The solar wind observed over the first orbits by Parker Solar Probe : new insights into the origin of the heliosphere

Since the launch of Parker Solar Probe (PSP) in 2018, a new window has opened into understanding the inner heliosphere.The first Probe encounters, with a perihelion at 35.6 Solar Radii (Rs) from Sun-center illustrated the complexity of the mapping of the magnetic field at the Sun even into the inner heliosphere. In Encounter (E) 1, Probe connected to a small, overexpanding coronal hole, and the resulting slow solar wind flow was dominated by highly Alfvénic fluctuations, including local radial magnetic field inversions called switchbacks. Recent Encounters E4 and E5, with perihelia at a distance of 27.8 Rs, show the importance of the mixing of spatial and intrinsically time-dependent behavior. Here we describe the general features of the solar wind seen by PSP in orbits 4 and 5, with specific emphasis on the polarity of the field, the properties of the fluctuations observed, and their association with the regions of origin of the wind and with intrinsically time-dependent processes at the source. We use the Potential Field Source-Surface (PFSS) model of De Rosa and Schrijver, based on SDO/HMI magnetogram data in conjunction photospheric transport, to extrapolate the field from the solar surface out to an appropriate source surface, and then images from STEREO, LASCO and SDO/AIA to compare the results with the magnetic field and plasma seen by Probe. In situ measurements are then used to compute plasma and turbulence properties, such as Alfvénicity, and determine the nature of the discontinuities separating different types of solar wind flows in situ. Probe in E4 and E5 remained very close to the heliospheric current sheet, and traversed structures such as pseudostreamer stalks as well as the heliospheric current sheet itself. It observed both strongly Alfvénic wind and wind with less clear Alfvénic character. When compared to the first encounter, the solar wind conditions seen by Probe at the most recent E4 and E5 is more typical of the wind seen in the ecliptic in periods of increasing solar activity. Switchbacks are confirmed to be an intrinsic feature of the nascent solar wind everywhere except above helmet streamers. To conclude we will discuss how new PSP measurements change our views of heliospheric magnetic field expansion and solar wind acceleration.