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Annual variations in geomagnetic indices and power input into the magnetosphere: (left) the AaH index means for 1868–2017; (middle) Dst index (1959–2017) and (right) daily the power input into the magnetosphere Pα (1995–2017). In the top panels, the black lines show the mean values in 36 equal-width bins of fraction of time-of-year, F (roughly 10 days width) and the grey areas are plus and minus one standard deviation: (a) 〈AaH〉; (b) 〈Dst〉; and (c) 〈Pα〉. The lower panels show the variation of the number of days in which the daily means exceed the (blue) 90-percentile, (orange) 95-percentile, and (mauve) 99-percentile (d), (e) and (f) being for AaH, Dst and Pα, respectively. The thin vertical lines mark the equinoxes (the times of the peaks in the equinoctial variation) and the grey and cyan are variations predicted by the Russell-McPherron and equinoctial effect, respectively, scaled in amplitude to match the observed variations so as to reveal waveform and phase differences.

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