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| Titel |
Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 3: Improved representation of solar cycle 11 |
| VerfasserIn |
M. Lockwood, H. Nevanlinna, M. Vokhmyanin, D. Ponyavin, S. Sokolov, L. Barnard, M. J. Owens, R. G. Harrison, A. P. Rouillard, C. J. Scott |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 32, no. 4 ; Nr. 32, no. 4 (2014-04-11), S.367-381 |
| Datensatznummer |
250121047
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| Publikation (Nr.) |
 copernicus.org/angeo-32-367-2014.pdf |
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| Zusammenfassung |
| 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 methods produce very similar
corrections which are here confirmed using newly digitised data from the
nearby St Petersburg observatory and also using declination data from
Helsinki. However, we show that the IDV index is, compared to later years,
too similar to sunspot number before 1872, revealing independence of the two
data series has been lost; either because the geomagnetic data used to
compile IDV has been corrected using sunspot numbers, or vice versa, or both.
We present corrected data sequences for both the IDV(1d) index and the
reconstructed IMF (interplanetary magnetic field). We also analyse the relationship between the derived
near-Earth IMF and the sunspot number and point out the relevance of the
prior history of solar activity, in addition to the contemporaneous value, to
estimating any "floor" value of the near-Earth interplanetary field. |
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