Authors: Graham Barnes (NWRA), Marc L. DeRosa (LMSAL), Stephan G. Heinemann (Department of Physics, University of Helsinki), Carl J. Henney (AFRL SVD), Shaela I. Jones (NASA GSFC), Bibhuti Kumar Jha (SwRI), Jon A. Linker (Predictive Science Inc.), Evangelia Samara (NASA GSFC), Vishal Upendran (LMSAL), Lisa Upton (SwRI), Charles. N. Arge (NASA GSFC), Ronald M. Caplan (Predictive Science Inc.), David F. Fouhey (NYU, Courant Institute of Mathematical Sciences & Tandon School of Engineering), Mathew J. Owens (Space and Atmospheric Electricity Group, Department of Meteorology, University of Reading), Manuela Temmer (Institute of Physics, University of Graz), Sam Schonfeld (AFRL SVD)

High quality global maps of the magnetic field at the surface of the Sun are essential for successful modeling of the Sun’s corona and out into the heliosphere. To construct such maps, it is common to use a Surface Flux Transport (SFT) model to estimate the evolution of the photospheric magnetic field between times when it is observed. A variety of SFT models have been developed, including the Air Force Data Assimilative Photospheric Flux Transport model (ADAPT; Hickman et al. 2015), the Advective Flux Transport model (AFT; Upton & Hathaway 2014), the combined surface flux transport and helioseismic Far-side Active Region Model (FARM; Yang et al. 2024), the High performance Flux Transport model (HipFT; Caplan et al. 2025), the Surface Transport of B by E model (STrOBE), and the SFT model available through SolarSoft (SSW-PFSS; Schrijver 2001). All these models have the same goal but different implementation that can result in meaningful differences in the resulting global maps.

Because the magnetic field on the entire solar surface is not routinely observed, it is difficult to directly validate how well the SFT models work in capturing the evolution of the magnetic field. Thus, most validation efforts rely on further modeling to predict observable properties. The most commonly used comparisons are between observations of the locations of coronal holes, areas of low EUV emission, with the location of open magnetic field (i.e., magnetic field lines that do not close on the surface of the Sun), and between observed in-situ measurements of the solar wind properties (speed and magnetic field polarity) and the predicted solar wind properties. We present here initial results from an ISSI team convened to make systematic, quantitative comparisons against observations of the predictions from a variety of SFT models.

We thank the International Space Science Institute (ISSI) for providing support for this work.