The Relationship between Magnetic Gradient and Magnetic Shear in Five Super Active Regions Producing Great Flares

Wang, Haimin; Song, Hongjia; Jing, Ju; Yurchyshyn, Vasyl; Deng, Ying; Zhang, Hong Qi; Falconer, D. A.; Li, Jing

doi:10.1088/1009-9271/6/4/11

Cited by 32 publications

(25 citation statements)

References 23 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Prasad (2000) used the similar parameter of the magnetic gradient to characterize the stressed magnetic fields in active regions. Wang et al (2006) found a close correlation between magnetic shear and magnetic gradient; both can be used as a good proxy to predict flares. This was further demonstrated by statistical studies Jing et al 2006).…”

Section: Introductionmentioning

confidence: 76%

Rapid Changes of Photospheric Magnetic Fields around Flaring Magnetic Neutral Lines

Wang

2006

ApJ

View full text Add to dashboard Cite

In this paper we study the short-term evolution of magnetic fields associated with five flares in -sunspots. We concentrate on the analysis of the magnetic gradient along the flaring neutral lines (NLs). Obvious changes of the magnetic gradient occurred immediately and rapidly following the onset of each flare. A rapid gradient increase was found to be associated with three events, while a decrease was associated with the other two. The changes were permanent, and therefore not likely due to the flare emissions. In addition, we evaluated the mean relative motions between the two magnetic polarities in these -regions, in the directions parallel and perpendicular to the flaring NLs. We derived the mean positions of the two magnetic polarities using a center-of-mass (CoM) calculation and found that (1) converging motions correspond to a gradient increase and diverging motions, to a decrease; (2) for all the events, there appeared a sudden release of magnetic shear associated with each flare, signified by a decrease of CoM separation between 500 and 1200 km in the direction parallel to the NLs. Combining the findings presented here with those in previous papers, we propose that these results are evidence of magnetic reconnection at or close to the photosphere. When an active region is away from the solar disk center, the reconnected transverse fields cause an apparent increase of the flux in the polarity toward the limb and a decrease for the polarity closer to the disk center. This observational pattern was indeed found for all 10 available events that have been studied in the literature and in this paper. Finally, we offer some predictions for future observations when high-quality vector magnetogram sequences become available.

show abstract

Section: Introductionmentioning

confidence: 76%

Rapid Changes of Photospheric Magnetic Fields around Flaring Magnetic Neutral Lines

Wang

2006

ApJ

View full text Add to dashboard Cite

show abstract

“…To characterize the nonpotentiality of the active region, we calculate magnetic shearS, defined as the product of field strength and shear angle 37,38 :S = |B| · θ ,…”

Section: Methodsmentioning

confidence: 99%

High-resolution observations of flare precursors in the low solar atmosphere

et al. 2017

Self Cite

View full text Add to dashboard Cite

Solar flares are generally believed to be powered by free magnetic energy stored in the corona 1 , but the build up of coronal energy alone may be insufficient for the imminent flare occurrence 2 . The flare onset mechanism is a critical but less understood problem, insights into which could be gained from small-scale energy releases known as precursors, which are observed as small pre-flare brightenings in various wavelengths (e.g., refs 3-13 ), and also from certain small-scale magnetic configurations such as the opposite polarity fluxes [14][15][16] , where magnetic orientation of small bipoles is opposite to that of the ambient main polarities. However, high-resolution observations of flare precursors together with the associated photospheric magnetic field dynamics are lacking. Here we study precursors of a flare using unprecedented spatiotemporal resolution of the 1.6 m New Solar Telescope, complemented by novel microwave data. Two episodes of precursor brightenings are initiated at a small-scale magnetic channel 17-20 (a form of opposite polarity fluxes) with multiple polarity inversions and enhanced magnetic fluxes and currents, lying near the footpoints of sheared magnetic loops. The low-atmospheric origin of these precursor emissions is corroborated by microwave spectra. We propose that the emerging magnetic channel field interacts with the sheared arcades to cause precursor brightenings at the main flare core region. These high-resolution results provide evidence of low-atmospheric small-scale energy release and possible relationship to the onset of the main flare.We study the 22 June 2015 M6.5 flare (SOL2015-06-22T18:23) using Hα (line-center and red-wing) images and photospheric vector magnetograms obtained by the recently commissioned 1.6 m New Solar Telescope (NST) 21, 22 at Big Bear Solar Observatory (BBSO), which is stabilized by a high-order adaptive optics (AO) system (see Methods). In particular, the vector field data is taken by the Near InfraRed Imaging Spectropolarimeter (NIRIS) 23 at the 1.56µ Fe I line. These observations have the highest spatial resolution ever achieved for the solar observations (∼70 km for Hα and ∼170 km for vector field) and rapid cadence (28 s for Hα and 87 s for vector field). Also used are flare microwave spectra and time profiles from the new Expanded Owens Valley Solar Array (EOVSA; see Methods), and time profiles of hard X-ray (HXR) and soft X-ray (SXR) fluxes from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) 24 and the Geostationary Operational Environmental Satellite (GOES)-15, respectively. Ancillary data of full-disk corona images and magnetograms from the Solar Dynamics Observatory (SDO) 25 are additionally used. The long-duration 22 June 2015 M6.5 flare occurred near the disk center (8• W, 12• N) at NOAA active region (AR) 12371. Time profiles of flare emissions in different wavelengths (including HXR, SXR, and microwave) clearly display that soon before the flare impulsive phase starting from ∼17:51 UT, there are two short ep...

show abstract

“…The nonpotentiality can be evaluated using magnetic shearS, which is computed here as the product of field strength and shear angle (Wang et al 1994(Wang et al , 2006Jing et al 2008):…”

Section: Change Of Cmf Topology Inferred From Nlfff Modelmentioning

confidence: 99%

Rapid Changes of Photospheric Magnetic Field After Tether-Cutting Reconnection and Magnetic Implosion

Liu

Deng

et al. 2011

ApJ

Self Cite

View full text Add to dashboard Cite

The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. This Letter reports such a rapid change of magnetic fields during the 2011 February 13 M6.6 flare in NOAA AR 11158 that we found from the vector magnetograms of the Helioseismic and Magnetic Imager (HMI) with 12 minute cadence. High-resolution magnetograms of Hinode that are available at ∼−5.5, −1.5, 1.5, and 4 hr relative to the flare maximum are used to reconstruct a three-dimensional coronal magnetic field under the nonlinear force-free field (NLFFF) assumption. UV and hard X-ray images are also used to illuminate the magnetic field evolution and energy release. The rapid change is mainly detected by HMI in a compact region lying in the center of the magnetic sigmoid, where the mean horizontal field strength exhibited a significant increase of 28%. The region lies between the initial strong UV and hard X-ray sources in the chromosphere, which are cospatial with the central feet of the sigmoid according to the NLFFF model. The NLFFF model further shows that strong coronal currents are concentrated immediately above the region, and that, more intriguingly, the coronal current system underwent an apparent downward collapse after the sigmoid eruption. These results are discussed in favor of both the tether-cutting reconnection producing the flare and the ensuing implosion of the coronal field resulting from the energy release.

show abstract

The Relationship between Magnetic Gradient and Magnetic Shear in Five Super Active Regions Producing Great Flares

Cited by 32 publications

References 23 publications

Rapid Changes of Photospheric Magnetic Fields around Flaring Magnetic Neutral Lines

Rapid Changes of Photospheric Magnetic Fields around Flaring Magnetic Neutral Lines

High-resolution observations of flare precursors in the low solar atmosphere

Rapid Changes of Photospheric Magnetic Field After Tether-Cutting Reconnection and Magnetic Implosion

Contact Info

Product

Resources

About