Influence of the Change in the Relative Number of Pores in Activity Cycles on the Reconstruction of the Sunspot Index

Abstract

An analysis of the relative number of groups in cycles 21–24 based on the digitization of observations of sunspots at the Locarno Observatory (Locarno, Switzerland) was performed. In the Zurich classification of sunspot groups, there are classes from A to J. The classes correspond to the process of development and decay of sunspot groups. Class A and B groups correspond to single pores or small pore clusters (class A) and bipolar group (class B). For the reconstruction of solar indices, the relative number of groups (A + B) is of great importance. We found significant variations in the relative number of spot groups (A + B) in the activity cycles. If the relative number of groups (A + B) at the activity minima is 45–50%, then a decrease to 25–30% at the activity cycle maxima is observed. In the original spot index R, proposed by R. Wolf, pores were not considered, and many cores united by one penumbra were counted as one spot. After 1893, at the suggestion of A. Wolfer, the method of calculating the sunspot index changed. The pores and all individual cores in the spots began to be considered – this index is denoted by Rz. It is believed that between the spot indices of the Wolf (R) and Wolfer (Rz), there is a constant transition coefficient close to R/Rz = 0.6. We found that this assumption is incorrect, and R/Rz depends on the amplitude of the activity cycle, varying for the N19 cycle R₁₉~ 0.34, and for the period of the grand minimum R_MM ~ 0.64.