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| Titel |
Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 1: A new geomagnetic data composite |
| VerfasserIn |
M. Lockwood, L. Barnard, H. Nevanlinna, M. J. Owens, R. G. Harrison, A. P. Rouillard, C. J. Davis |
| 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 ; 31, no. 11 ; Nr. 31, no. 11 (2013-11-18), S.1957-1977 |
| Datensatznummer |
250086144
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| Publikation (Nr.) |
 copernicus.org/angeo-31-1957-2013.pdf |
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| Zusammenfassung |
| We present a new composite of geomagnetic activity which is designed to be
as homogeneous in its construction as possible. This is done by only combining
data that, by virtue of the locations of the source observatories used, have
similar responses to solar wind and IMF (interplanetary magnetic field) variations. This will enable us (in
Part 2, Lockwood et al., 2013a) to use the new index to reconstruct the interplanetary
magnetic field, B, back to 1846 with a full analysis of errors. Allowance is
made for the effects of secular change in the geomagnetic field. The
composite uses interdiurnal variation data from Helsinki for 1845–1890
(inclusive) and 1893–1896 and from Eskdalemuir from 1911 to the present. The
gaps are filled using data from the Potsdam (1891–1892 and 1897–1907) and
the nearby Seddin observatories (1908–1910) and intercalibration achieved
using the Potsdam–Seddin sequence. The new index is termed IDV(1d) because it
employs many of the principles of the IDV index derived by Svalgaard and Cliver (2010), inspired by
the u index of Bartels (1932); however, we revert to using one-day (1d) means, as
employed by Bartels, because the use of near-midnight values in IDV introduces
contamination by the substorm current wedge auroral electrojet, giving noise and a
dependence on solar wind speed that varies with latitude. The composite is
compared with independent, early data from European-sector stations,
Greenwich, St Petersburg, Parc St Maur, and Ekaterinburg, as well as the
composite u index, compiled from 2–6 stations by Bartels, and the IDV index of
Svalgaard and Cliver. Agreement is found to be extremely good in all cases,
except two. Firstly, the Greenwich data are shown to have gradually degraded
in quality until new instrumentation was installed in 1915. Secondly, we
infer that the Bartels u index is increasingly unreliable before about 1886
and overestimates the solar cycle amplitude between 1872 and 1883 and this
is amplified in the proxy data used before 1872. This is therefore also true
of the IDV index which makes direct use of the u index values. |
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