Long‐term variations of turbulent transport coefficients in a solarlike convective dynamo simulation

Abstract

The Sun, aside from its 11‐year sunspot cycle, is additionally subject to long‐term variation in its activity. In this work, we analyze a solarlike 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 αϕϕ 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 the 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 modeling is required for verification.