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In the concluding paper of this tetralogy, we here use the differentgeomagnetic activity indices to reconstruct the near-Earth interplanetarymagnetic field (IMF) and solar wind flow speed, as well as the open solarflux (OSF) from 1845 to the present day. The differences in how the variousindices vary with near-Earth interplanetary parameters, which are hereexploited to separate the effects of the IMF and solar wind speed, are shownto be statistically significant at the 93% level or above.Reconstructions are made using four combinations of different indices,compiled using different data and different algorithms, and the results arealmost identical for all parameters. The correction to the aa index requiredis discussed by comparison with the Ap index from a more extensivenetwork of mid-latitude stations. Data from the Helsinki magnetometer stationis used to extend the aa index back to 1845 and the results confirmed bycomparison with the nearby St Petersburg observatory. The optimum variations,using all available long-term geomagnetic indices, of the near-Earth IMF andsolar wind speed, and of the open solar flux, are presented; all with±2σ uncertainties computed using the Monte Carlo techniqueoutlined in the earlier papers. The open solar flux variation derived isshown to be very similar indeed to that obtained using the method of Lockwoodet al. (1999)

annales geophysicae

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 4: Near-Earth solar wind speed, IMF, and open solar flux