Comparison of the semi-annual variations in various geomagnetic indices (in blue) and the power input into the magnetosphere (P_α, in mauve). All data are all available 3-hourly values for the interval 1995–2017, inclusive and averages are taken in 36 bins of F of width 0.0278. The pink and cyan shaded errors are plus and minus one standard error in the means. In each case mean values of a generic index X in each F bin are normalized by dividing by the overall mean of X over the whole interval. The panels are for the geomagnetic indices: (a) am; (b) aσ-midnight; (c) aσ-dawn; (d) aσ-noon; (e) aσ-dusk; (f) aa_H; (g) Dst; (h) AU and (i) AL. Note that for the bottom row the y-scale has been expanded by a factor of 3.