# The need for active region disconnection in 3D kinematic dynamo simulations

## TL;DR

This paper investigates the importance of active region disconnection in 3D kinematic dynamo simulations, showing that proper modeling of active region connectivity affects surface flux evolution and solar cycle sustainability.

## Contribution

It introduces the concept that active region disconnection is crucial in 3D dynamo models and explores how diffusivity influences flux evolution and cycle sustainability.

## Key findings

- Increasing diffusivity improves surface flux evolution.
- Enhanced diffusivity prevents dynamo self-sustenance in full cycle simulations.
- Active region disconnection is essential for accurate solar cycle modeling.

## Abstract

In this paper we address a discrepancy between the surface flux evolution in a 3D kinematic dynamo model and a 2D surface flux transport model that has been closely calibrated to the real Sun. We demonstrate that the difference is due to the connectivity of active regions to the toroidal field at the base of the convection zone, which is not accounted for in the surface-only model. Initially, we consider the decay of a single active region, firstly in a simplified Cartesian 2D model and subsequently the full 3D model. By varying the turbulent diffusivity profile in the convection zone, we find that increasing the diffusivity - so that active regions are more rapidly disconnected from the base of the convection zone - improves the evolution of the surface field. However, if we simulate a full solar cycle, we find that the dynamo is unable to sustain itself under such an enhanced diffusivity. This suggests that in order to accurately model the solar cycle, we must find an alternative way to disconnect emerging active regions, whilst conserving magnetic flux.