Making sense of sunspot decay I. Parabolic Decay Law and Gnevyshev-Waldmeier Relation

K. Petrovay, L. Van Driel-Gesztelyi

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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 ro and the maximum radius ro as D = CDr/r0, CD = 32.0 ± 0.26 MSH day-1. This implies that sunspots on the mean follow a parabolic decay law; the traditional linear decay law is excluded by the data. The validity of the Gnevyshev-Waldmeier relationship between the maximum area A0 and lifetime T of a spot group, A0/T ≃ 10 MSH day-1, is also demonstrated for individual sunspots. No evidence is found for a supposed supergranular 'quantization' of sunspot areas. Our results strongly support the recent turbulent erosion model of sunspot decay while all other models are excluded.

Original languageEnglish
Pages (from-to)249-266
Number of pages18
JournalSolar Physics
Issue number2
Publication statusPublished - Jan 1 1997


ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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