Implications of Different Solar Photospheric Flux-Transport Models for Global Coronal and Heliospheric Modeling

TL;DR

This study compares two solar surface-flux transport models to understand their impact on predicting the solar magnetic field, coronal structure, and solar wind, revealing cycle-dependent differences and the influence of model assumptions.

Contribution

It provides a comparative analysis of different surface-flux transport models and their effects on solar and heliospheric predictions across the solar cycle.

Findings

Models show cycle-dependent agreement and differences.

Transient discrepancies occur during active region rotations.

Differences are mainly due to model assumptions, not stochastic flux evolution.

Abstract

The concept of surface-flux transport (SFT) is commonly used in evolving models of the large-scale solar surface magnetic field. These photospheric models are used to determine the large-scale structure of the overlying coronal magnetic field, as well as to make predictions about the fields and flows that structure the solar wind. We compare predictions from two SFT models for the solar wind, open magnetic field footpoints, and the presence of coronal magnetic null points throughout various phases of a solar activity cycle, focusing on the months of April in even-numbered years between 2012 and 2020, inclusive. We find that there is a solar cycle dependence to each of the metrics considered, but there is not a single phase of the cycle in which all the metrics indicate good agreement between the models. The metrics also reveal large, transient differences between the models when a new active region is rotating into the assimilation window. The evolution of the surface flux is governed by a combination of large scale flows and comparatively small scale motions associated with convection. Because the latter flows evolve rapidly, there are intervals during which their impact on the surface flux can only be characterized in a statistical sense, thus their impact is modeled by introducing a random evolution that reproduces the typical surface flux evolution. We find that the differences between the predicted properties are dominated by differences in the model assumptions and implementation, rather than selection of a particular realization of the random evolution.