Physics
Scientific paper
Apr 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993georl..20..743n&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 20, no. 8, p. 743-746.
Physics
6
Geomagnetism, Magnetic Variations, Solar Cycles, Solar Terrestrial Interactions, Declination, Magnetic Storms, Periodic Variations, Solar Observatories
Scientific paper
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 Nurmijarvi magnetic observatory nearby. Helsinki magnetic activity data are based on homogeneous and reliable observations useful for extending long activity series backwards in time. Magnetic activity during 1844-1856 has been, on the average, on the same level as the activity at Nurmijarvi during the last four sunspot cycles in 1953-1992, but the occurrence of very large magnetic storms has been more frequent at Nurmijarvi. There have been about 300 magnetic storm days (Ak above 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.
Häkkinen L.
Ivory K.
Ketola Anneli
Nevanlinna Heikki
Viljanen Ari
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