Photospheric Magnetic Field Properties of Flaring versus Flare‐quiet Active Regions. I. Data, General Approach, and Sample Results

2003 ◽  
Vol 595 (2) ◽  
pp. 1277-1295 ◽  
Author(s):  
K. D. Leka ◽  
G. Barnes
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Photospheric Magnetic Field

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

2004 ◽  
Vol 52 (10) ◽  
pp. 937-943 ◽  
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

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

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

<p>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.</p><p>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).</p><p>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.</p>

scholarly journals Two-dipole model of the asymmetric Sun

2020 ◽  
Vol 10 ◽  
pp. 40
Author(s):  
Bertalan Zieger ◽  
Kalevi Mursula
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Dipole Moments ◽  
Active Regions ◽  
Opposite Polarity ◽  
Heliospheric Current Sheet ◽  
Dipole Model ◽  
Photospheric Magnetic Field ◽  
Photospheric Field ◽  
Even Harmonics

The large-scale photospheric magnetic field is commonly thought to be mainly dipolar during sunspot minima, when magnetic fields of opposite polarity cover the solar poles. However, recent studies show that the octupole harmonics contribute comparably to the spatial power of the photospheric field at these times. Also, the even harmonics are non-zero, indicating that the Sun is hemispherically asymmetric with systematically stronger fields in the south during solar minima. We present here an analytical model of two eccentric axial dipoles of different strength, which is physically motivated by the dipole moments produced by decaying active regions. With only four parameters, this model closely reproduces the observed large-scale photospheric field and all significant coefficients of its spherical harmonics expansion, including the even harmonics responsible for the solar hemispheric asymmetry. This two-dipole model of the photospheric magnetic field also explains the southward shift of the heliospheric current sheet observed during recent solar minima.

scholarly journals A New Parameter of the Photospheric Magnetic Field to Distinguish Eruptive-flare Producing Solar Active Regions

2020 ◽  
Vol 894 (1) ◽  
pp. 20
Author(s):  
Pei Hsuan Lin ◽  
Kanya Kusano ◽  
Daikou Shiota ◽  
Satoshi Inoue ◽  
K. D. Leka ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Active Regions ◽  
Photospheric Magnetic Field ◽  
Solar Active Regions

scholarly journals Reconstructing solar magnetic fields from historical observations

2018 ◽  
Vol 616 ◽  
pp. A134 ◽  
Author(s):  
I. O. I. Virtanen ◽  
I. I. Virtanen ◽  
A. A. Pevtsov ◽  
K. Mursula
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Active Regions ◽  
Surface Flux ◽  
Magnetic Activity ◽  
Maunder Minimum ◽  
Photospheric Magnetic Field ◽  
Sunspot Activity

Aims. Sunspot activity is often hemispherically asymmetric, and during the Maunder minimum, activity was almost completely limited to one hemisphere. In this work, we use surface flux simulation to study how magnetic activity limited only to the southern hemisphere affects the long-term evolution of the photospheric magnetic field in both hemispheres. The key question is whether sunspot activity in one hemisphere is enough to reverse the polarity of polar fields in both hemispheres. Methods. We simulated the evolution of the photospheric magnetic field from 1978 to 2016 using the observed active regions of the southern hemisphere as input. We studied the flow of magnetic flux across the equator and its subsequent motion towards the northern pole. We also tested how the simulated magnetic field is changed when the activity of the southern hemisphere is reduced. Results. We find that activity in the southern hemisphere is enough to reverse the polarity of polar fields in both hemispheres by the cross-equatorial transport of magnetic flux. About 1% of the flux emerging in the southern hemisphere is transported across the equator, but only 0.1%–0.2% reaches high latitudes to reverse and regenerate a weak polar field in the northern hemisphere. The polarity reversals in the northern hemisphere are delayed compared to the southern hemisphere, leading to a quadrupole Sun lasting for several years.

scholarly journals ASYMMETRY IN APPEARANCE OF THE LEADING AND FOLLOWING POLARITIES IN THE PHOTOSPHERIC MAGNETIC FIELD AT THE EARLY STAGE OF ACTIVE REGION FORMATION

2020 ◽  
Vol 6 (4) ◽  
pp. 3-9
Author(s):  
Victor Grigoryev ◽  
Lyudmila Ermakova ◽  
Anna Khlystova
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Visual Inspection ◽  
Early Stage ◽  
Active Regions ◽  
Longitudinal Component ◽  
Photospheric Magnetic Field ◽  
Line Of Sight ◽  
Flux Dynamics ◽  
The Magnetic Field

We study the evolution of the photospheric magnetic field at the early stage of active region development. We use data on longitudinal component of the magnetic field and line-of-sight velocities from SOHO/MDI and SDO/HMI. The visual inspection of 48 cases of birth of active regions and the detailed analysis of the magnetic flux dynamics in 4 active regions have shown that at the time of emergence of a new magnetic field, the field of the following polarity is the first to be detected in the photosphere. The flux asymmetry of the leading and following polarities persists for several tens of minutes. The observed asymmetry of magnetic fluxes supports the results of the numerical simulation of emergence of the active region magnetic field in the upper layers of the convective zone, which has been carried out by Rempel and Cheung [2014].

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