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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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