Long-term variations of turbulent transport coefficients in a solar-like convective dynamo simulation

TL;DR

This study analyzes a solar-like convective dynamo simulation over 60 magnetic cycles, revealing how turbulent transport coefficients vary long-term and influence phenomena like missing cycles and magnetic field confinement.

Contribution

It provides the first detailed analysis of long-term variations in turbulent transport coefficients in a solar-like dynamo simulation using the test-field method.

Findings

Reduction of αφφ precedes the missed cycle.

Enhanced downward turbulent pumping confines magnetic fields.

Turbulent magnetic diffusivities are quenched differently with depth.

Abstract

The Sun, aside from its eleven year sunspot cycle is additionally subject to long term variation in its activity. In this work we analyse a solar-like convective dynamo simulation, containing approximately 60 magnetic cycles, exhibiting equatorward propagation of the magnetic field, multiple frequencies, and irregular variability, including a missed cycle and complex parity transitions between dipolar and quadrupolar modes. We compute the turbulent transport coefficients, describing the effects of the turbulent velocity field on the mean magnetic field, using the test-field method. The test-field analysis provides a plausible explanation of the missing cycle in terms of the reduction of $\alpha_{\phi\phi}$ in advance of the reduced surface activity, and enhanced downward turbulent pumping during the event to confine some of the magnetic field at the bottom of the convection zone, where local maximum of magnetic energy is observed during the event. At the same time, however, a quenching of the turbulent magnetic diffusivities is observed, albeit differently distributed in depth compared to the other transport coefficients. Therefore, dedicated mean-field modelling is required for verification.