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Geomagnetic activity during solar cycle 9 (1844–1856)
Author(s) -
Nevanlinna H.,
Ketola A.,
Häkkinen L.,
Viljanen A.,
Ivory K.
Publication year - 1993
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/93gl00836
Subject(s) - geomagnetic storm , sunspot , atmospheric sciences , storm , observatory , climatology , solar cycle 23 , solar cycle , declination , earth's magnetic field , physics , environmental science , meteorology , geology , astrophysics , solar wind , magnetic field , quantum mechanics
Ten‐minute values of declination observations carried out at the Helsinki observatory were used to analyze magnetic activity and storminess during 1844–1856 spanning solar cycle 9. Three‐hour K ‐indices and daily Ak ‐amplitudes were derived numerically from the data and compared with corresponding indices from the present Nurmijärvi magnetic observatory nearby. Helsinki magnetic activity data are based on homogeneous and reliable observations being thus utilizable for extending long activity series (like aa since 1868 onwards) backwards in time. Magnetic activity during 1844–1856 has been, on the average, on the same level as the activity at Nurmijärvi during the last four sunspot cycles in 1953–1992 but the occurrence of very large magnetic storms has been more frequent at Nurmijärvi. There have been about 300 magnetic storm days ( Ak ≥ 30) during cycle 9. The distribution of storm occurrence was double‐peaked within the cycle: in the rising (1847–48) and falling (1851–54) parts of the sunspot cycle substantially more magnetic storms appeared than during the years in between.