Cluster analysis of the space-time distribution of sunspot groups during solar cycle no. 20
✍ Scribed by Kristóf Petrovay; Bashir K. Abuzeid
- Publisher
- Springer
- Year
- 1991
- Tongue
- English
- Weight
- 369 KB
- Volume
- 131
- Category
- Article
- ISSN
- 0038-0938
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✦ Synopsis
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-i) 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 (q5 ~ 10~176 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.