3 research outputs found
Magnetic connectivity of the ecliptic plane within 0.5 AU : PFSS modeling of the first PSP encounter
We compare magnetic field measurements taken by the FIELDS instrument on Parker Solar Probe (PSP) during its 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 PSPs first observations of the heliospheric magnetic field from 0.5 AU (107.5 Rs) down to 0.16 AU (35.7 Rs). 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 (RSS) to the PFSS model finding that an extraordinarily low source surface height (1.3-1.5Rs) 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
The contribution of alpha particles to the solar wind angular momentum flux in the inner heliosphere
This is the final version. Available from EDP Sciences via the DOI in this recordContext. An accurate assessment of the Sun’s angular momentum (AM) loss rate is an independent constraint for models that describe the rotation
evolution of Sun-like stars.
Aims. In-situ measurements of the solar wind taken by Parker Solar Probe (PSP), at radial distances of ∼ 28−55R , are used to constrain the solar
wind AM-loss rate. For the first time with PSP, this includes a measurement of the alpha particle contribution.
Methods. The mechanical AM flux in the solar wind protons (core and beam), and alpha particles, is determined as well as the transport of AM
through stresses in the interplanetary magnetic field. The solar wind AM flux is averaged over three hour increments, so that our findings more
accurately represent the bulk flow.
Results. During the third and fourth perihelion passes of PSP, the alpha particles contain around a fifth of the mechanical AM flux in the solar
wind (the rest is carried by the protons). The proton beam is found to contain ∼ 10−50% of the proton AM flux. The sign of the alpha particle AM
flux is observed to correlate with the proton core. The slow wind has a positive AM flux (removing AM from the Sun as expected), and the fast
wind has a negative AM flux. As with previous works, the differential velocity between the alpha particles and the proton core tends to be aligned
with the interplanetary magnetic field.
Conclusions. In future, by utilising the trends in the alpha-proton differential velocity, it may be possible to estimate the alpha particle contribution
when only measurements of the proton core are available. Based on the observations from this work, the alpha particles contribute an additional
10 − 20% to estimates of the solar wind AM-loss rate which consider only the proton and magnetic field contributions. Additionally, the AM flux
of the proton beam can be just as significant as the alpha particles, and so should not be neglected in future studies.European Union Horizon 202