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Long-term variations in the geomagnetic activity level Part II: Ascending phases of sunspot cycles |
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| Authors: | V Mussino O Borello Filisetti M Storini H Nevanlinna |
| Institution: | 1. Dipartimento di Fisica-Politecnico, Cso. Duca degli Abruzzi 24, I-10129, Torino, Italy 2. Raggi Cosmici-I.F.S.I.-CNR, c/o Dip. di Fisica-Univ. La Sapienza, P.le A. Moro 2, I-00185, Roma, Italy 3. Finnish Meteorological Institute, P.O. Box 503, SF-00101, Helsinki, Finland |
| 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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