A solar dynamo in the overshoot layer: cycle period and butterfly diagram.

Details A solar dynamo in the overshoot layer: cycle period and butterfly diagram. A solar dynamo in the overshoot layer: cycle period and butterfly diagram.

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...296..557r&link_type=abstract

Astronomy and Astrophysics, v.296, p.557

Astronomy and Astrophysics

Astrophysics

108

Magnetohydrodynamics, Turbulence, Sun: Magnetic Fields, Stars: Magnetic Fields

Scientific paper

We construct a solar dynamo model for the overshoot layer where a strong gradient in the turbulence velocity is assumed to produce the α-effect. A recent rotation law from helioseismology is adopted and meridional flows are ignored. Since in the overshoot layer the convective turnover time is long compared with the rotation period, the full structure of the alpha and turbulent diffusion tensors appearing in the expressions for the turbulent electromotive force (EMF) must be retained in the computations. The important toroidal component of α is negative in the overshoot layer. In this layer the turbulence is considered as rarefied with a "dilution factor" ɛ<1 to account for the reduced EMF due to the intermittent nature of the magnetism. The cycle period increases with decreasing ɛ, and for ɛ=~0.2-0.5 the 22yr solar cycle period is reproduced, depending on details of the model. The effect of magnetic buoyancy can increase the cycle period further. If this layer is thinner than =~30Mm, the number of toroidal field belts is too large compared to the sun. Due to the strong rotational influence on the turbulence in the presence of a sharp change of the turbulence intensity at the bottom of the convection zone, the α-effect is more concentrated to the equatorial region. This leads to more realistic butterfly diagrams. Observations indicate, however, that radial and azimuthal field components are out of phase, which is not reproduced by our model.

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