H. Zhang, D. Moss, N. Kleeorin, K. Kuzanyan, I. Rogachevskii, D. Sokoloff, Y. Gao, H. Xu
We demonstrate that the current helicity observed in solar active regions
traces the magnetic helicity of the large-scale dynamo generated field. We use
an advanced 2D mean-field dynamo model with dynamo saturation based on the
evolution of the magnetic helicity and algebraic quenching. For comparison, we
also studied a more basic 2D mean-field dynamo model with simple algebraic
alpha quenching only. Using these numerical models we obtained butterfly
diagrams both for the small-scale current helicity and also for the large-scale
magnetic helicity, and compared them with the butterfly diagram for the current
helicity in active regions obtained from observations. This comparison shows
that the current helicity of active regions, as estimated by $-{\bf A} \cdot
{\bf B}$ evaluated at the depth from which the active region arises, resembles
the observational data much better than the small-scale current helicity
calculated directly from the helicity evolution equation. Here ${\bf B}$ and
${\bf A}$ are respectively the dynamo generated mean magnetic field and its
vector potential. A theoretical interpretation of these results is given.
View original:
http://arxiv.org/abs/1110.4387
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