Toroidal field at the base of the convection zone (r = 0.7  R_⊙). The upper panel shows the evolution as a function of latitude and time. In the lower panel the average unsigned toroidal flux between ± 45° latitude corresponding to odd and even cycles is shown using dashed and solid curves, respectively. The correlation coefficient between the maxima of the toroidal field at the base of the convection zone and the maxima of the observed sunspot number for cycles 15−21 is 0.93.