Supermodulation of the solar cycle
Résumé
There is evidence from record of cosmogenic radionuclides that the Sun's activity switches between periods of strong modulation with clusters of deep grand minima and periods of weaker modulation. By considering dynamo action driven by three-dimensional rotating anelastic convection in a spherical shell, we demonstrate how interactions between convection, differential rotation and magnetic fields may lead to modulation of the basic cycle of an oscillatory dynamo. For some parameters, Type 1 modulation occurs by the transfer of energy between modes of different symmetries with little change in the overall amplitude; for other parameters, the modulation is of Type 2 where the amplitude is significantly affected (leading to grand minima in activity) without significant changes in symmetry. Most importantly we identify the presence of supermodulation in the solutions where the activity switches chaotically between Type 1 and Type 2 modulation; this is believed to be characteristic of the long term modulation of the solar activity.
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