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Fig. 2.


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Yearly rate of G1 to G4 storm days during the first 4 years of solar cycles 17–24; the symbol indicates the cycle number (blue squares for cycle 24). Error bars are given by the square root of the number of storm days. Note the tendency for the storm rate in year 4 to fall, associated with the decline in geomagnetic activity around solar maximum in the “Gnevyshev gap”.

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