scholarly journals Stratification of canopy magnetic fields in a plage region

2020 ◽  
Vol 642 ◽  
pp. A210
Author(s):  
Roberta Morosin ◽  
Jaime de la Cruz Rodríguez ◽  
Gregal J. M. Vissers ◽  
Rahul Yadav
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Numerical Models ◽  
Lower Boundary ◽  
Field Approximation ◽  
Weak Field ◽  
Field Vector ◽  
Plage Region ◽  
The Magnetic Field

Context. The role of magnetic fields in the chromospheric heating problem remains greatly unconstrained. Most theoretical predictions from numerical models rely on a magnetic configuration, field strength, and connectivity; the details of which have not been well established with observational studies for many chromospheric scenarios. High-resolution studies of chromospheric magnetic fields in plage are very scarce or non existent in general. Aims. Our aim is to study the stratification of the magnetic field vector in plage regions. Previous studies predict the presence of a magnetic canopy in the chromosphere that has not yet been studied with full-Stokes observations. We use high-spatial resolution full-Stokes observations acquired with the CRisp Imaging Spectro-Polarimeter (CRISP) at the Swedish 1-m Solar Telescope in the Mg I 5173 Å, Na I 5896 Å and Ca II 8542 Å lines. Methods. We have developed a spatially-regularized weak-field approximation (WFA) method, based on the idea of spatial regularization. This method allows for a fast computation of magnetic field maps for an extended field of view. The fidelity of this new technique has been assessed using a snapshot from a realistic 3D magnetohydrodynamics simulation. Results. We have derived the depth-stratification of the line-of-sight component of the magnetic field from the photosphere to the chromosphere in a plage region. The magnetic fields are concentrated in the intergranular lanes in the photosphere and expand horizontally toward the chromosphere, filling all the space and forming a canopy. Our results suggest that the lower boundary of this canopy must be located around 400 − 600 km from the photosphere. The mean canopy total magnetic field strength in the lower chromosphere (z ≈ 760 km) is 658 G. At z = 1160 km, we estimate ⟨B∥⟩ ≈ 417 G. Conclusions. In this study we propose a modification to the WFA that improves its applicability to data with a worse signal-to-noise ratio. We have used this technique to study the magnetic properties of the hot chromospheric canopy that is observed in plage regions. The methods described in this paper provide a quick and reliable way of studying multi layer magnetic field observations without the many difficulties inherent to other inversion methods.

scholarly journals Temporal evolution of short-lived penumbral microjets

2020 ◽  
Vol 642 ◽  
pp. A128
Author(s):  
A. L. Siu-Tapia ◽  
L. R. Bellot Rubio ◽  
D. Orozco Suárez ◽  
R. Gafeira
Keyword(s):  
Magnetic Field ◽  
Temporal Evolution ◽  
Spectral Characteristics ◽  
Field Approximation ◽  
Weak Field ◽  
Field Vector ◽  
Magnetic Field Vector ◽  
Maximum Brightness ◽  
Time Variations ◽  
The Magnetic Field

Context. Penumbral microjets (PMJs) is the name given to elongated jet-like brightenings observed in the chromosphere above sunspot penumbrae. They are transient events that last from a few seconds to several minutes, and their origin is presumed to be related to magnetic reconnection processes. Previous studies have mainly focused on their morphological and spectral characteristics, and more recently on their spectropolarimetric signals during the maximum brightness stage. Studies addressing the temporal evolution of PMJs have also been carried out, but they are based on spatial and spectral time variations only. Aims. Here we investigate, for the first time, the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere. Methods. We use fast-cadence spectropolarimetric observations of the Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA) is used to estimate the strength and inclination of the magnetic field vector. By separating the Ca II 854.2 nm line into two different wavelength domains to account for the chromospheric origin of the line core and the photospheric contribution to the wings, we infer the height variation of the magnetic field vector. Results. The WFA reveals larger magnetic field changes in the upper photosphere than in the chromosphere during the PMJ maximum brightness stage. In the photosphere, the magnetic field inclination and strength undergo a transient increase for most PMJs, but in 25% of the cases the field strength decreases during the brightening. In the chromosphere, the magnetic field tends to be slightly stronger during the PMJs. Conclusions. The propagation of compressive perturbation fronts followed by a rarefaction phase in the aftershock region may explain the observed behavior of the magnetic field vector. The fact that such behavior varies among the analyzed PMJs could be a consequence of the limited temporal resolution of the observations and the fast-evolving nature of the PMJs.

scholarly journals Ubiquitous hundred-Gauss magnetic fields in solar spicules

2020 ◽  
Vol 642 ◽  
pp. A61
Author(s):  
M. Kriginsky ◽  
R. Oliver ◽  
N. Freij ◽  
D. Kuridze ◽  
A. Asensio Ramos ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Fields ◽  
Field Approximation ◽  
Weak Field ◽  
Field Polarity ◽  
Statistical Point ◽  
Quiet Sun ◽  
Solar Spicules ◽  
The Magnetic Field

Aims. We aim to study the magnetic field in solar spicules using high-resolution spectropolarimetric observations in the Ca II 8542 Å line obtained with the Swedish 1-m Solar Telescope. Methods. The equations that result from the application of the weak field approximation (WFA) to the radiative transfer equations were used to infer the line-of-sight (LOS) component of the magnetic field (BLOS). Two restrictive conditions were imposed on the Stokes I and V profiles at each pixel before they could be used in a Bayesian inversion to compute its BLOS. Results. The LOS magnetic field component was inferred in six data sets totalling 448 spectral scans in the Ca II 8542 Å line and containing both active region and quiet Sun areas, with values of hundreds of Gauss being abundantly inferred. There seems to be no difference, from a statistical point of view, between the magnetic field strength of spicules in the quiet Sun or near an active region. On the other hand, the BLOS distributions present smaller values on the disc than off-limb, a fact that can be explained by the effect of superposition on the chromosphere of on-disc structures. We show that on-disc pixels in which the BLOS is determined are possibly associated with spicular structures because these pixels are co-spatial with the magnetic field concentrations at the network boundaries and the sign of their BLOS agrees with that of the underlying photosphere. We find that spicules in the vicinity of a sunspot have a magnetic field polarity (i.e. north or south) equal to that of the sunspot. This paper also contains an analysis of the effect of off-limb overlapping structures on the observed Stokes I and V parameters and the BLOS obtained from the WFA. It is found that this value is equal to or smaller than the largest LOS magnetic field components of the two structures. In addition, using random BLOS, Doppler velocities, and line intensities of these two structures leads in ≃50% of the cases to Stokes I and V parameters that are unsuitable to be used with the WFA. Conclusions. Our results present a scarcity of LOS magnetic field components smaller than some 50 G, which must not be taken as evidence against the existence of these magnetic field strengths in spicules. This fact possibly arises as the consequence of signal superposition and noise in the data. We also suggest that the failure of previous works to infer the strong magnetic fields in spicules detected here is their coarser spatial and/or temporal resolution.

scholarly journals Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 Å line

2020 ◽  
Vol 644 ◽  
pp. A43 ◽  
Author(s):  
A. G. M. Pietrow ◽  
D. Kiselman ◽  
J. de la Cruz Rodríguez ◽  
C. J. Díaz Baso ◽  
A. Pastor Yabar ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Numerical Models ◽  
Signal To Noise Ratio ◽  
Field Configuration ◽  
Magnetic Field Configuration ◽  
Signal To Noise ◽  
Plage Region ◽  
Noise Ratio ◽  
The Magnetic Field

Context. It has so far proven impossible to reproduce all aspects of the solar plage chromosphere in quasi-realistic numerical models. The magnetic field configuration in the lower atmosphere is one of the few free parameters in such simulations. The literature only offers proxy-based estimates of the field strength, as it is difficult to obtain observational constraints in this region. Sufficiently sensitive spectro-polarimetric measurements require a high signal-to-noise ratio, spectral resolution, and cadence, which are at the limit of current capabilities. Aims. We use critically sampled spectro-polarimetric observations of the Ca II 8542 Å line obtained with the CRISP instrument of the Swedish 1-m Solar Telescope to study the strength and inclination of the chromospheric magnetic field of a plage region. This will provide direct physics-based estimates of these values, which could aid modelers to put constraints on plage models. Methods. We increased the signal-to-noise ratio of the data by applying several methods including deep learning and PCA. We estimated the noise level to be 1 × 10−3 Ic. We then used STiC, a non-local thermodynamic equilibrium inversion code to infer the atmospheric structure and magnetic field pixel by pixel. Results. We are able to infer the magnetic field strength and inclination for a plage region and for fibrils in the surrounding canopy. In the plage we report an absolute field strength of |B| = 440 ± 90 G, with an inclination of 10° ±16° with respect to the local vertical. This value for |B| is roughly double of what was reported previously, while the inclination matches previous studies done in the photosphere. In the fibrillar region we found |B| = 300 ± 50 G, with an inclination of 50° ±13°.

scholarly journals Forward modelling of MHD waves in braided magnetic fields

2020 ◽  
Vol 643 ◽  
pp. A86
Author(s):  
L. E. Fyfe ◽  
T. A. Howson ◽  
I. De Moortel
Keyword(s):  
Magnetic Field ◽  
Kinetic Energy ◽  
Magnetic Fields ◽  
Numerical Models ◽  
Lower Boundary ◽  
Mhd Waves ◽  
Doppler Velocity ◽  
Forward Modelling ◽  
The Waves ◽  
The Magnetic Field

Aims. We investigate synthetic observational signatures generated from numerical models of transverse waves propagating in complex (braided) magnetic fields. Methods. We consider two simulations with different levels of magnetic field braiding and impose periodic, transverse velocity perturbations at the lower boundary. As the waves reflect off the top boundary, a complex pattern of wave interference occurs. We applied the forward modelling code FoMo and analysed the synthetic emission data. We examined the line intensity, Doppler shifts, and kinetic energy along several line-of-sight (LOS) angles. Results. The Doppler shift perturbations clearly show the presence of the transverse (Alfvénic) waves. However, in the total intensity, and running difference, the waves are less easily observed for more complex magnetic fields and may be indistinguishable from background noise. Depending on the LOS angle, the observable signatures of the waves reflect some of the magnetic field braiding, particularly when multiple emission lines are available, although it is not possible to deduce the actual level of complexity. In the more braided simulation, signatures of phase mixing can be identified. We highlight possible ambiguities in the interpretation of the wave modes based on the synthetic emission signatures. Conclusions. Most of the observables discussed in this article behave in the manner expected, given knowledge of the evolution of the parameters in the 3D simulations. Nevertheless, some intriguing observational signatures are present. Identifying regions of magnetic field complexity is somewhat possible when waves are present; although, even then, simultaneous spectroscopic imaging from different lines is important in order to identify these locations. Care needs to be taken when interpreting intensity and Doppler velocity signatures as torsional motions, as is done in our setup. These types of signatures are a consequence of the complex nature of the magnetic field, rather than real torsional waves. Finally, we investigate the kinetic energy, which was estimated from the Doppler velocities and is highly dependent on the polarisation of the wave, the complexity of the background field, and the LOS angles.

scholarly journals The magnetic field in the dense photodissociation region of DR 21

2020 ◽  
Author(s):  
Atanu Koley ◽  
Nirupam Roy ◽  
Karl M Menten ◽  
Arshia M Jacob ◽  
Thushara G S Pillai ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Zeeman Effect ◽  
Zeeman Splitting ◽  
Weak Field ◽  
Field Energy ◽  
Evolutionary Stage ◽  
Maser Emission ◽  
The Magnetic Field ◽  
Photodissociation Region

Abstract Measuring interstellar magnetic fields is extremely important for understanding their role in different evolutionary stages of interstellar clouds and of star formation. However, detecting the weak field is observationally challenging. We present measurements of the Zeeman effect in the 1665 and 1667 MHz (18 cm) lines of the hydroxyl radical (OH) lines toward the dense photodissociation region (PDR) associated with the compact H ii region DR 21 (Main). From the OH 18 cm absorption, observed with the Karl G. Jansky Very Large Array, we find that the line of sight magnetic field in this region is ∼0.13 mG. The same transitions in maser emission toward the neighbouring DR 21(OH) and W 75S-FR1 regions also exhibit the Zeeman splitting. Along with the OH data, we use [C ii] 158 μm line and hydrogen radio recombination line data to constrain the physical conditions and the kinematics of the region. We find the OH column density to be ∼3.6 × 1016(Tex/25 K) cm−2, and that the 1665 and 1667 MHz absorption lines are originating from the gas where OH and C+ are co-existing in the PDR. Under reasonable assumptions, we find the measured magnetic field strength for the PDR to be lower than the value expected from the commonly discussed density–magnetic field relation while the field strength values estimated from the maser emission are roughly consistent with the same. Finally, we compare the magnetic field energy density with the overall energetics of DR 21’s PDR and find that, in its current evolutionary stage, the magnetic field is not dynamically important.

scholarly journals Magnetic Field Instability of a Plasma in a Beam of Electromagnetic Radiation

1980 ◽  
Vol 35 (4) ◽  
pp. 461-463 ◽  
Author(s):  
O. M. Gradov ◽  
L. Stenflo
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Magnetic Fields ◽  
Field Strength ◽  
Electromagnetic Radiation ◽  
Characteristic Time ◽  
Incident Radiation ◽  
Maximum Value ◽  
Quasi Stationary State ◽  
The Magnetic Field

Abstract A beam of electromagnetic radiation can generate magnetic fields in plasmas. It is shown that those fields grow significantly when the incident radiation is sufficiently strong. We obtain expressions for the characteristic time of the growth of the fields as well as for their spatial distribution and point out a possible mechanism, which can lead to the formation of a quasi-stationary state. The maximum value of the magnetic field strength is estimated

Magnetic fields end-face effect investigation of HTS bulk over PMG with 3D-modeling numerical method

2015 ◽  
Vol 29 (25n26) ◽  
pp. 1542041
Author(s):  
Yujie Qin ◽  
Yiyun Lu
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Numerical Method ◽  
3D Modeling ◽  
Field Vector ◽  
Vector Method ◽  
Hts Bulk ◽  
Levitation System ◽  
Electromagnetic Behavior ◽  
The Magnetic Field

In this paper, the magnetic fields end-face effect of high temperature superconducting (HTS) bulk over a permanent magnetic guideway (PMG) is researched with 3D-modeling numerical method. The electromagnetic behavior of the bulk is simulated using finite element method (FEM). The framework is formulated by the magnetic field vector method (H-method). A superconducting levitation system composed of one rectangular HTS bulk and one infinite long PMG is successfully investigated using the proposed method. The simulation results show that for finite geometrical HTS bulk, even the applied magnetic field is only distributed in [Formula: see text]–[Formula: see text] plane, the magnetic field component Hz which is along the [Formula: see text]-axis can be observed interior the HTS bulk.

scholarly journals Chromospheric observations and magnetic configuration of a supergranular structure

2018 ◽  
Vol 621 ◽  
pp. A1 ◽  
Author(s):  
Carolina Robustini ◽  
Sara Esteban Pozuelo ◽  
Jorrit Leenaarts ◽  
Jaime de la Cruz Rodríguez
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Velocity Distribution ◽  
Field Approximation ◽  
Weak Field ◽  
Line Of Sight ◽  
Weak Field Approximation ◽  
Field Lines ◽  
Unipolar Region ◽  
The Magnetic Field

Context.Unipolar magnetic regions are often associated with supergranular cells. The chromosphere above these regions is regulated by the magnetic field, but the field structure is poorly known. In unipolar regions, the fibrillar arrangement does not always coincide with magnetic field lines, and polarimetric observations are needed to establish the chromospheric magnetic topology.Aims.In an active region close to the limb, we observed a unipolar annular network of supergranular size. This supergranular structure harbours a radial distribution of the fibrils converging towards its centre. We aim to improve the description of this structure by determining the magnetic field configuration and the line-of-sight velocity distribution in both the photosphere and the chromosphere.Methods.We observed the supergranular structure at different heights by taking data in the Fe I6301–6302 Å, Hα, Ca II8542 Å, and the Ca IIH&K spectral lines with the CRisp Imaging SpectroPolarimeter (CRISP) and CHROMospheric Imaging Spectrometer (CHROMIS) at the Swedish 1-m Solar Telescope. We performed Milne-Eddington inversions of the spectropolarimetric data of Fe I6301–6302 Å and applied the weak field approximation to Ca II8542 Å data to retrieve the magnetic field in the photosphere and chromosphere. We used photospheric magnetograms of CRISP, Hinode Solar Optical Telescope spectropolarimeter, and Helioseismic and Magnetic Imager to calculate the magnetic flux. We investigated the velocity distribution using the line-of-sight velocities computed from the Milne-Eddington inversion and from the Doppler shift of theK3feature in the Ca IIK spectral line. To describe the typical spectral profiles characterising the chromosphere above the inner region of the supergranular structure, we performed aK-mean clustering of the spectra in Ca IIK.Results.The photospheric magnetic flux shows that the supergranular boundary has an excess of positive polarity and the whole structure is not balanced. The magnetic field vector at chromospheric heights, retrieved by the weak field approximation, indicates that the field lines within the supergranular cell tend to point inwards, and might form a canopy above the unipolar region. In the centre of the supergranular cell hosting the unipolar region, we observe a persistent chromospheric brightening coinciding with a strong gradient in the line-of-sight velocity.

A portable apparatus for measuring the magnetic field strength in an electromagnetic wave

1931 ◽  
Vol 27 (3) ◽  
pp. 481-489
Author(s):  
L. G. Vedy ◽  
A. F. Wilkins
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Wave ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Special Means ◽  
Portable Apparatus ◽  
The Magnetic Field ◽  
Field Strengths

A portable apparatus is described which is capable of measuring directly, by means of a loop aerial, the magnetic field in an electromagnetic wave. Accurate measurements are possible of magnetic fields corresponding to field strengths of 0·2 millivolts per metre. Special means of providing small known calibrating E. M. F. S are described. The apparatus can be used to measure signals over the range 6 microvolts to 300 millivolts. Used in conjunction with a small portable vertical aerial, field strengths down to 2 microvolts per metre can be measured.

scholarly journals Fast downflows in a chromospheric filament

2019 ◽  
Vol 15 (S354) ◽  
pp. 454-457
Author(s):  
K. Sowmya ◽  
A. Lagg ◽  
S. K. Solanki ◽  
J. S. Castellanos Durán
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Fields ◽  
Velocity Component ◽  
Field Vector ◽  
Line Of Sight ◽  
Plasma Velocity ◽  
Supersonic Velocities ◽  
Slow Velocity ◽  
The Magnetic Field

AbstractAn active region filament in the upper chromosphere is studied using spectropolarimetric data in He i 10830 Å from the GREGOR telescope. A Milne-Eddingon based inversion of the Unno-Rachkovsky equations is used to retrieve the velocity and the magnetic field vector of the region. The plasma velocity reaches supersonic values closer to the feet of the filament barbs and coexist with a slow velocity component. Such supersonic velocities result from the acceleration of the plasma as it drains from the filament spine through the barbs. The line-of-sight magnetic fields have strengths below 200 G in the filament spine and in the filament barbs where fast downflows are located, their strengths range between 100 - 700 G.

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