Long-term variations in sunspot magnetic field - area relation

TL;DR

This study analyzes long-term changes in the relationship between sunspot magnetic field strength and area over two solar cycles, revealing cycle-dependent variations and evidence of centennial-scale changes in sunspot properties.

Contribution

It provides new insights into how the H-S relation varies with solar cycle phase and identifies long-term variations in sunspot populations and properties.

Findings

Correlation between H and S varies with solar cycle phase.

The A coefficient decreases significantly after 2001.

Two distinct sunspot populations with different properties exist.

Abstract

Using observations of sunspot magnetic field strengths (H) from the Crimean Astrophysical Observatory (CrAO) and area (S) of sunspots from the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory, we investigate the changes in the relation between H and S over the period of about two solar cycles (1994-2013). The data were fitted by H = A + B log S, where A = (778+/-46) and B = (778+/-25). We show that the correlation between H and S varies with the phase of solar cycle, and $A$ coefficient decreases significantly after year 2001, while B coefficient does not change significantly. Furthermore, our data confirm the presence of two distinct populations in distribution of sunspots (small sunspots with weaker field strength and large sunspots with stronger field). We show that relative contribution of each component to the distribution of sunspots by their area changes with the phase of solar cycle and on longer-then-cycle periods. We interpret these changes as a signature of a long-term (centennial) variations in properties of sunspots.