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The crucial role of surface magnetic fields for the solar dynamo

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Science  20 Mar 2015:
Vol. 347, Issue 6228, pp. 1333-1335
DOI: 10.1126/science.1261470

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Sunspot cycle driven by linked fields

Sunspots indicate magnetic flux emerging at the Sun's surface. Sunspots change over an 11-year time scale, which depends on the behavior of the probable magnetic dynamo within. Cameron et al. suggest that the flux revealed by sunspot activity is effectively driven by the magnetic field strength at the Sun's poles. Their mathematical reasoning explains why the polar field activity can predict the sunspot cycle.

Science, this issue p. 1333

Abstract

Sunspots and the plethora of other phenomena occurring in the course of the 11-year cycle of solar activity are a consequence of the emergence of magnetic flux at the solar surface. The observed orientations of bipolar sunspot groups imply that they originate from toroidal (azimuthally orientated) magnetic flux in the convective envelope of the Sun. We show that the net toroidal magnetic flux generated by differential rotation within a hemisphere of the convection zone is determined by the emerged magnetic flux at the solar surface and thus can be calculated from the observed magnetic field distribution. The main source of the toroidal flux is the roughly dipolar surface magnetic field at the polar caps, which peaks around the minima of the activity cycle.

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