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Title:
Does the aa Index Really Imply a Rich Doubling of the Heliospheric Magnetic Field during the Last 100 Years?
Authors:
Mursula, K.; Martini, D.
Affiliation:
AA(University of Oulu, Linnanmaa, Oulu, 90014 Finland ; ), AB(University of Oulu, Linnanmaa, Oulu, 90014 Finland ; GGKI, POB 5, Sopron, 9401 Hungary ; )
Publication:
American Geophysical Union, Fall Meeting 2004, abstract #SH53B-0310
Publication Date:
12/2004
Origin:
AGU
AGU Keywords:
7524 Magnetic fields, 7537 Solar and stellar variability, 2784 Solar wind/magnetosphere interactions
Bibliographic Code:
2004AGUFMSH53B0310M

Abstract

It is known since long that the long-term geomagnetic activity presented by the aa index increases considerably during the last 100 years. This increase, together with the more recent in situ measurements of the heliospheric parameters, has been used to claim that the heliospheric magnetic field has more than doubled during the last centennium. Here we reanalyze the implications of the centennial increase of the aa index by studying the relation between the various heliospheric parameters and geomagnetic activity. We show that, while the heliospheric magnetic field does increase during the last 100 years, the earlier estimate on this increase is grossly exaggerated. Moreover, since serious concern has recently been raised on the long-term consistency of the aa index, we have reanalyzed geomagnetic activity during the last 100 years using data from several stations and extracted a new centennial index C of global geomagnetic activity. We compare the implications of this new index and the aa index for the last 100 years.
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