Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 3: Improved representation of solar cycle 11

M. Lockwood, H. Nevanlinna, M. Vokhmyanin, D. Ponyavin, S. Sokolov, L. Barnard, M.J. Owens, R.G. Harrison, A.P. Rouillard, C.J. Scott

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

Svalgaard (2014) has recently pointed out that the calibration of the Helsinki magnetic observatory's H component variometer was probably in error in published data for the years 1866–1874.5 and that this makes the interdiurnal variation index based on daily means, IDV(1d), (Lockwood et al., 2013a), and the interplanetary magnetic field strength derived from it (Lockwood et al., 2013b), too low around the peak of solar cycle 11. We use data from the modern Nurmijarvi station, relatively close to the site of the original Helsinki Observatory, to confirm a 30% underestimation in this interval and hence our results are fully consistent with the correction derived by Svalgaard. We show that the best method for recalibration uses the Helsinki Ak (H) and aa indices and is accurate to ±10%. This makes it preferable to recalibration using either the sunspot number or the diurnal range of geomagnetic activity which we find to be accurate to ±20%. In the case of Helsinki data during cycle 11, the two recalibration meth
Original languageEnglish
Pages (from-to)367-381
Number of pages15
JournalAnnales Geophysicae
Volume32
Issue number4
DOIs
StatePublished - 2014

Keywords

  • Geomagnetism and palaeomagnetism (time variations, secular and long term
  • instruments and technique) – interplanetary physics (interplanetary magnetic fields)

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