Source-dependent properties of different slow solar wind states
Two distinct plasma states of slow solar wind are identified from in-situ measurements of the local magnetic field and the solar wind plasma by Parker Solar Probe (PSP) during Encounter 2. So close to the Sun the wind measured at PSP has not yet undergone too many transformations related to the expansion and propagation of the wind in the heliosphere and we focus on the wind intervals with no magnetic switchbacks. The two states differ by plasma beta, mass flux and magnetic pressure. A detailed
... ressure. A detailed study of the spacecraft connectivity, combined with the optimised PFSS-reconstructed solar magnetic field (from magnetic field maps and EUV observations of coronal holes), revealed that the boundary between the two states can be interpreted as a transition from a streamer-like to an equatorial coronal hole plasma flow. The streamer type tube has an expansion factor 20 times higher than the equatorial coronal hole tube, and a stronger expansion over a larger spatial extent. The simulations reproduce the properties observed in the data: slower and denser wind at the edge of the streamer compared to equatorial coronal hole plasma. Temperature profiles from simulations provide an explanation: due to the difference of photospheric magnetic field and different flux tube geometries, heating is more intense and lower along a streamer-like tube than along a coronal hole-like tube, even if footpoints of both tubes are very close to each other on the solar surface. This results in plasma outflows with different background properties at the edge of the streamer and at the boundary of the equatorial coronal hole, independently of the solar wind variability.