Solar Polar Flux Redistribution based on Observed Coronal Holes

TL;DR

This study uses observed coronal holes to improve the accuracy of global solar magnetic field maps and solar wind predictions, demonstrating that polar flux modifications enhance model predictions across different heliospheric locations.

Contribution

The paper introduces a method to incorporate observed coronal holes into magnetic maps, improving the accuracy of solar and heliospheric models without relying on polar field observations.

Findings

Polar flux modifications improve CH and SW prediction accuracy.

Choice of domain affects WSA model predictions.

Low-latitude magnetic fields significantly influence polar CH boundaries.

Abstract

We explore the use of observed polar coronal holes (CHs) to constrain the flux distribution within the polar regions of global solar magnetic field maps in the absence of reliable quality polar field observations. Global magnetic maps, generated by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model, are modified to enforce field unipolarity thresholds both within and outside observed CH boundaries. The polar modified and unmodified maps are used to drive Wang-Sheeley-Arge (WSA) models of the corona and solar wind (SW). The WSA predicted CHs are compared with the observations, and SW predictions at the WIND and Ulysses spacecraft are also used to provide context for the new polar modified maps. We find that modifications of the polar flux never worsen and typically improve both the CH and SW predictions. We also confirm the importance of the choice of the domain over which WSA generates the coronal magnetic field solution but find that solutions optimized for one location in the heliosphere can worsen predictions at other locations. Finally, we investigate the importance of low-latitude (i.e., active region) magnetic fields in setting the boundary of polar CHs, determining that they have at least as much impact as the polar fields themselves.