Magnetic Connectivity of the Ecliptic Plane within 0.5 au: Potential Field Source Surface Modeling of the First Parker Solar Probe Encounter

Abstract

We compare magnetic field measurements taken by the FIELDS instrument on Parker Solar Probe (PSP) during it's first solar encounter to predictions obtained by Potential Field Source Surface (PFSS) modeling. Ballistic propagation 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 (107.5 R ) down to 0.16 AU (35.7 R ). 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 (R SS ) to the PFSS model finding that an extraordinarily low source surface height (1.3 − 1.5R ) 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 indicating plausible magnetic footpoints and offering context for future discussions of sources of the solar wind measured by PSP.

Coronal Electron Temperature Inferred from the Strahl Electrons in the Inner Heliosphere: Parker Solar Probe and Helios Observations

“…Oppositely, the bright regions in the image correspond to higher plasma densities, normally related to closed magnetic field loops. Similar plot has been shown in the work of Badman et al (2019), who use a PFSS model to map the magnetic field lines measured by the spacecraft back to the solar surface (see Figs. 5 & 8 in the referred article).…”

“…These observations imply that T s carries the information about the coronal electron temperature. The obtained values are in agreement with coronal temperatures measured using spectroscopy (David et al 1998), and the inferred solar wind source regions during the first orbit of PSP agree with the predictions using a PFSS model Badman et al 2019).…”

“…SWEAP in situ proton velocity measurements are used to perform this projection. The coloured lines show the magnetic field lines mapped from each of the sub spacecraft points down to the solar surface as predicted by the PFSS model (see Bale et al (2019); Badman et al (2019) for more details about the PFSS modelling). The polarity inversion line is shown in white.…”

“…8). Through comparison with the PFSS modelling of the magnetic field line topology during the first orbit of PSP presented in the study by Badman et al (2019), we crudely separated the strahl temperature data into 3 bins. The coldest T s (T s < 75 eV) were observed at times when measured magnetic field lines appear to connect to a bigger equatorial coronal hole encountered just after the first PSP perihelion.…”

“…The PSP trajectory is ballistically projected down to the corona (2 RS) to produce sub spacecraft points. The coloured lines denote magnetic field lines mapped from the sub spacecraft points to the solar surface as predicted by the PFSS model with source surface height 2 RS, the same as used inBale et al (2019);Badman et al (2019). The white line shows the PFSS neutral line.…”