Surface appearance of dynamo-generated large-scale fields
by
MrJörn Warnecke(Nordita)
→
Europe/Stockholm
122:026 (House 12)
122:026 (House 12)
Description
Twisted magnetic fields are frequently seen to emerge above the visible surface of the Sun. This emergence is usually associated with the rise of buoyant magnetic flux structures. Here we address the question about magnetic field structures that are generated by a turbulent large-scale dynamo just beneath the surface. The computational domain is split into two parts. In the lower part, which we refer to as the turbulence zone, the flow is driven by an adopted helical forcing function leading to dynamo action. Above this region, which we refer to as the exterior, a nearly force-free magnetic field is computed at each time step using the stress-and-relax method. A twisted arcade-like field structure is found to emerge in the exterior above the turbulence zone. Strong current sheets tend to be formed above the neutral line, where the vertical field component vanishes. The degree to which the exterior field is force-free is estimated as the ratio of the dot product of current density and field strength to their respective rms values. This ratio reaches values of up to 95% in the exterior. A weak outward wind is driven by the residual Lorentz force.
