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Duhau & Chen 2002
Duhau, S. and Chen, C. Y. (2002). The sudden increase of solar and geomagnetic activity after 1923 as a manifestation of a non-linear solar dynamo. Geophysical Research Letters 29: doi: 10.1029/2001GL013953. issn: 0094-8276.

There are some indications that the coupling function between the polar and the toroidal solar magnetic field strengths are time dependent. Therefore, as proxy data of these strengths, the relationship between long-term modulation of solar and geomagnetic activity is analyzed here by means of a wavelet multi-resolution analysis of yearly means of sunspot number and geomagnetic index aa since 1844. It is found that aa index and relative sunspot number long-term modulations oscillate around constant levels that have increased to be 1.9 and 1.6, respectively of its values prior 1923. The oscillations of the aa and Rz long-term modulation appear to be well represented by the superposition of a decadal cycle and the Gleissberg cycle. The amplitude ratio and the phase shift between the Rz and aa decadal cycles changed sharply at year 1923, and the Gleissberg cycle was interrupted to be restarted at year 1949. The synchronicity of these changes with temporal changes in several solar and solar-terrestrial variables indicates that the non-linear nature of the solar dynamo has lead to a major change of its background state after 1923.

BACKGROUND DATA FILES

Abstract

Keywords
Interplanetary Physics, Solar cycle variations, Global Change, Solar variability, Solar Physics, Astrophysics, and Astronomy, Solar and stellar variability, Solar Physics, Astrophysics, and Astronomy, Magnetic fields
Journal
Geophysical Research Letters
http://www.agu.org/journals/gl/
Publisher
American Geophysical Union
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