Exploring Solar Wind Origins and Connecting Plasma Flows from the Parker Solar Probe to 1 au: Nonspherical Source Surface and Alfvénic Fluctuations

Abstract

Abstract The magnetic field measurements of the FIELDS instrument on the Parker Solar Probe ( PSP ) have shown intensities, throughout its first solar encounter, that require a very low source surface (SS) height ( ) to be reconciled with magnetic field measurements at the Sun via potential field extrapolation (PFSS). However, during PSP ’s second encounter, the situation went back to a more classic SS height ( ). Here we use high-resolution observations of the photospheric magnetic field ( Solar Dynamics Observatory /Helioseismic and Magnetic Imager) to calculate neutral lines and boundaries of the open field regions for SS heights from 1.2 to 2.5 R ⊙ using an evolving PFSS model and the measured solar wind speed to trace the source of the wind observed by PSP to the low corona and photosphere. We adjust R SS to get the best match for the field polarity over the period 2018 October–November and 2019 March–April, finding that the best fit for the observed magnetic field polarity inversions requires a nonspherical SS. The geometry of the coronal hole boundaries for different R SS is tested using the PSP perihelion passes, 3D PFSS models, and LASCO/C2 observations. We investigate the sources of stronger-than-average magnetic fields and times of Alfvénic fast and slow wind. Only some of the strongly Alfvénic slow wind streams seen by PSP survive and are observed at 1 au: the origins and peculiar topology of the background in which they propagate is discussed.