Improving boundary Br maps for global coronal magnetic field models

The solar-surface B_r maps are one of the key input data to the heliophysics models. In particular, the potential-field source-surface (PFSS) model relies on the boundary B_r map, and its solutions are widely used in the field of solar physics (for example, in the WSA solar wind speed prediction model and MHD models).

To specify the boundary condition of the PFSS model, the so-called synoptic map is widely used. A synoptic map is constructed by assembling the central meridian slits of full-disk line-of-sight (LoS) observations made over one Carrington rotation period. The LoS values are converted to the B_r component through the radial-field assumption (or mu-correction method). However, these procedures cannot prevent some possible artifacts: The near horizontal magnetic field at penumbra regions often appears as the false opposite polarity in the LoS magnetogram, and this false polarity remains through the radial-field assumption. The map simply collecting the central meridian slits over one Carrington rotation period can hardly represent the solar-surface condition at arbitrary instants of interest.

We recently developed a data process suite to mitigate these issues. In this suite, the false polarity can be corrected with the assistance from our new potential field model that yields high-resolution solution matching the LoS magnetogram data instead of B_r from the radial-field assumption. The ADAPT model provides a theory-based temporally seamless inference of the B_r distribution over the whole solar surface.

For testing the combination of these features, the derived time-series whole-Sun maps are input to the WSA solar wind prediction model. We examine differences in the open field footpoints of the PFSS solutions, and the predicted solar wind speed at 1 AU derived from the time series of the new B_r maps and the standard synoptic maps.

This work is partially supported by NASA HSWO2R Grant 80NSSC19K0007.