A theoretical study of the build-up of the Sun's polar magnetic field by using a 3D kinematic dynamo model

TL;DR

This paper develops a 3D kinematic solar dynamo model to study the formation of the Sun's polar magnetic field, revealing new insights into flux transport and the impact of sunspot pairs on polar field evolution.

Contribution

It introduces a novel 3D dynamo model incorporating surface flux transport and analyzes the effects of sunspot pairs, including Hale's law violations, on polar magnetic field build-up.

Findings

Polar fields vanish due to upward advection of flux at low latitudes.

Anti-Hale sunspot pairs have limited impact on polar fields.

Surface flux transport insights need revision based on 3D modeling.

Abstract

We develop a three-dimensional kinematic self-sustaining model of the solar dynamo in which the poloidal field generation is from tilted bipolar sunspot pairs placed on the solar surface above regions of strong toroidal field by using the SpotMaker algorithm, and then the transport of this poloidal field to the tachocline is primarily caused by turbulent diffusion. We obtain a dipolar solution within a certain range of parameters. We use this model to study the build-up of the polar magnetic field and show that some insights obtained from surface flux transport (SFT) models have to be revised. We present results obtained by putting a single bipolar sunspot pair in a hemisphere and two symmetrical sunspot pairs in two hemispheres.We find that the polar fields produced by them disappear due to the upward advection of poloidal flux at low latitudes, which emerges as oppositely-signed radial flux and which is then advected poleward by the meridional flow. We also study the effect that a large sunspot pair, violating Hale's polarity law would have on the polar field. We find that there would be some effect---especially if the anti-Hale pair appears at high latitudes in the mid-phase of the cycle---though the effect is not very dramatic.