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Solar Cycle Evolution of the General Magnetic Field

  • Hirokazu Yoshimura (a1)

Extract

The data from magnetic field synoptic charts at Mt. Wilson for 16 years are separated into axisymmetric and nonaxisymmetric fields. The axisymmetric field derived simply by averaging over longitude corresponds to the general magnetic field and can be regarded as reflecting the poloidal (radial) field since bipolar magnetic fields which have been regarded as reflecting the toroidal field are cancelled out by the averaging. The evolution of pattern of the latitudinal distribution of this field shows a conspicuous appearance similar to the Butterfly Diagram of sunspots but having two branches of different polarity in each hemisphere. The two branches start from the middle latitudes, and one branch propagates towards the pole and the other toward the equator. This shows that the solar general magnetic field behaves like a quadrupole not a dipole as was previously believed. This feature is exactly what has been predicted by a numerical solar cycle model driven by the dynamo action of the global convection. Another axisymmetric field is also derived by averaging over longitude the absolute value of the magnetic field after subtracting the poloidal field. This field corresponds to the toroidal field since if this field is averaged over longitude it vanishes. The evolutionary pattern of the latitudinal distribution of this field shows a feature quite similar to the Butterfly Diagram of sunspots. These features of the two fields become conspicuous only after averaging over many rotations, e.g., over 27 rotations (2 yr): such a diagram averaged over a small number of rotations shows rather large noise.

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Copyright

References

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Yoshimura, H.: 1975a, Astrophys. J. Suppl. Series 29, 467.
Yoshimura, H.: 1975b, Astrophys. J. 201, 740.
Yoshimura, H.: 1976, Solar Phys. (in press).

Solar Cycle Evolution of the General Magnetic Field

  • Hirokazu Yoshimura (a1)

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