Making Sense of Sunspot Decay. I. Parabolic Decay Law and Gnevyshev-Waldmeier Relation
In a statistical study of the decay of individual sunspots based on DPR data we find that the mean instantaneous area decay rate is related to the spot radius r and the maximal radius r0 as D=C r/r0, C=32.0 +- 0.26 MSH/day. This implies that sunspots on the mean follow a parabolic decay law; the traditional linear decay law is excluded by the data
van Driel-Gesztelyi, L. et al.
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1997