Convective dynamo action in a spherical shell: symmetries and modulation

TL;DR

This paper investigates how complex interactions between convection, rotation, and magnetic fields in a spherical shell can lead to various modulation behaviors in dynamo action, including chaotic switching between different activity states, relevant to solar phenomena.

Contribution

It demonstrates the existence of multiple modulation types and supermodulation in a spherical dynamo model, highlighting mechanisms potentially responsible for solar activity variability.

Findings

Identification of Type 1 and Type 2 modulation mechanisms.

Discovery of supermodulation with chaotic switching.

Relevance to solar activity cycles.

Abstract

We consider dynamo action driven by three-dimensional rotating anelastic convection in a spherical shell. Motivated by the behaviour of the solar dynamo, we examine the interaction of hydromagnetic modes with different symmetries and demonstrate how complicated interactions between convection, differential rotation and magnetic fields may lead to modulation of the basic cycle. 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 an important process in solar activity.