMI, we measured power-law exponents $α$ and $β$ describing wavenumber- ($k$) and frequency-domain ($f$) Fourier power spectra, respectively, and investigated their evolution during the passage of the active region through the field of view of HMI. Flaring active region NOAA 11158 produces an average one-dimensional spatial powe…
Solar eruptions are the most powerful drivers of space weather. To understand their cause and nature, it is crucial to know how the coronal magnetic field evolves before eruption. Here we study the formation process of a relatively large-scale magnetic flux rope (MFR) in active region NOAA~12371 that erupts with a major flare and coronal mass ejection on 2015 June 21. A data-driven numerical magnetohydrodynamic model is employed to simulate three-dimensional coronal magnetic field evolution of one-day duration before the eruption. Comparison between the observed features and our modeled magnet…
Solar flares are energetic events taking place in the Sun's atmosphere, and their effects can greatly impact the environment of the surrounding planets. In particular, eruptive flares, as opposed to confined flares, launch coronal mass ejections into the interplanetary medium, and as such, are one of the main drivers of space weather. After briefly reviewing the main characteristics of solar flares, we summarize the processes that can account for the build up and release of energy during their evolution. In particular, we focus on the development of recent 3D numerical simulations that explain…
An exospheric kinetic solar wind model is interfaced with an observation-driven single fluid magnetohydrodynamic (MHD) model. Initially, a photospheric magnetogram serves as observational input in the fluid approach to extrapolate the heliospheric magnetic field. Then semi-empirical coronal models are used for estimating the plasma characteristics up to a heliocentric distance of 0.1AU. From there on a full MHD model which computes the three-dimensional time-dependent evolution of the solar wind macroscopic variables up to the orbit of the Earth is used. After interfacing the density and veloc…
Bright small-scale magnetic elements found mainly in intergranular lanes at the solar surface are named bright points (BPs). They show high contrasts in Fraunhofer G-band observations and are described by nearly vertical slender flux tubes or sheets. A recent comparison between BP observations in the ultraviolet (UV) and visible spectral range recorded with the balloon-borne observatory SUNRISE and state-of-the-art magnetohydrodynamical (MHD) simulations revealed a kiloGauss magnetic field for 98% of the synthetic BPs. Here we address the opposite question, namely which fraction of pixels host…
