Sule, G. The origin of the magnetic field of the Sun is one of the key questions in solar astrophysics.
A large-scale circulation may transport magnetic fields below the convection zone and store them there. The tachocline is the thin transition between uniform rotation in the interior and the differential rotation in the upper convection zone.
If the magnetic fields are stored and amplified in the tachocline, they must be stable. The stability of the magnetic tachocline will tell us whether the storage of magentic fields below the convection zone is one part of the dynamo process. If the tachocline becomes unstable for strong fields necessary to produce sunspots, the dynamo must reside closer to the surface of the sun.
We investigate the stability of two belts of so-called toroidal magnetic fields red lines in Figure 1. Numerical computations cannot directly reproduce solar conditions, but our present calculations lead to maximum magnetic fields of about Gauss. Stronger fields cannot be stored below the convection zone.
Faster computers will tell the exact limit in future computations. A related problem is the interaction between the convection zone and the solar core. The differential rotation in the convection zone continuously generates a large-scale circulation which is directed to the pole at the solar surface, and towards the equator at the bottom of the convection zone. We show in a new model that the penetration of the circulation into the solar core is very small.
The penetration depth depends on whether or not the tachocline is turbulent. The transport of magnetic fields into the tachocline must be weak, too. Figure 1: Magnetic field belts are placed below the convection zone in order to study their stability. The belts are indicated by red field lines.
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Figure 2: Penetration depth of the meridional circulation at the transition between convection zone and core, as a function of the turbulence instensity. Personal tools Log in.
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