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Evolution of force‐free field parameter in active regions with major eruptive events
Author(s) -
Dumitru Liliana
Publication year - 2021
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.202113801
Subject(s) - physics , northern hemisphere , magnetic field , helicity , torsion (gastropod) , sign (mathematics) , flare , astrophysics , atmospheric sciences , biology , quantum mechanics , zoology , mathematical analysis , mathematics
Using a nonlinear force‐free field (NLFFF) method to extrapolate photospheric magnetic fields, we compute the force‐free field parameter ( α ), which is a measure of torsion of the magnetic field lines. We calculated the α parameter for 62 active regions that produced major eruptive events in solar cycle 24. We verified statistically how the 62 studied active regions obey the hemispheric rule of helicity. In agreement with previous studies, we found that 67% of active regions located in the northern hemisphere have a negative sign for the global alpha parameter α g , and 69% of the active regions situated in the southern hemisphere have a positive sign. We have identified and analyzed five cases of evolution of α g at times when eruptive phenomena occurred in the selected active regions. We find that 52% of cases show an increase of torsion during flares, while only 22% show a decrease. This shows that increasing torsion plays an important role in flare ignition. For the other cases, a definitive conclusion cannot be reached because of multiple variations.