Magnetic connectivity of the ecliptic plane within 0.5 AU : PFSS modelling of the early PSP encounters

We compare Parker Solar Probe (PSP) FIELDS early magnetic field measurements to predictions obtained by Potential Field Source Surface modeling (PFSS). Ballistic propagation (Parker spiral assumption) is used to connect the spacecraft to the source surface. Despite the simplicity of the model, our results show striking agreement with PSP's first observations of the heliospheric magnetic field from 0.5 AU down to 0.16 AU. Further, we show the robustness of the agreement is improved both by allowing the photospheric input to the model to vary in time, and by advecting the field from PSP down to the PFSS model domain using in situ PSP/SWEAP measurements of the solar wind speed instead of assuming it to be constant with longitude and latitude. We also explore the source surface height parameter to the PFSS model: Overall, we find evidence that a lower source surface height (< 2 solar radii) provides improvements to the prediction. We find for PSP Encounter 1 (Nov. 2018) that an extraordinarily low source surface height (1.3-1.5 solar radii) predicts observed small scale polarity inversions which are otherwise washed out with regular modeling parameters. Finally, we extract field line traces from these models. By overlaying these on EUV images we observe magnetic connectivity to various equatorial and mid-latitude coronal holes, providing a sanity check and offering context for future discussions of sources of the solar wind measured by PSP.