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Abstract: Long-lived >20 days sunspot groups extracted from the Greenwich Photo-heliographic Results GPR are examined for evidence of decadal change. Theproblem of identifying sunspot groups which are observed on consecutive solarrotations recurrent sunspot groups is tackled by first constructing manuallyan example dataset of recurrent sunspot groups and then using machine learningto generalise this subset to the whole GPR. The resulting dataset of recurrentsunspot groups is verified against previous work by A. Maunder and other RoyalGreenwich Observatory RGO compilers. Recurrent groups are found to exhibit aslightly larger value for the Gnevyshev-Waldmeier Relationship than the valuefound by Petrovay and van Driel-Gesztelyi Solar Phys. 51, 25, 1997, who usedrecurrence data from the Debrecen Photoheliographic Results. Evidence forsunspot group lifetime change over the previous century is observed withinrecurrent groups. A lifetime increase of 1.4 between 1915 and 1940 is found,which closely agrees with results from Blanter et al. Solar Phys. 237, 329,2006. Furthermore, this increase is found to exist over a longer period 1915to 1950 than previously thought and provisional evidence is found for adecline between 1950 and 1965. Possible applications of machine-learningprocedures to the analysis of historical sunspot observations, thedetermination of the magnetic topology of the solar corona and the incidence ofsevere space-weather events are outlined briefly.



Author: R. Henwood, S.C. Chapman, D.M. Willis

Source: https://arxiv.org/



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