Cluster analysis of the space-time distribution of sunspot groups during solar cycle no. 20

Kristóf Petrovay, Bashir K. Abuzeid

Research output: Contribution to journalArticle

7 Citations (Scopus)


Cluster analysis (a Bayesian iteration procedure) was used to study the space-time distribution of sunspot groups in the time interval from 1965 to 1977. (Data were taken from the Greenwich and Debrecen Heliographic Results.) The distribution proved to be significantly non-random for the 8-10 groups cluster-1 (gr cl-1) level of clustering. Convincing evidence also favours non-random behaviour for other levels of clustering from the lowest (3-4 gr cl-1) up to the highest (∼ 150 gr cl-1) level. The rotation rate of the non-random pattern is generally slightly lower than the Carrington rate. The 8-10 gr cl-1 level, crudely corresponding to the 'sunspot nests' investigated earlier, was studied in more detail. The cycle- and latitude-averaged rotational rate of the nests is slightly (∼ 1%) but significantly lower than the Carrington rate. Their differential rotation is strongly reduced: the cycle-averaged rotational rate varies only by 2-3% within the sunspot belt. A slight but significant bimodality is seen in the differential rotation curve: the intermediate latitudes (φ ∼ 10°-20°) show a somewhat slower rotation than both the equatorial and the higher latitude regions. This might be explained by a time-dependence of the rotation rate coupled with the butterfly diagram.

Original languageEnglish
Pages (from-to)231-237
Number of pages7
JournalSolar Physics
Issue number2
Publication statusPublished - Feb 1 1991

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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