Fig. 1

Ratio of toroidal to poloidal power as a function of spherical harmonic degree. The blue and red spectra represent the ratios of the plate model from PB2002 (Bird 2003) and NNR-MORVEL (Argus et al. 2011), respectively. The upper horizontal axis shows the scale of motion corresponding to the spherical harmonic degree. There are four logarithmic trendlines to fit the data of PB2002: the broken black line is the quadratic fitting curve for the whole spectrum, the yellow line is the linear fitting line for the range from 100 to 1000 km in the scale of motion, and the gray dotted and solid lines represent linear fitting lines for \(l < 20\) (\({>}1000\) km) and \(l > 20\) (\({<}1000\) km), respectively. The range for the yellow line (100–1000 km) is important for the analysis of individual spin motion and the dynamics (Figs. 5, 6). The ratio of total toroidal power to total poloidal power, \(\gamma \), is 0.752 for PB2002