Authors: Jon A. Linker (Predictive Science Inc.), Cooper Downs (Predictive Science Inc.), Ronald M. Caplan (Predictive Science Inc.), James Turtle (Predictive Science Inc.), Pete Riley (Predictive Science Inc.), Artem Ulyanov (Max Planck Institute for Solar System Research), & Gherardo Valori (Max Planck Institute for Solar System Research)

The Sun’s photospheric magnetic field expands outward to fill the corona and heliosphere. The polar magnetic fields can profoundly affect the topology and structure of the entire coronal magnetic field, and, particularly at solar minimum, contributes disproportionately to the open magnetic flux. It is difficult to accurately measure the polar magnetic field from the ecliptic plane, where, until recently, all observations have been made. Surface Flux Transport (SFT) models incorporate the processes by which magnetic flux is transported and dispersed across the solar surface. They can assimilate magnetograms and predict the flux on unobserved portions of the Sun, including the poles. Global maps of the solar magnetic field from SFTs are frequently used in lieu of standard synoptic maps, in part because they predict the polar values. In the past year, Solar Orbiter ascended to nearly 17 degrees heliographic latitude, allowing unprecedented measurements of the solar polar magnetic field by the PHI instrument. We employ the Open-Source Flux Transport (OFT) model (https://github.com/predsci/OFT) to assimilate GONG, HMI line-of-sight (LOS) and HMI vector measurements and simulate the surface flux of the Sun over many years. We compare the polar magnetic flux predicted by the model for different realizations and different data sources around the time period of the Solar Orbiter North polar pass in 2025 with the PHI measurements.

Work supported by NASA and NSF.