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Paper: The relation between Magnetic Energy and Helicity and their accumulation in Eruptive Solar Active Regions
Volume: 470, 370 Years of Astronomy in Utrecht
Page: 59
Authors: Tziotziou, K.; Georgoulis, M. K.; Raouafi, N.-E.
Abstract: Magnetic free energy and relative magnetic helicity are two important quantities characterizing solar active regions (ARs). Although the importance of free magnetic energy storage for solar eruptions is widely accepted, the role of magnetic helicity, that quantifies the stress and distortion of the magnetic field compared to its lowest (potential) energy state, is still under debate. A new nonlinear force-free method designed to calculate the instantaneous free magnetic energy and relative magnetic helicity budgets of a solar active region from a single vector magnetogram is presented. A sample of 40 vector magnetograms corresponding to different eruptive and non-eruptive ARs is used to calculate their free magnetic energy and relative magnetic helicity budgets, aiming to find a statistically robust correlation between them. The derived correlation implies that magnetic helicity, besides free magnetic energy, is a crucial ingredient for active regions hosting major (M-class and higher) solar eruptions. Eruptive active regions appear well segregated from non-eruptive ones in both free energy and relative helicity with eruptive major flares occurring in ARs with free energy and helicity exceeding 4×1031 erg and 2×1042 Mx2, respectively. Helicity is expelled from ARs mainly in the form of coronal mass ejections (CMEs) and the above helicity threshold agrees well with estimates of typical helicity contents of CMEs.
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