Delayed Babcock-Leighton dynamos in the diffusion-dominated regime

TL;DR

This paper introduces a non-linear time delay in Babcock-Leighton solar dynamo models, demonstrating it can produce realistic solar cycle features in high-diffusivity regimes, unlike traditional models.

Contribution

It is the first to incorporate a non-linear temporal delay based on flux tube rise times, revealing new solution families and improved solar cycle modeling in diffusion-dominated regimes.

Findings

Delayed solutions exhibit longer periods and self-quenching behavior.

Non-linear delay restores equatorward migration at high diffusivities.

Models with delay match observed solar butterfly diagrams.

Abstract

Context. Solar dynamo models of Babcock-Leighton type typically assume the rise of magnetic flux tubes to be instantaneous. Solutions with high-magnetic-diffusivity have too short periods and a wrong migration of their active belts. Only the low-diffusivity regime with advective meridional flows is usually considered. Aims. In the present paper we discuss these assumptions and applied a time delay in the source term of the azimuthally averaged induction equation. This delay is set to be the rise time of magnetic flux tubes which supposedly form at the tachocline. We study the effect of the delay, which adds to the spacial non-locality a non-linear temporal one, in the advective but particularly in the diffusive regime. Methods. Fournier et al. (2017) obtained the rise time according to stellar parameters such as rotation, and the magnetic field strength at the bottom of the convection zone. These results allowed us to constrain the delay in the mean-field model used in a parameter study. Results. We identify an unknown family of solutions. These solutions self-quench, and exhibit longer periods than their non-delayed counterparts. Additionally, we demonstrate that the non-linear delay is responsible for the recover of the equatorward migration of the active belts at high turbulent diffusivities. Conclusions. By introducing a non-linear temporal non-locality (the delay) in a Babcock-Leighton dynamo model, we could obtain solutions quantitatively comparable to the solar butterfly diagram in the diffusion-dominated regime.