Current helicity constraints in solar dynamo models

Abstract

Abstract.We investigate to what extent the current helicity distribution observed in solar active regions is compatible with solar dynamo models. We use an advanced 2D mean-field dynamo model with dynamo action largely concentrated near the bottom of the convective zone, and 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 obtain butterfly diagrams for both the small-scale current helicity and the large-scale magnetic helicity, and compare 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 −A · 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 B and A are respectively the dynamo generated mean magnetic field and its vector potential.

Magnetic helicity in non-axisymmetric mean-field dynamo

“…Due to this fact the dynamo model demonstrate inversions of the hemispheric helicity rule. This is supported from observations [14,15] and axisymmetric dynamo models [11,16]. It is interesting that the nonaxisymmetric helicity density distribution tends to follow to patterns of the largescale non-axisymmetric magnetic field during evolution.…”