71.
We apply a Kuramoto model of nonlinear coupled oscillators to the simulation of slow variations of the phase difference between sunspot number [
R I ] and geomagnetic indices [aa and
ζ]. The Kuramoto model is described for the particular case of two oscillators connected by symmetric coupling with quasi-stationary behavior, and its properties are investigated. By solving an inverse problem, we reconstruct the evolution of the couplings between pairs of indices [
R I and aa,
R I and
ζ, aa and
ζ], and interpret these in terms of the physics of the solar dynamo. The de-correlation between
R I and geomagnetic indices found in
Solar Cycle 20 by Le Mouël
et al. (
J. Geophys. Res. 117, A09103,
2012) is successfully reproduced by the Kuramoto model and corresponds to the alternation of the leading oscillator. Application of the Kuramoto model to the cross-correlations [
C(
R I ,
ζ) and
C(aa,
ζ)] for
ζ-indices computed in eight geomagnetic stations shows the latitudinal dependence of the mean phase difference. We discuss these results in terms of the solar-wind contribution to local geomagnetic indices [
ζ].
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