Other
Scientific paper
Apr 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005an....326..227l&link_type=abstract
Astronomische Nachrichten, Vol.326, Issue 3, p.227-230
Other
5
Geomagnetic Field, Geodynamo, Stochastic Resonance
Scientific paper
Recently a signal with a period of 100 kyr in the distribution of residence times between reversals of the geomagnetic field has been suggested as signature of stochastic resonance. Here we test this suggestion by applying periodic modulations to a model of the geodynamo as a bistable oscillator, where stochastic fluctuations of the induction effect (multiplicative noise) lead to random transitions between the two polarity states of the supercritically excited fundamental axial dipole mode. By adding a weak periodic component either to the dynamo effect (multiplicative periodic term) or as a source term to the dynamo equation (additive periodic term) we demonstrate stochastic resonance. Depending on the multiplicative (additive) character of the periodic term, we find peaks at integer (half-integer) values of the applied period, superimposed on the otherwise Poissonian distribution of residence times. Especially the optimum resonance conditions for various mean times between reversals and various periodicities are derived. The periodic terms need to be about 0.1 in amplitude compared to the other terms in the dynamo equation to show the observed signatures of the magnetic field of the Earth. A sharp peak at the forcing frequency in the power spectrum of the dipole amplitude is only found in the additive case. As such a peak is absent in the Earth data, this rules for the multiplicative case. It is yet unclear what may cause such an effect to the geodynamo.
Consolini Giuseppe
de Michelis Paola
Lorito Stefano
Schmitt Denis
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