Figure 2: Magnetic variability over the last three decades.

Comparison of the variation in (monthly) sunspot number (SSN) and flare record with the ‘butterfly’ diagram of the photospheric magnetic field over the past three solar cycles. (a) Total (black) and hemispheric (red—north; blue—south) monthly sunspot numbers (hSSN) from the Solar influences data center (SIDC). (b) Variation of the hemispheric daily rate of flares larger than ‘B’ magnitude in the GOES (red—north; blue—south) and RHESSI (orange—north; purple—south) records. Note the strong modulation in the flare rate, the hemispheric differences in flare rates and that flare maximum does not occur at the same time as sunspot maximum—over the record shown, the flare activity maximum occurs several years post sunspot maximum. (c) Latitude–time distribution of the GOES flares of b. (d) Latitude–time variation of the photospheric magnetic field at the central meridian. Note the strong correspondence between the poleward pulses of photospheric magnetism and the surges in flare activity from c and b. All panels show a thick vertical dashed line indicating the time of sunspot maximum and the lower two panels show dot-dashed lines at 55° to delineate high- and low-latitude variation.