Resonance in Forced Flux Transport Dynamos

TL;DR

This paper demonstrates that flux-transport dynamo models can exhibit resonance effects depending on flow speeds and alpha-effect parameters, impacting solar cycle predictions and potentially observable in more realistic, variable models.

Contribution

It reveals that simple layered flux-transport dynamos can resonate under certain conditions, influencing magnetic field amplitudes and solar cycle forecasts.

Findings

Resonance depends on flow speed and alpha-effect parameters.

Resonance can cause large amplitude variations in magnetic fields.

Effect persists across different layer configurations.

Abstract

We show that simple 2 and 3-layer flux-transport dynamos, when forced at the top by a poloidal source term, can produce a widely varying amplitude of toroidal field at the bottom, depending on how close the meridional flow speed of the bottom layer is to the propagation speed of the forcing applied above the top layer, and how close the amplitude of the $\alpha$-effect is to two values that give rise to a resonant response. This effect should be present in this class of dynamo model no matter how many layers are included. This result could have implications for the prediction of future solar cycles from the surface magnetic fields of prior cycles. It could be looked for in flux-transport dynamos that are more realistic for the Sun, done in spherical geometry with differential rotation, meridional flow and $\alpha$-effect that vary with latitude and time as well as radius. Because of these variations, if resonance occurs, it should be more localized in time, latitude and radius.