Speaker
Description
Observations of photospheric magnetic fields, active region emergence, and surface flows provide the primary constraints on predicting solar cycle variability. In particular, the strength of the polar fields during solar minimum remains a robust indicator of the amplitude of the subsequent cycle. However, reliable polar field measurements are only available for a few decades and key aspects of the solar cycle, such as hemispheric asymmetry, have only recently been examined in detail.
Ca II K observations and long-term sunspot records provide measures of the Sun’s magnetic field evolution prior to routine magnetograph measurements. Modern calibration methods and statistical approaches allow us to reconstruct aspects of the Sun’s large-scale magnetic field over multiple centuries. Variations in active region emergence patterns (such as timing and tilt) introduce uncertainty that fundamentally limit predictive capabilities. Differences in northern and southern hemispheric activity levels and reversal timings can lead to cross-equatorial flux transport and hemispheric coupling, with implications for the global heliospheric field.
In this talk, I will review what we have learned from observations of photospheric magnetism and how combining modern magnetograph observations with careful analysis of historical records spanning centuries continues to refine our understanding of solar cycle evolution and cycle-to-cycle variability. This provides indirect constraints on the Sun’s polar fields, offers valuable insight into secular variability, placing recent cycles in a longer-term context, and improves our ability to quantify sources of solar cycle variability. This is a critical next step to making more accurate predictions for the next cycle, as well as long-term changes in the heliospheric and space climate environment.