Abstract
The electric current exists because of the non-potential magnetic field in solar active regions. We present the evolution of net current in the solar active region NOAA 10930 as the sum of shear current and twist current by using 27 high-resolution vector magnetograms obtained with Hinode/SOT-SP during 9 – 15 December 2006. This active region was highly eruptive and produced a large number of flares ranging from B to X class. We derived local distribution of shear and twist current densities in this active region and studied the evolution of net shear current (NSC) and net twist current (NTC) in the N-polarity and S-polarity regions separately. We found the following: i) The twist current density was dominant in the umbrae. ii) The footpoint of the emerging flux rope showed a dominant twist current. iii) The shear current density and twist current density appeared in alternate bands around the umbrae. iv) On the scale of the active region, NTC was always larger than NSC. v) Both NTC and NSC decreased after the onset of an X3.4 class flare that occurred on 13 December 2006.
Highlights
The non-potential magnetic field manifests as the electric currents in solar active regions (ARs)
The evolution of an electric current system may originate from two possibilities: one is the emergence of a new electric current system from below the photosphere (Leka et al, 1996), and the second is the rearrangement of the magnetic field in the solar photosphere (Zhang, 1995)
Zhang (2010) analyzed individual magnetic fibrils in the solar active region NOAA 10930 on 12 December 2006. He studied magnetic fibril fields and the relationship between the shear and twist components of the electric current around the magnetic inversion line. He found that the individual magnetic fibrils were dominated by the shear component and the large-scale magnetic region was dominated by the twist component of the electric current
Summary
The non-potential magnetic field manifests as the electric currents in solar active regions (ARs). The distribution of the vertical current density in active regions inferred from vector magnetic fields has been investigated by several authors (Moreton and Severny, 1968; Krall et al, 1982; Ding et al, 1987; Lin and Gaizauskas, 1987; Abramenko, Gopasiuk, and Ogir’, 1991; Hofmann and Kalman, 1991; Chen and Zhang, 1992; Wang et al, 1996) All these studies are concerned with the relationship between the distribution of electric currents and solar flares. Zhang (2010) analyzed individual magnetic fibrils in the solar active region NOAA 10930 on 12 December 2006 He studied magnetic fibril fields and the relationship between the shear and twist components of the electric current around the magnetic inversion line. In this paper our objective is to examine the evolution of the net shear current (NSC) and net twist current (NTC) separately in the positive (N) and negative (S) polarity regions in AR 10930 during 9 – 15 December 2006
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