An atlas of photospheric magnetic field observations and computed coronal magnetic fields: 1976?1985

Solar Physics ◽  
1986 ◽  
Vol 105 (1) ◽  
pp. 205-211 ◽  
Author(s):  
J. Todd Hoeksema ◽  
Philip H. Scherrer
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Photospheric Magnetic Field ◽  
Field Observations ◽  
Coronal Magnetic Fields

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

scholarly journals Reconstructing solar magnetic fields from historical observations

2019 ◽  
Vol 627 ◽  
pp. A11
Author(s):  
I. O. I. Virtanen ◽  
I. I. Virtanen ◽  
A. A. Pevtsov ◽  
L. Bertello ◽  
A. Yeates ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Long Term Evolution ◽  
Photospheric Magnetic Field ◽  
Solar Magnetic Fields ◽  
Term Evolution ◽  
Large Scale Field

Aims. The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations. Methods. We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975−1985 in order to test and validate our method. Results. The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field.

scholarly journals Computing nonlinear force free coronal magnetic fields

2003 ◽  
Vol 10 (4/5) ◽  
pp. 313-322 ◽  
Author(s):  
T. Wiegelmann ◽  
T. Neukirch
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Random Noise ◽  
Coronal Magnetic Field ◽  
Optimization Method ◽  
Numerical Code ◽  
Coronal Magnetic Fields ◽  
Nonlinear Force ◽  
Free Fields

Abstract. Knowledge of the structure of the coronal magnetic field is important for our understanding of many solar activity phenomena, e.g. flares and CMEs. However, the direct measurement of coronal magnetic fields is not possible with present methods, and therefore the coronal field has to be extrapolated from photospheric measurements. Due to the low plasma beta the coronal magnetic field can usually be assumed to be approximately force free, with electric currents flowing along the magnetic field lines. There are both observational and theoretical reasons which suggest that at least prior to an eruption the coronal magnetic field is in a nonlinear force free state. Unfortunately the computation of nonlinear force free fields is way more difficult than potential or linear force free fields and analytic solutions are not generally available. We discuss several methods which have been proposed to compute nonlinear force free fields and focus particularly on an optimization method which has been suggested recently. We compare the numerical performance of a newly developed numerical code based on the optimization method with the performance of another code based on an MHD relaxation method if both codes are applied to the reconstruction of a semi-analytic nonlinear force-free solution. The optimization method has also been tested for cases where we add random noise to the perfect boundary conditions of the analytic solution, in this way mimicking the more realistic case where the boundary conditions are given by vector magnetogram data. We find that the convergence properties of the optimization method are affected by adding noise to the boundary data and we discuss possibilities to overcome this difficulty.

scholarly journals Magnetic Field Reconstruction in a Solar Active Region

2001 ◽  
Vol 203 ◽  
pp. 328-330
Author(s):  
H. Wang ◽  
Y. Yan ◽  
T. Sakurai
Keyword(s):  
Magnetic Field ◽  
Integral Equation ◽  
Active Region ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Numerical Technique ◽  
Boundary Integral ◽  
Field Reconstruction ◽  
Coronal Magnetic Fields ◽  
Function Vector

Supposing coronal magnetic fields are in a force-free state from the chromosphere to the height of two solar radii, we reconstruct 3D force-free magnetic fields by making use of a new numerical technique, in which the fields are represented by a boundary integral equation based on a specific Green's function. Vector magnetic fields observed on the photospheric surface can be taken as the boundary conditions of this equation. Magnetic fields in AR8270 on 14 July 1998 were employed as an example to exhibit the capability of this numerical technique.

scholarly journals Estimation of Magnetic Field Strength from Enhanced Solar Radio Emission

1994 ◽  
Vol 47 (6) ◽  
pp. 811 ◽  
Author(s):  
SBSS Sarma
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radio Emission ◽  
Solar Radio ◽  
Active Regions ◽  
Shock Velocity ◽  
Solar Radio Emission ◽  
Type I ◽  
Radio Noise ◽  
Coronal Magnetic Fields

The manifestation of solar activity on radio noise records at 28.6 MHz is discussed with special emphasis on Type-I noise storms and the associated coronal magnetic fields above the active regions in time. Magnetic fields are estimated, assuming that the Type-I radio emission at decametre wavelengths is due to shock waves, by making use of the observed shock velocity. The results are comparable with the existing estimates.

scholarly journals Solar Magnetic Fields in Association With Flares

1971 ◽  
Vol 43 ◽  
pp. 359-366 ◽  
Author(s):  
R. Michard
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Empirical Evidence ◽  
Time Scale ◽  
Photospheric Magnetic Field ◽  
Solar Magnetic Fields ◽  
Magnetic Structures ◽  
Field Patterns

The association of Hα flares with photospheric magnetic field patterns is reviewed on the basis of empirical evidence. The insertion of flares in the H∥ and H⊥ patterns is described. Present data on the evolution of magnetic structures in connection with flares suggest that flares result from special trends in this evolution leading to stressed and/or ‘misconnected’ fields. However no sudden changes with a flare-like time scale have been definitely observed in photospheric fields.

scholarly journals A Study on Correcting the Effect of Polarization Crosstalk in Full-Disk Solar Photospheric Magnetic Field Observations

Solar Physics ◽  
2022 ◽  
Vol 297 (1) ◽  
Author(s):  
S. Liu ◽  
J. T. Su ◽  
X. Y. Bai ◽  
Y. Y. Deng ◽  
J. Chen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Photospheric Magnetic Field ◽  
Field Observations ◽  
Full Disk

scholarly journals Magnetism and the Invisible Man: The mysteries of coronal cavities

2013 ◽  
Vol 8 (S300) ◽  
pp. 139-146 ◽  
Author(s):  
Sarah Gibson
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Interplanetary Space ◽  
Three Dimensional ◽  
Field Measurements ◽  
Coronal Magnetic Field ◽  
Magnetic Structures ◽  
Coronal Magnetic Fields ◽  
Multiple Wavelengths ◽  
The Magnetic Field

AbstractMagnetism defines the complex and dynamic solar corona. Twists and tangles in coronal magnetic fields build up energy and ultimately erupt, hurling plasma into interplanetary space. These coronal mass ejections (CMEs) are transient riders on the ever-outflowing solar wind, which itself possesses a three-dimensional morphology shaped by the global coronal magnetic field. Coronal magnetism is thus at the heart of any understanding of the origins of space weather at the Earth. However, we have historically been limited by the difficulty of directly measuring the magnetic fields of the corona, and have turned to observations of coronal plasma to trace out magnetic structure. This approach is complicated by the fact that plasma temperatures and densities vary among coronal magnetic structures, so that looking at any one wavelength of light only shows part of the picture. In fact, in some regimes it is the lack of plasma that is a significant indicator of the magnetic field. Such a case is the coronal cavity: a dark, elliptical region in which strong and twisted magnetism dwells. I will elucidate these enigmatic features by presenting observations of coronal cavities in multiple wavelengths and from a variety of observing vantages, including unprecedented coronal magnetic field measurements now being obtained by the Coronal Multichannel Polarimeter (CoMP). These observations demonstrate the presence of twisted magnetic fields within cavities, and also provide clues to how and why cavities ultimately erupt as CMEs.

scholarly journals Photospheric and coronal magnetic fields in six magnetographs

2019 ◽  
Vol 626 ◽  
pp. A67 ◽  
Author(s):  
Ilpo Virtanen ◽  
Kalevi Mursula
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Solar Corona ◽  
Source Surface ◽  
Scaling Factors ◽  
Solar Cycle Variation ◽  
Coronal Magnetic Fields ◽  
Resolution Data

Context. Solar photospheric magnetic fields have been observed since the 1950s and calibrated digital data are available from the 1970s onwards. Synoptic maps of the photospheric magnetic field are widely used in solar research, especially in the modeling of the solar corona and solar wind, and in studies of space weather and space climate. Magnetic flux density of the solar corona is a key parameter for heliospheric physics. Aims. The observed photospheric magnetic flux depends on the instrument and data processing used, which is a major problem for long-term studies. Here we scale the different observations of the photospheric field to the same absolute level and form a uniform record of coronal magnetic flux since the 1970s. Methods. We use a recently suggested method of harmonic scaling, which scales any pair of synoptic observations of any resolution to the same level. After scaling, we use the Potential Field Source Surface (PFSS) model to calculate the scaled magnetic field at various altitudes from photosphere to coronal source surface. Results. Harmonic scaling gives effective, latitudinally dependent scaling factors, which vary over the solar cycle. When scaling low-resolution data to high-resolution data, effective scaling factors are typically largest at low latitudes in the ascending phase of solar cycle and smallest for unipolar polar fields around solar minima. The harmonic scaling method used here allows for the observations of the different data sets to be scaled to the same level and the scaled unsigned coronal flux densities agree very well with each other. We also find that scaled coronal magnetic fields show a slightly different solar cycle variation from that of the nonscaled fields.

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