Statistical characteristics of large sunspots in solar activity cycles 17–23

Abstract

Integral and differential distributions of sunspot diameters are studied for the last seven 11-year cycles of solar activity. Data of the Greenwich catalogue, Pulkovo’s database, and the “Solniechnyie Dannyie” bulletin are used. We found that the average index of integral distribution α is 6.0 for the diameters from 50 to 90 Mm and independent of the Wolf’s numbers, but it depends on a cycle phase in the majority of cycles (four of seven), i.e., it is higher during the ascending phase, of intermediate value during the maximum phase and minimum during the declining phase. Cycles 17, 18, and 22 behave differently: the index α is either invariable with phase or the variations differ from the above ones. It turned out that cycles 17 and 18 are peculiar by sunspot diameters, i.e., sunspots of up to 140–180 Mm in diameter, the largest over the last 80 years, have been observed. Three assumptions concerning the nature of these gigantic sunspots have been proposed: (a) these sunspots occur due to changes in differential rotation of the sun, (b) these sunspots are a certain independent statistical assembly formed in a sporadic discrete region of the convective zone, and (c) these sunspots are surface “fragments” of the relict magnetic field of the solar nucleus.