Buoyancy-induced time delays in Babcock-Leighton flux-transport dynamo models

TL;DR

This paper explores how magnetic buoyancy-induced time delays in Babcock-Leighton dynamo models cause significant cycle modulation, offering a more realistic explanation for solar cycle variability aligned with observations.

Contribution

It introduces a modified Babcock-Leighton model incorporating delay effects from flux tube rise times based on 3D MHD results, revealing their impact on solar cycle modulation.

Findings

Time delays cause large amplitude modulation of solar cycles.

Cycle modulation arises from nonlinear delay effects dependent on magnetic field strength.

The model produces butterfly diagrams more consistent with observations.

Abstract

The Sun is a magnetic star whose cyclic activity is thought to be linked to internal dynamo mechanisms. A combination of numerical modelling with various levels of complexity is an efficient and accurate tool to investigate such intricate dynamical processes. We investigate the role of the magnetic buoyancy process in 2D Babcock-Leighton dynamo models, by modelling more accurately the surface source term for poloidal field. Methods. To do so, we reintroduce in mean-field models the results of full 3D MHD calculations of the non-linear evolution of a rising flux tube in a convective shell. More specifically, the Babcock-Leighton source term is modified to take into account the delay introduced by the rise time of the toroidal structures from the base of the convection zone to the solar surface. We find that the time delays introduced in the equations produce large temporal modulation of the cycle amplitude even when strong and thus rapidly rising flux tubes are considered. Aperiodic modulations of the solar cycle appear after a sequence of period doubling bifurcations typical of non-linear systems. The strong effects introduced even by small delays is found to be due to the dependence of the delays on the magnetic field strength at the base of the convection zone, the modulation being much less when time delays remain constant. We do not find any significant influence on the cycle period except when the delays are made artificially strong. A possible new origin of the solar cycle variability is here revealed. This modulated activity and the resulting butterfly diagram are then more compatible with observations than what the standard Babcock-Leighton model produces.