Large-Scale Distribution of Solar Magnetic Fields.

Abstract

Solar magnetograms covering a period of years were used to study the distribution of weak magnetic fields on the solar surface. The semiregular pattern of these background fields is the result of the expansion, weakening, and stretching by differential rotation of magnetic fields of old active regions and their interaction with neighboring fields, and of the continuing development of magnetic fields of new regions within the pattern. The net result is a slowly changing pattern of background fields which occupies at times during the solar cycle more than 50 per cent of the surface area of the Sun, as seen with the 23" resolution of the magnetograph. The interaction of nearby magnetic fields takes the form of the apparent attraction of features of the same polarity and the apparent repulsion of features of opposite polarity. Sometimes weak magnetic features covering a large area apparently disappear over a period of a few rotations. It is not clear from the observations what the mechanism of this disappearance could be. It is clear from the period near minimum that active regions are concentrated in complexes of activity whose location and development are clearly defined. The largest of these complexes, consisting of many active regions, result in the formation of Unipolar Magnetic Regions (UMR). The polar fields are discussed from the standpoint of the poleward drift of the UMR's.