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 \pm 46 ) and B = ( 778 \pm 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 .