Evidence for a long-term variation of the dynamo action responsible for the solar magnetic cycle |
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| Authors: | I Lopes D Passos |
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| Institution: | Centro Multidisciplinar de Astrofísica, Instituto Superior Técnico, Av Rovisco Pais, 1049-001 Lisboa, Portugal;Departamento de Física, Universidade de Évora, Colégio António Luis Verney, 7002-554 Évora, Portugal |
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| Abstract: | By using the sunspot time series as a proxy, we have made a detailed analysis of the mean solar magnetic field over the last two and half centuries, by means of a reconstruction of its phase space. We find evidence of a long-term trend variation of some of the solar physical processes (over a few decades) that might be responsible for the apparent erratic behaviour of the solar magnetic cycle. The analysis is done by means of a careful study of the axisymmetric dynamo model equations, where we show that the temporal counterpart of the magnetic field can be described by a self-regulated two-dimensional dynamic system, usually known as a Van der Pol–Duffing oscillator. Our results suggest that during the last two and half centuries, the velocity of the meridional flow, v p, and the efficiency of the α mechanism responsible for the conversion of toroidal magnetic field into poloidal magnetic field might have suffered variations that can explain the observed variability in the solar cycle. |
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| Keywords: | Sun: activity Sun: fundamental parameters Sun: magnetic fields sunspots |
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