Fig. 4

Constraints on the solar magnetic cycle based on observations over the past century. The top panel depicts the quasi-periodic variation of sunspot numbers, the middle panel depicts the variation of the polar field in the northern and southern hemispheres gleaned from polar faculae counts (Muñoz-Jaramillo et al. 2013) and polar field observations and the bottom panel depicts the sunspot butterfly diagram, i.e., the spatio-temporal evolution of latitudes where sunspots appear. Theoretical dynamo models aspire to reproduce these observational constraints, while solar cycle prediction efforts focus on forecasting the strength of future solar cycles(s)