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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 10/11
Ann. Geophys., 12, 1065–1070, 1994
https://doi.org/10.1007/s00585-994-1065-5
© European Geosciences Union 1994
Ann. Geophys., 12, 1065–1070, 1994
https://doi.org/10.1007/s00585-994-1065-5
© European Geosciences Union 1994

  31 Aug 1994

31 Aug 1994

Long-term variations in the geomagnetic activity level Part II: Ascending phases of sunspot cycles

V. Mussino, O. Borello Filisetti, M. Storini, and H. Nevanlinna V. Mussino et al.

Abstract. Monthly averages of the Helsinki Ak-values have been reduced to the equivalent aa-indices to extend the aa-data set back to 1844. A periodicity of about five cycles was found for the correlation coefficient (r) between geomagnetic indices and sunspot numbers for the ascending phases of sunspot cycles 9 to 22, confirming previous findings based on a minor number of sunspot cycles. The result is useful to researchers in topics related to solar-terrestrial physics, particularly for the interpretation of long-term trends in geomagnetic activity during the past, and to forecast geomagnetic activity levels in the future.

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