Physics
Scientific paper
Sep 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008espm...12.2.68t&link_type=abstract
"12th European Solar Physics Meeting, Freiburg, Germany, held September, 8-12, 2008. Online at http://espm.kis.uni-freiburg.de/,
Physics
Scientific paper
Butterfly diagrams drawn as the prototype created by Maunder are used to constrain dynamo models of the solar cycle, despite the fact they register the mere presence of sunspot groups, disregarding the different physical relevance that groups should be given because of their extension and, accordingly, their magnetic flux. Using sunspot data obtained at INAF -- Osservatorio Astrofisico di Catania in the cycles 20 through 23 (1964-2005), I have obtained a new version of butterfly diagram (BD) in the form of a numerical array, whose elements are the average spotted areas registered for any Carrington rotation at any latitude.
A graphic representation of this array by a set of contour lines connecting equally spotted points will be shown.
The outest contour lines reveal frequent interruptions of the spot zone equatorward drift, and even repeated episodes of poleward drift. Higher and higher-level contour lines are characterized by concave arcs which more and more deeply penetrate the ''butterfly wings'', and eventually split into close lines, embracing small portions of the time-latitude diagram, for time intervals not longer than one or two years.
The BD reveals, therefore, a markedly discrete structure, since the solar activity splits into pulses of activity, involving different photospheric regions at different epochs, throughout the whole cycle. The BD is, therefore, but a cluster of ''knots'' and the ''spot zone'' is the latitude range inside which knots form. Spots are not scattered about one latitude continuously drifting equatorward (as the so-called ''spot average latitude'' is commonly believed to do), but about as many latitudes as the knots are, at as many epochs in the cycle. Each knot is a special population of spots, whose latitude remains unchanged during its short lifetime. Rarely two knots are simultaneously active in the same hemisphere.
The cycle history is but the history of a sequence of knots activations and extinctions.
As a knot forms, the role of the spot zone ''centroid'' passes from a latitude to another one, in a way which could be named a ''latitudinal flip-flop''. That accounts for the alternance of poleward/equatorward drifts of the spot zone, described by the present author for the cycles 20 through 22 (Ternullo; 1997, Solar Phys., 172, 37; 2007, Solar Phys., 240, 153 and 2007, Astron. Nachr., 328, 1023).
Looking for some kind of regularity governing the knots activation throughout the cycle is the new challenge this work presents to the attention of the scientific comunity.
Some hints for a connection with the oscillation detected in the tachocline rotation rate by Howe et al. (2001, IAU Symposium, 203, 41) are suggested.
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