Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1980
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1980apj...235..625y&link_type=abstract
Astrophysical Journal, Part 1, vol. 235, Jan. 15, 1980, p. 625-649.
Astronomy and Astrophysics
Astrophysics
6
Astrophysics, Dynamo Theory, Geomagnetism, Magnetic Field Inversions, Polarity, Solar Terrestrial Interactions, Magnetic Field Configurations, Magnetohydrodynamics, Nonlinear Equations, Time Lag, Toroids
Scientific paper
An autonomous mechanism for the polarity reversals of steady dynamos in a rotating spherical geometry is discovered in the solutions of the nonlinear dynamo equation with a time-delayed feedback process. The reversals take place automatically through intermittent excitation of dynamo waves of short durations in long lasting steady phases. The time delay in the feedback process gives rise to an imbalance between the dynamo and the diffusion processes and to an alternate dominance of the dynamo or the diffusion process in the solutions. The steady phases of the present reversal model are characterized by an automatic suppression of the dynamo process by a strong magnetic field created in the preceding oscillatory transition phases. The resulting field configuration of a resistive decay of each poloidal or toroidal component in such a steady phase is similar to that of a stationary steady dynamo which can be achieved by the exact balance between the dynamo and the diffusion processes in the case of no time delay. In the resistive steady phases, however, there can be two kinds of polarity relations between the two components, which gives rise to several kinds of polarity reversals. This autonomous mechanism is proposed as a model of the geomagnetic reversals. Basic properties of the model, sensitive to the structure of the fluid motions and to the multiplicity of the delay time parameter, are discussed in parallel with the observed characteristics of the paleomagnetic reversals of the Earth.
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