Transport of Magnetic Fields on the Sun.

Abstract

The dispersal and migration of unipolar and bipolar magnetic regions on the Sun are quantitatively interpreted as a random-walk, diffusion-like process caused by supergranulation convection currents in the Sun's outer layers The time-dependent strength and sign of the polar fields are deduced approximately from the positions, fluxes, and axial tilts of the individual spot groups associated with the sunspot cycle. The well-known predominance of the preceding spot of a group is attributed to a characteristic field configuration which renders p spots relatively stable against fragmentation by the supergranulation currents The relation of the random-walk process to the solar cycle is briefly discussed, and the 11-year period is interpreted as the summation of five more-or-less distinct parts A major advance in our understanding of the nature of sunspots and of the 22-year solar cycle was made by H. W. Babcock (1961) in his presentation of a theory of the topology of the Sun's subsurface magnetic field-its deformation and amplification by the differential rotation and its eventual systematic eruption through the solar surface to form bipolar sunspot groups. Babcock's theory accounts quite satisfactorily for Sporer's law and Maunder's "butterfly" diagram, Hale's laws of polarity, and the number of sunspots in a cycle. However, some important aspects of the problem cannot yet be said to be well understood. It is the purpose of this paper to further clarify one important aspect of the solar cycle-the expansion and apparent "migration" of unipolar (UM) and bipolar (BM) magnetic regions. We shall present a definite physical mechanism for this phenomenon, and shall use it to account for the neutralization and subsequent reversal of the polar field. The mechanism may further provide an explanation for the relative predominance and longevity of the leading spot of a sunspot group. The means by which field lines may be "prepared" for the next cycle will also be considered.