scholarly journals THE INFLUENCE OF THE MAGNETIC FIELD ON RUNNING PENUMBRAL WAVES IN THE SOLAR CHROMOSPHERE

2013 ◽  
Vol 779 (2) ◽  
pp. 168 ◽  
Author(s):  
D. B. Jess ◽  
V. E. Reznikova ◽  
T. Van Doorsselaere ◽  
P. H. Keys ◽  
D. H. Mackay
Keyword(s):  
Magnetic Field ◽  
Solar Chromosphere ◽  
The Magnetic Field

scholarly journals Joint Discussion 3 Solar active regions and 3D magnetic structure

2006 ◽  
Vol 2 (14) ◽  
pp. 139-168
Author(s):  
Debi Prasad Choudhary ◽  
Michal Sobotka
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Large Scale ◽  
Focal Point ◽  
Active Regions ◽  
Theoretical Modelling ◽  
Solar Chromosphere ◽  
Origin And Evolution ◽  
Solar Active Regions ◽  
The Magnetic Field

AbstractKeeping in view of the modern powerful observing tools, among othersHinode(formerlySOLAR-B),STEREOand Frequency-Agile Solar Radiotelescope, and sophisticated modelling techniques, Joint Discussion 3 during the IAU General Assembly 2006 focused on the properties of magnetic field of solar active regions starting in deep interior of the Sun, from where they buoyantly rise to the coronal heights where the site of most explosive events are located. Intimately related with the active regions, the origin and evolution of the magnetic field of quiet Sun, the large scale chromospheric structures were also the focal point of the Joint Discussion. The theoretical modelling of the generation and dynamics of magnetic field in solar convective zone show that the interaction of the magnetic field with the Coriolis force and helical turbulent convection results in the tilts and twists in the emerging flux. In the photosphere, some of these fluxes appear in sunspots with field strengths up to about 6100 G. Spectro-polarimetric measurements reveal that the line of sight velocities and magnetic field of these locations are found to be uncombed and depend on depth in the atmosphere and exhibit gradients or discontinuities. The inclined magnetic fields beyond penumbra appear as moving magnetic features that do not rise above upper photospheric heights. As the flux rises, the solar chromosphere is the most immediate and intermediary layer where competitive magnetic forces begin to dominate their thermodynamic counterparts. The magnetic field at these heights is now measured using several diagnostic lines such as CaII854.2 nm, HI656.3 nm, and HeI1083.0 nm. The radio observations show that the coronal magnetic field of post flare loops are of the order of 30 G, which might represent the force-free magnetic state of active region in the corona. The temperatures at these coronal heights, derived from the line widths, are in the range from 2.4 to 3.7 million degree. The same line profile measurements indicate the existence of asymmetric flows in the corona. The theoretical extrapolation of photospheric field into coronal heights and their comparison with the observations show that there exists a complex topology with separatrices associated to coronal null points. The interaction of these structures often lead to flares and coronal mass ejections. The current MHD modelling of active region field shows that for coronal mass ejection both local active region magnetic field and global magnetic field due to the surrounding magnetic flux are important. Here, we present an extended summary of the papers presented in Joint Discussion 03 and open questions related to the solar magnetic field that are likely to be the prime issue with the modern observing facilities such asHinodeandSTEREOmissions.

Numerical modelling of MHD waves in the solar chromosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 395-404 ◽  
Author(s):  
Mats Carlsson ◽  
Thomas J Bogdan
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
Mode Conversion ◽  
Three Dimensions ◽  
Mhd Waves ◽  
Solar Chromosphere ◽  
Fast Mode ◽  
Reflected Waves ◽  
The Waves ◽  
The Magnetic Field

Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30° much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low–mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.

scholarly journals Solar image denoising with convolutional neural networks

2019 ◽  
Vol 629 ◽  
pp. A99 ◽  
Author(s):  
C. J. Díaz Baso ◽  
J. de la Cruz Rodríguez ◽  
S. Danilovic
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spatial Coherence ◽  
Principal Component ◽  
Real Data ◽  
Spectral Lines ◽  
Solar Chromosphere ◽  
Weak Signals ◽  
Statistical Characterization ◽  
The Magnetic Field

The topology and dynamics of the solar chromosphere are greatly affected by the presence of magnetic fields. The magnetic field can be inferred by analyzing polarimetric observations of spectral lines. Polarimetric signals induced by chromospheric magnetic fields are, however, particularly weak, and in most cases very close to the detection limit of current instrumentation. Because of this, there are only few observational studies that have successfully reconstructed the three components of the magnetic field vector in the chromosphere. Traditionally, the signal-to-noise ratio of observations has been improved by performing time-averages or spatial averages, but in both cases, some information is lost. More advanced techniques, like principal-component analysis, have also been employed to take advantage of the sparsity of the observations in the spectral direction. In the present study, we use the spatial coherence of the observations to reduce the noise using deep-learning techniques. We designed a neural network that is capable of recovering weak signals under a complex noise corruption (including instrumental artifacts and non-linear post-processing). The training of the network is carried out without a priori knowledge of the clean signals, or an explicit statistical characterization of the noise or other corruption. We only use the same observations as our generative model. The performance of this method is demonstrated on both synthetic experiments and real data. We show examples of the improvement in typical signals obtained in current telescopes such as the Swedish 1 m Solar Telescope. The presented method can recover weak signals equally well no matter what spectral line or spectral sampling is used. It is especially suitable for cases when the wavelength sampling is scarce.

scholarly journals Intermediate shock sub-structures within a slow-mode shock occurring in partially ionised plasma

2019 ◽  
Vol 626 ◽  
pp. A46 ◽  
Author(s):  
B. Snow ◽  
A. Hillier
Keyword(s):  
Magnetic Field ◽  
Initial Conditions ◽  
Frictional Heating ◽  
Physical Parameters ◽  
Solar Chromosphere ◽  
Finite Width ◽  
Slow Mode ◽  
Wide Range ◽  
Intermediate Shock ◽  
The Magnetic Field

Context. Slow-mode shocks are important in understanding fast magnetic reconnection, jet formation and heating in the solar atmosphere, and other astrophysical systems. The atmospheric conditions in the solar chromosphere allow both ionised and neutral particles to exist and interact. Under such conditions, fine sub-structures exist within slow-mode shocks due to the decoupling and recoupling of the plasma and neutral species. Aims. We study numerically the fine sub-structure within slow-mode shocks in a partially ionised plasma, in particular, analysing the formation of an intermediate transition within the slow-mode shock. Methods. High-resolution 1D numerical simulations were performed using the (PIP) code using a two-fluid approach. Results. We discover that long-lived intermediate (Alfvén) shocks can form within the slow-mode shock, where there is a shock transition from above to below the Alfvén speed and a reversal of the magnetic field across the shock front. The collisional coupling provides frictional heating to the neutral fluid, resulting in a Sedov-Taylor-like expansion with overshoots in the neutral velocity and neutral density. The increase in density results in a decrease of the Alfvén speed and with this the plasma inflow is accelerated to above the Alfvén speed within the finite width of the shock leading to the intermediate transition. This process occurs for a wide range of physical parameters and an intermediate shock is present for all investigated values of plasma-β, neutral fraction, and magnetic angle. As time advances the magnitude of the magnetic field reversal decreases since the neutral pressure cannot balance the Lorentz force. The intermediate shock is long-lived enough to be considered a physical structure, independent of the initial conditions. Conclusions. Intermediate shocks are a physical feature that can exist as shock sub-structure for long periods of time in partially ionised plasma due to collisional coupling between species.

scholarly journals Spectropolarimetric NLTE inversion code SNAPI

2018 ◽  
Vol 617 ◽  
pp. A24 ◽  
Author(s):  
I. Milić ◽  
M. van Noort
Keyword(s):  
Magnetic Field ◽  
Model Atmosphere ◽  
Field Vector ◽  
Spectral Lines ◽  
Local Thermal Equilibrium ◽  
Solar Chromosphere ◽  
Atmospheric Parameters ◽  
Academic Problem ◽  
Specific Implementation ◽  
The Magnetic Field

Context. Inversion codes are computer programs that fit a model atmosphere to the observed Stokes spectra, thus retrieving the relevant atmospheric parameters. The rising interest in the solar chromosphere, where spectral lines are formed by scattering, requires developing, testing, and comparing new non-local thermal equilibrium (NLTE) inversion codes. Aims. We present a new NLTE inversion code that is based on the analytical computation of the response functions. We named the code SNAPI, which is short for spectropolarimetic NLTE analytically powered inversion. Methods. SNAPI inverts full Stokes spectrum in order to obtain a depth-dependent stratification of the temperature, velocity, and the magnetic field vector. It is based on the so-called node approach, where atmospheric parameters are free to vary in several fixed points in the atmosphere, and are assumed to behave as splines in between. We describe the inversion approach in general and the specific choices we have made in the implementation. Results. We test the performance on one academic problem and on two interesting NLTE examples, the Ca II 8542 and Na I D spectral lines. The code is found to have excellent convergence properties and outperforms a finite-difference based code in this specific implementation by at least a factor of three. We invert synthetic observations of Na lines from a small part of a simulated solar atmosphere and conclude that the Na lines reliably retrieve the magnetic field and velocity in the range −3 <  logτ <  −0.5.

scholarly journals Radio Measurements of the Magnetic Field in the Solar Chromosphere and the Corona

2021 ◽  
Vol 7 ◽  
Author(s):  
Costas E. Alissandrakis ◽  
Dale E. Gary
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Quantitative Information ◽  
Solar Chromosphere ◽  
Magnetic Field Effects ◽  
Collisionless Plasmas ◽  
Radio Measurements ◽  
Magnetic Filed ◽  
Future Work ◽  
The Magnetic Field

The structure of the upper solar atmosphere, on all observable scales, is intimately governed by the magnetic field. The same holds for a variety of solar phenomena that constitute solar activity, from tiny transient brightening to huge Coronal Mass Ejections. Due to inherent difficulties in measuring magnetic field effects on atoms (Zeeman and Hanle effects) in the corona, radio methods sensitive to electrons are of primary importance in obtaining quantitative information about its magnetic field. In this review we explore these methods and point out their advantages and limitations. After a brief presentation of the magneto-ionic theory of wave propagation in cold, collisionless plasmas, we discuss how the magnetic field affects the radio emission produced by incoherent emission mechanisms (free-free, gyroresonance, and gyrosynchrotron processes) and give examples of measurements of magnetic filed parameters in the quiet sun, active regions and radio CMEs. We proceed by discussing how the inversion of the sense of circular polarization can be used to measure the field above active regions. Subsequently we pass to coherent emission mechanisms and present results of measurements from fiber bursts, zebra patterns, and type II burst emission. We close this review with a discussion of the variation of the magnetic field, deduced by radio measurements, from the low corona up to ~ 10 solar radii and with some thoughts about future work.

scholarly journals An optimization principle for computing stationary MHD equilibria with solar wind flow

2020 ◽  
Author(s):  
Thomas Wiegelmann ◽  
Thomas Neukirch ◽  
Dieter Nickeler ◽  
Iulia Chifu
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Magnetic Field ◽  
Field Vector ◽  
Source Surface ◽  
Solar Chromosphere ◽  
Wind Flow ◽  
Solar Wind Flow ◽  
Nonlinear Force ◽  
The Magnetic Field

&lt;p&gt;Knowledge about the magnetic field and plasma environment is important&lt;br&gt;for almost all physical processes in the solar atmosphere. Precise&lt;br&gt;measurements of the magnetic field vector are done routinely only in&lt;br&gt;the photosphere, e.g. by SDO/HMI. These measurements are used as&lt;br&gt;boundary condition for modelling the solar chromosphere and corona,&lt;br&gt;whereas some model assumptions have to be made. In the low-plasma-beta&lt;br&gt;corona the Lorentz-force vanishes and the magnetic field&lt;br&gt;is reconstructed with a nonlinear force-free model. In the mixed-beta&lt;br&gt;chromosphere plasma forces have to be taken into account with the&lt;br&gt;help of a magnetostatic model. And finally for modelling the global&lt;br&gt;corona far beyond the source surface the solar wind flow has to&lt;br&gt;be incorporated within a stationary MHD model.&lt;br&gt;To do so, we generalize a nonlinear force-free and magneto-static optimization&lt;br&gt;code by the inclusion of a field aligned compressible plasma flow.&lt;br&gt;Applications are the implementation of the solar wind on&lt;br&gt;global scale. This allows to reconstruct the coronal magnetic field further&lt;br&gt;outwards than with potential field, nonlinear force-free and magneto-static models.&lt;br&gt;This way the model might help in future to provide the magnetic connectivity&lt;br&gt;for joint observations of remote sensing and in-situ instruments on Solar&lt;br&gt;Orbiter and Parker Solar Probe.&lt;/p&gt;

scholarly journals Topological model of the anemone microflares in the solar chromosphere

2019 ◽  
Vol 623 ◽  
pp. L4
Author(s):  
Yu. V. Dumin ◽  
B. V. Somov
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Spatial Scales ◽  
Solar Chromosphere ◽  
Transient Phenomena ◽  
Sufficient Detail ◽  
Complex Transformation ◽  
Ribbon Structure ◽  
Ribbon Structures ◽  
The Magnetic Field

Context. The chromospheric anemone microflares, which were discovered by Hinode satellite about a decade ago, are specific transient phenomena starting from a few luminous ribbons on the chromospheric surface and followed by an eruption upward. While the eruptive stage was studied in sufficient detail, a quantitative theory of formation of the initial multi-ribbon structure remains undeveloped until now. Aims. We construct a sufficiently simple but general model of the magnetic field sources that is able to reproduce all the observed types of luminous ribbons by varying only a single parameter. Methods. As a working tool, we employed the Gorbachev–Kel’ner–Somov–Shvarts (GKSS) model of the magnetic field, which was originally suggested about three decades ago to explain fast ignition of the magnetic reconnection over considerable spatial scales by tiny displacements of the magnetic sources. Quite unexpectedly, this model turns out to be efficient for the description of generic multi-ribbon structures in the anemone flares as well. Results. As follows from our numerical simulation, displacement of a single magnetic source (sunspot) with respect to three other sources results in a complex transformation from three to four ribbons and then again to three ribbons, but with an absolutely different arrangement. Such structures closely resemble the observed patterns of emission in the anemone microflares.

Observing the galactic magnetic field

1967 ◽  
Vol 31 ◽  
pp. 375-380
Author(s):  
H. C. van de Hulst
Keyword(s):  
Magnetic Field ◽  
Fair Agreement ◽  
Solar Neighbourhood ◽  
Galactic Magnetic Field ◽  
The Magnetic Field

Various methods of observing the galactic magnetic field are reviewed, and their results summarized. There is fair agreement about the direction of the magnetic field in the solar neighbourhood:l= 50° to 80°; the strength of the field in the disk is of the order of 10-5gauss.

Sign in / Sign up

Export Citation Format

Share Document