On the relative roles of unipolar and mixed-polarity fields |
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Authors: | Ronald G Giovanelli |
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Institution: | (1) Kitt Peak National Observatory, P.O. Box 26732, 85726 Tucson, Ariz., U.S.A.;(2) Present address: CSIRO Division of Applied Physics, P.O. Box 218, 2070 Lindfield, NSW, Australia |
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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.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. |
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