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Abstract: The sunspots and other solar activity indicators tend to cluster on thesurface of the Sun.These clusters very often occur at certain longitudes thatpersist in time.It is of general interest to find new and simple ways tocharacterize the observed distributions of different indicators and theirbehaviour in time. In the present work we use Greenwich sunspot data toevaluate statistical but not totally coherent stability of sunspot distributionalong latitudes as well as longitudes. The aim was to obtain information on thelongitudinal distribution of the underlying spot-generating mechanism ratherthan on the distribution and migration of sunspots or sunspot groups on thesolar surface. Therefore only sunspot groups were included in the analysis, andonly the time of their first appearance was used. We use simple nonparametricapproach to reveal sunspot migration patterns and their persistency. Ouranalysis shows that regions where spots are generated tend to rotatedifferentially as the spots and spot groups themselves do. The activity areas,however, tend to break down relatively fast, during 7-15 solar rotations. Thisstudy provides a challenge for solar dynamo models, as our results areconsistent with the presence of a non-axisymmetric spot-generating mechanismexperiencing differential rotation known as phase mixing in dynamo theory.The new nonparametric method introduced here, completely independent of thechoice of the longitudinal distribution of sunspots, was found to be a verypowerful tool for spatio-temporal analysis of surface features.

Autor: J. Pelt, M.J. Korpi, I. Tuominen



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