Comparison between the two sunspot number datasets, Wolf sunspot number (WSN) and group sunspot number (GSN), and the respective empirical mode decomposition results for modes j = 1,2. Panels a), b): WSN and GSN data (magenta) and intrinsic mode functions ψ₁ (blue) and ψ₂ (green) for WSN and GSN data. ψ₁ and ψ₂ are offset from the zero value by 350, 600 for WSN and 25, 45 for GSN. Panels c), d): instantaneous frequencies ω₁ (blue) and ω₂ (green) of the j = 1,2 modes for WSN and GSN data. The horizontal black dashed line indicates the 11 yr frequency. Panels d), e): instantaneous amplitudes A₁ (blue) and A₂ (green) of the j = 1,2 modes for WSN and GSN data.