Successfully Reproducing Solar Orbiter Polar Field Observations with a Surface Flux Transport Model

Abstract

The solar polar field plays a fundamental role in predicting solar-cycle strength and determines the large-scale structure of the heliospheric magnetic field. The High Resolution Telescope of the Polarimetric and Helioseismic Imager aboard Solar Orbiter (SO/PHI-HRT) provides unprecedented observations of the solar polar regions, as Solar Orbiter currently reaches heliographic latitudes of up to $\pm 17^{\circ }$, about $10^{\circ }$ higher than those accessible from near-ecliptic observations. Using these observations to further test surface flux transport models, we present a successful simulation of the SO/PHI-HRT observations, reproducing the latitudinal profiles of the longitudinally averaged radial magnetic field in both polar regions. This result is achieved using the meridional-flow profile proposed by \citet{WangRH2026}, which also reproduces the evolution of the axial dipole strength, magnetic butterfly diagram, and high-latitude magnetic fields observed by SDO/HMI during Solar Cycle 25. We further compare simulations using this profile with simulations employing two representative meridional-flow profiles characterized by different peak latitudes. The latter fail to reproduce the observed high-latitude and polar fields. The comparison demonstrates that the meridional-flow profile strongly regulates poleward flux transport and the resulting polar-field evolution. Profiles peaking at higher latitudes produce stronger flux surges, and stronger and more concentrated polar fields. These results provide new constraints on the large-scale solar meridional flow.

9 pages, 5 figures, accepted by ApJ; comments are welcome