Predicting the evolution of photospheric magnetic field in solar active regions using deep learning

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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Abrupt Changes of the Photospheric Magnetic Field in Active Regions and the Impulsive Phase of Solar Flares (Preprint)

10.21236/ada566133 ◽

2012 ◽

Author(s):

E. W. Cliver ◽

G. J. Petrie ◽

A. G. Ling

Keyword(s):

Magnetic Field ◽

Solar Flares ◽

Active Regions ◽

Impulsive Phase ◽

Photospheric Magnetic Field ◽

Abrupt Changes

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Numerical calculation of force-free magnetic field for solar active regions and its application to prediction of solar flares

Computer Physics Communications ◽

10.1016/0010-4655(90)90163-u ◽

1990 ◽

Vol 59 (1) ◽

pp. 139-143 ◽

Cited By ~ 2

Author(s):

Yuanzhang Lin

Keyword(s):

Magnetic Field ◽

Numerical Calculation ◽

Solar Flares ◽

Active Regions ◽

Solar Active Regions

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Filter Magnetograph Measurements at Meudon Observatory

International Astronomical Union Colloquium ◽

10.1017/s0252921100029092 ◽

1993 ◽

Vol 141 ◽

pp. 199-202

Author(s):

Audouin Dollfus ◽

Jacques Moity

Keyword(s):

Magnetic Field ◽

Transverse Magnetic Field ◽

Observational Studies ◽

Neutral Line ◽

Active Regions ◽

Transverse Magnetic ◽

Birefringent Filter ◽

Solar Active Regions

SummaryWe report observational studies of solar active regions n°6150 and n°6850 during cycle 22. Observations were carried out with a tunable monochromatic birefringent filter coupled with a line-shifter and a Stokesmeter as well as with a spectro-magnetograph, both at Meudon Observatory. AR n°6150 is typical of emerging flux regions, while AR n° 6850, with a complex preceding δ-spot, exhibits characteristic configurations of the transverse magnetic field for flaring activity: shear along the neutral line, and curvature coupled with anomalous Evershed mass motions.

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Reconstructing solar magnetic fields from historical observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935606 ◽

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.

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Solar photosphere magnetization

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935244 ◽

2020 ◽

Vol 634 ◽

pp. A40 ◽

Cited By ~ 1

Author(s):

Véronique Bommier

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Field Gradient ◽

Magnetic Field Gradient ◽

Active Regions ◽

Spectral Lines ◽

Solar Interior ◽

Solar Photosphere ◽

Total Charge ◽

Solar Active Regions

Context. A recent review shows that observations performed with different telescopes, spectral lines, and interpretation methods all agree about a vertical magnetic field gradient in solar active regions on the order of 3 G km−1, when a horizontal magnetic field gradient of only 0.3 G km−1 is found. This represents an inexplicable discrepancy with respect to the divB = 0 law. Aims. The objective of this paper is to explain these observations through the law B = μ0(H + M) in magnetized media. Methods. Magnetization is due to plasma diamagnetism, which results from the spiral motion of free electrons or charges about the magnetic field. Their usual photospheric densities lead to very weak magnetization M, four orders of magnitude lower than H. It is then assumed that electrons escape from the solar interior, where their thermal velocity is much higher than the escape velocity, in spite of the effect of protons. They escape from lower layers in a quasi-static spreading, and accumulate in the photosphere. By evaluating the magnetic energy of an elementary atom embedded in the magnetized medium obeying the macroscopic law B = μ0(H + M), it is shown that the Zeeman Hamiltonian is due to the effect of H. Thus, what is measured is H. Results. The decrease in density with height is responsible for non-zero divergence of M, which is compensated for by the divergence of H, in order to ensure div B = 0. The behavior of the observed quantities is recovered. Conclusions. The problem of the divergence of the observed magnetic field in solar active regions finally reveals evidence of electron accumulation in the solar photosphere. This is not the case of the heavier protons, which remain in lower layers. An electric field would thus be present in the solar interior, but as the total charge remains negligible, no electric field or effect would result outside the star.

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Topological changes of the photospheric magnetic field inside active regions: A prelude to flares?

Planetary and Space Science ◽

10.1016/j.pss.2004.02.006 ◽

2004 ◽

Vol 52 (10) ◽

pp. 937-943 ◽

Cited By ~ 15

Author(s):

Luca Sorriso-Valvo ◽

Vincenzo Carbone ◽

Pierluigi Veltri ◽

Valentina I. Abramenko ◽

Alain Noullez ◽

...

Keyword(s):

Magnetic Field ◽

Active Regions ◽

Photospheric Magnetic Field ◽

Topological Changes

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Solar flare forecasting model using 3D magnetic field data

10.5194/egusphere-egu2020-13298 ◽

2020 ◽

Author(s):

Xin Huang

Keyword(s):

Magnetic Field ◽

Deep Learning ◽

Solar Flare ◽

Solar Flares ◽

Field Data ◽

Active Regions ◽

Forecasting Model ◽

Magnetic Field Data ◽

The Magnetic Field

Solar flares originate from the release of the energy stored in the magnetic field of solar active regions. Generally, the photospheric magnetograms of active regions are used as the input of the solar flare forecasting model. However, solar flares are considered to occur in the low corona. Therefore, the role of 3D magnetic field of active regions in the solar flare forecast should be explored. We extrapolate the 3D magnetic field using the potential model for all the active regions during 2010 to 2017, and then the deep learning method is applied to extract the precursors of solar flares in the 3D magnetic field data. We find that the 3D magnetic field of active regions is helpful to build a deep learning based forecasting model.

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Axial dipole moments of solar active regions in cycles 21-24

10.5194/egusphere-egu2020-21663 ◽

2020 ◽

Author(s):

Iiro Virtanen ◽

Ilpo Virtanen ◽

Alexei Pevtsov ◽

Kalevi Mursula

Keyword(s):

Magnetic Field ◽

Dipole Moment ◽

Magnetic Flux ◽

Opposite Sign ◽

Dipole Moments ◽

Active Regions ◽

Photospheric Magnetic Field ◽

Axial Dipole ◽

Axial Moment ◽

Cycle 24

The axial dipole moments of emerging active regions control the evolution of the axial dipole moment of the whole photospheric magnetic field and the strength of polar fields. Hale's and Joy's laws of polarity and tilt orientation affect the sign of the axial dipole moment of an active region, determining the normal sign for each solar cycle. If both laws are valid (or both violated), the sign of the axial moment is normal. However, for some active regions, only one of the two laws is violated, and the signs of these axial dipole moments are the opposite of normal. The opposite-sign axial dipole moments can potentially have a significant effect on the evolution of the photospheric magnetic field, including the polar fields.We determine the axial dipole moments of active regions identified from magnetographic observations and study how the axial dipole moments of normal and opposite signs are distributed in time and latitude in solar cycles 21-24.We use active regions identified from the synoptic maps of the photospheric magnetic field measured at the National Solar Observatory (NSO) Kitt Peak (KP) observatory, the Synoptic Optical Long term Investigations of the Sun (SOLIS) vector spectromagnetograph (VSM), and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO).We find that, typically, some 30% of active regions have opposite-sign axial dipole moments in every cycle, often making more than 20% of the total axial dipole moment. Most opposite-signed moments are small, but occasional large moments, which can affect the evolution of polar fields on their own, are observed. Active regions with such a large opposite-sign moment may include only a moderate amount of total magnetic flux. We find that in cycles 21-23 the northern hemisphere activates first and shows emergence of magnetic flux over a wider latitude range, while the southern hemisphere activates later, and emergence is concentrated to lower latitudes. We also note that cycle 24 differs from cycles 21-23 in many ways. Cycle 24 is the only cycle where the northern butterfly wing includes more active regions than the southern wing, and where axial dipole moment of normal sign emerges on average later than opposite-signed axial dipole moment. The total axial dipole moment and even the average axial moment of active regions is smaller in cycle 24 than in previous cycles.

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