Investigations of the solar dynamo within the framework of the Babcock-Leighton mechanism

by Simon Cloutier
Doctoral thesis
Date of Examination:2023-11-13
Date of issue:2024-06-13
Advisor:Prof. Dr. Laurent Gizon
Referee:Prof. Dr. Laurent Gizon
Referee:Prof. Dr. Andreas Tilgner
Persistent Address: http://dx.doi.org/10.53846/goediss-10521

 

 

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Abstract

English

Sunspots are dark blemishes on the surface of the Sun whose number waxes and wanes over the course of approximately eleven years. This solar cycle is believed to be powered by a hydromagnetic dynamo, whereby the interaction with rotation of flows inside the convection zone amplify magnetic fields against Ohmic dissipation, in such a way as to provoke regular polarity reversals. Despite intense research starting from the 1960s, the exact mode of operation of the solar dynamo is to this day still not ascertained with confidence. The aim of this dissertation is to help shed light on this enigma. We approach the problem from both the observational and theoretical angles in the context of the Babcock-Leighton mechanism for poloidal field regeneration. We make use of an axisymmetric kinematic mean-field dynamo model in which the large-scale flows are taken from recent helioseismic inversions. In contrast to most models in the literature, we do not prescribe a preference for emergences to take place at the observed low heliographic latitudes, requiring deep turbulent pumping. However, this linear model does not reproduce the so-called "rush to the poles", and a nonlinearity such as an emergence rate based on magnetic buoyancy is necessary to recover it, further providing a saturation mechanism. The depletion of toroidal field during flux emergence is also taken into account, and is shown to considerably slow down the cycle period. Furthermore, we studied the dynamo effect from the perspective of dynamo waves. This allowed us to better understand the role of flows and emergence loss.
Keywords: Sun: magnetic fields; Sun: activity; Sun: interior
 
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