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Superstorms in various geomagnetic indices
Ponyavin D.I., Terekhin S.N.,
Intensity of geomagnetic storms can be determined by using classical Dst index of geomagnetic activity that is only available since 1957. Statistics of extremely large geomagnetic storms (superstorms) are obviously inconsistent due to short period of Dst observations. We have compared various geomagnetic indices (Ap, AA, C9 and other proxies) in order to find their interrelations during extreme geomagnetic events and extend statistics to the past. Solar cycle and seasonal changes of superstorm occurrence rate are detected and discussed.