Degree of electric current neutralization and the activity in solar active regions

Abstract Using time-sequence vector magnetic field observation from Helioseismic and Magnetic Imager, we examined the connection of non-neutralized currents and the observed activity in 20 solar active regions (ARs). The net current in a given magnetic polarity is algebraic sum of direct current (DC) and return current (RC) and the ratio |DC/RC| is a measure of degree of net current neutralization (NCN). In the emerging ARs, the non-neutrality of these currents builds with the onset of flux emergence, following the relaxation to neutrality during the separation motion of bipolar regions. Accordingly, some emerging ARs are source regions of CMEs occurring at the time of higher level non-neutrality. ARs in the post-emergence phase can be CME productive provided they have interacting bipolar regions with converging and shearing motions. In these cases, the net current evolves with higher level (>1.3) of non-neutrality. Differently, the |DC/RC| in flaring and quiet ARs vary near unity. In all the AR samples, the |DC/RC| is higher for chiral current density than that for vertical current density. Owing to the fact that the non-neutralized currents arise in the vicinity of sheared polarity-inversion-lines (SPILs), the profiles of the total length of SPIL segments and the degree of NCN follow each other with a positive correlation. We find that the SPIL is localized as small segments in flaring-ARs, whereas it is long continuous in CME-producing ARs. These observations demonstrate the dividing line between the CMEs and flares with the difference being in global or local nature of magnetic shear in the AR that reflected in non-neutralized currents.

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Difference of source regions between fast and slow coronal mass ejections

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2019.13 ◽

2019 ◽

Vol 36 ◽

Cited By ~ 2

Author(s):

B. Filippov

Keyword(s):

Magnetic Field ◽

Coronal Mass Ejections ◽

Solar Flares ◽

Magnetic Energy ◽

Active Regions ◽

Coronal Magnetic Field ◽

Source Regions ◽

Free Magnetic Energy ◽

The Difference ◽

Sunspot Groups

Abstract Coronal mass ejections (CMEs) are tightly related to filament eruptions and usually are their continuation in the upper solar corona. It is common practice to divide all observed CMEs into fast and slow ones. Fast CMEs usually follow eruptive events in active regions near big sunspot groups and associated with major solar flares. Slow CMEs are more related to eruptions of quiescent prominences located far from active regions. We analyse 10 eruptive events with particular attention to the events on 2013 September 29 and on 2016 January 26, one of which was associated with a fast CME, while another was followed by a slow CME. We estimated the initial store of free magnetic energy in the two regions and show the resemblance of pre-eruptive situations. The difference of late behaviour of the two eruptive prominences is a consequence of the different structure of magnetic field above the filaments. We estimated this structure on the basis of potential magnetic field calculations. Analysis of other eight events confirmed that all fast CMEs originate in regions with rapidly changing with height value and direction of coronal magnetic field.

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Electric current density calculation and error analysis of solar active regions

New Astronomy ◽

10.1016/j.newast.2008.09.002 ◽

2009 ◽

Vol 14 (3) ◽

pp. 294-301 ◽

Cited By ~ 1

Author(s):

H.F. Liang ◽

L. Ma ◽

H.J. Zhao ◽

F.Y. Xiang

Keyword(s):

Error Analysis ◽

Electric Current ◽

Current Density ◽

Active Regions ◽

Electric Current Density ◽

Density Calculation ◽

Solar Active Regions

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The source and engine of coronal mass ejections

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2018.0094 ◽

2019 ◽

Vol 377 (2148) ◽

pp. 20180094 ◽

Cited By ~ 13

Author(s):

Manolis K. Georgoulis ◽

Alexander Nindos ◽

Hongqi Zhang

Keyword(s):

Space Weather ◽

Coronal Mass Ejections ◽

Large Scale ◽

Magnetic Energy ◽

Active Regions ◽

Magnetic Polarity ◽

X Rays ◽

Polarity Inversion ◽

Magnetic Flux Ropes ◽

Causal Sequence

Coronal mass ejections (CMEs) are large-scale expulsions of coronal plasma and magnetic field propagating through the heliosphere. Because CMEs are observed by white-light coronagraphs which, by design, occult the solar disc, supporting disc observations (e.g. in EUV, soft X-rays, Halpha and radio) must be employed for the study of their source regions and early development phases. We review the key properties of CME sources and highlight a certain causal sequence of effects that may occur whenever a strong (flux-massive and sheared) magnetic polarity inversion line develops in the coronal base of eruptive active regions (ARs). Storing non-potential magnetic energy and helicity in a much more efficient way than ARs lacking strong polarity inversion lines, eruptive regions engage in an irreversible course, making eruptions inevitable and triggered when certain thresholds of free energy and helicity are crossed. This evolution favours the formation of pre-eruption magnetic flux ropes. We describe the steps of this plausible path to sketch a picture of the pre-eruptive phase of CMEs that may apply to most events, particularly the ones populating the high end of the energy/helicity distribution, that also tend to have the strongest space-weather implications. This article is part of the theme issue ‘Solar eruptions and their space weather impact’.

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The Source Locations of Major Flares and CMEs in the Emerging Active Regions

10.5194/egusphere-egu21-31 ◽

2021 ◽

Author(s):

Lijuan Liu ◽

Yuming Wang ◽

Zhenjuan Zhou ◽

Jun Cui

Keyword(s):

Coronal Mass Ejections ◽

Active Regions ◽

The Self ◽

Flux Emergence ◽

Polarity Inversion ◽

Common Process ◽

Solar Active Regions

<p>Major flares and coronal mass ejections (CMEs) tend to originate from the compact&#160;polarity inversion lines (PILs) in the solar active regions (ARs). Recently, a scenario named as &#8220;collisional shearing&#8221; is proposed by Chintzoglou et al. (2019) to explain the&#160;phenomenon, which suggests that the collision between different emerging bipoles is able&#160;to form the compact PIL, driving the shearing and flux cancellation that are responsible to the subsequent large activities. In this work, through tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs,&#160;we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of &#8220;collisional shearing&#8221;. We find that none of the active PILs is the self PIL&#160;(sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional&#160;PILs (cPILs) formed due to the collision between different bipoles, 6 from the conjoined&#160;systems of sPIL and cPIL, and 2 from the conjoined systems of sPIL and ePIL (external&#160;&#160;PIL between the AR and the nearby preexisting polarities). Collision accompanied by&#160;shearing and flux cancellation is found developing at all PILs prior to the eruptions,&#160;with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we&#160;find that the magnitude of the flares is positively correlated with the collisional length&#160;of the active PILs, indicating that the intenser activities tend to originate from the&#160;PILs with severer collision. The results suggest that the &#8220;collisional shearing&#8221;, i.e.,&#160;bipole-bipole interaction during the flux emergence is a common process in driving the&#160;major activities in emerging ARs.</p>

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Radio Measurements of Coronal Magnetic Fields

International Astronomical Union Colloquium ◽

10.1017/s0252921100024933 ◽

1994 ◽

Vol 144 ◽

pp. 21-28 ◽

Cited By ~ 4

Author(s):

G. B. Gelfreikh

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Solar Corona ◽

Active Regions ◽

High Sensitivity ◽

Coronal Magnetic Field ◽

Transverse Magnetic ◽

Radio Sources ◽

Radio Waves ◽

Solar Active Regions

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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