Secular behaviour of geomagnetic indices IHV, C9, aa since 1901 and presumed rising of solar open magnetic field flux

Abstract

We examine long-term series of IHV and C9 geomagnetic indices calculated from the data derived during the 20th century in St.-Petersburg, Pavlovsk, Swider, Cheltenham, Fredericksburg, Kakioka, and Honolulu in order to verify the conclusion of Lockwood et al. [8] that the total magnetic flux leaving the Sun increased by a factor of 2.3 since 1901. It was supported on the analysis of aa geomagnetic index which shows a drift upward from the 12th–13th solar cycle to the 22nd cycle. The mean level of the annual averages of indices used here have been approximately constant or showed the clearly smaller rising than aa drift upward from 1901 till 1960. We conclude that the double rising of solar magnetic flux during the 20th century is questionable.