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

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

Feb 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991soph..131..231p&link_type=abstract

Solar Physics (ISSN 0038-0938), vol. 131, Feb. 1991, p. 231-237.

Physics

6

Cluster Analysis, Solar Cycles, Solar Rotation, Space-Time Functions, Sunspot Cycle, Solar Activity Effects, Solar Flares, Time Dependence

Scientific paper

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, using data from the Greenwich and Debrecen Heliographic Results. The distribution proved to be significantly nonrandom for the 8-10 groups/cluster (gr/cl) level of clustering. Convincing evidence also favors nonrandom behavior for other levels of clustering from the lowest (3-4 gr/cl) up to the highest (about 150 gr/cl) level. The rotation rate of the nonrandom pattern is generally slightly lower than the Carrington rate. The 8-10 gr/cl 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 (about 1 percent) but significantly lower than the Carrington rate. Their differential rotation is strongly reduced: the cycle-averaged rotational rate varies only by 2-3 percent within the sunspot belt. A slight but significant bimodality is seen in the differential rotation curve: the intermediate latitudes (phi about 10 - 20 deg) 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.

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