Flux emergence within mature 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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