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Fig. 4


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Scatter plots of geomagnetic indices as a function of normalized power input into the magnetosphere computed from near-Earth solar wind observation, P α /〈P α all, where the average is over the full period considered (1995–2017, inclusive). The left hand panels are for daily means, the right hand panels for annual means. The top panels are for the ap index, the middle for aa index, the bottom for am index. For the daily data, linear regression fits are shown for: (red line) 91 days around the June solstice; (blue line) 91 days around the December solstice; and (orange line) 91 days around either equinox). For annual means the cyan lines are linear regression fits for all data. The number of valid daily P α data points is N = 8375 (an availability of 99.7%) and for annual means is N = 23. The best-fit coupling exponent used to generate P α is α = 0.44 for am and aa and α = 0.48 for ap. The linear correlation coefficients, r, and the Root Mean Square (RMS) linear fit residual ε (as a ratio of the overall mean value of the index) are given in each panel.

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