Speaker
Description
Sunspot observations made by Rudolf Wolf (1816 - 1893) during the years from 1849 to 1893 form the core of the Wolf series of sunspot number index, the longest directly observed series of solar activity. Homogeneity is considered as the most important property of the Wolf series, since without a stable scale no valid conclusions about variations in the long term progress of solar activity can be drawn. From 1849 to 1861 the scale of the Wolf series was defined by the observations Rudolf Wolf made with his 83/1320 mm Fraunhofer refractor (Friedli, 2016). For the later years Wolf transferred this scale to the 40/700 mm Parisian Refractor, backwards in time the scale was transferred to the observations of Heinrich Schwabe. Both scale transfers were based on a rather limited number of comparison observations including secondary observers. Based on the reconstructed observations of Heinrich Schwabe by Senthamizh Pavai (2015) we reanalyse both scale transfers revealing that the Wolf numbers of Heinrich Schabe should be lowered by a factor of 0.8 relative to the Wolf numbers provided by WDC_SILSO version 1.0. The scale transfer from the 83/1320 mm Fraunhoferrefractor to the 40/700 mm Parisian refractor contains a hitherto unnown intercept leading to time-dependend scale variations if unconsidered. Thus, we compare the recalibrated original observations from Wolf with the observations made by Heinrich Leppig, Heinrich Weber and Alfred Wolfer and establish a corrected scale transfer to the recalculated Wolf series in 1877 as presented in Friedli (2020).
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