On the relative roles of unipolar and mixed-polarity fields

Abstract

Away from plages, solar magnetic fields may be classified as unipolar or as of mixed polarity, though the distinction is strictly arbitrary. The dividing line used here is 0.4 ≤ ¦B _minor/B _major¦ ≤ 1, where average fields of major and minor polarities are measured over large areas. Some of their statistical properties and cyclical variations are detailed. In unipolar regions, 3 ≲ B _major≲ 50 G, B _minor ≈ 0.1 B _major, and ¦B¦ ≈ 1.1 B _major. In regions of mixed polarity, 3.5 ≲ ¦B¦≲ 10 G.

Below latitudes of ± 60°, mixed polarities predominate for about 5 yr around sunspot minimum. For several years around sunspot maximum, unipolar fields fill the 20°–40° zone completely, and occupy about 75% of the 0°–20° and 40°–60° zones.

The polar unipolar fields are weak on the whole (Bmajor ≈ 4 G for 6 typical days in 1976–79), with small regions having stronger fields at times, probably not exceeding B _major = 10 G. Again B _minor ≈ 0.1 B _major. There is no direct way at present of measuring properties of polar mixed fields, such as may occur around sunspot maximum, but by inference ¦B¦ ≈ 2 to 5 G.