Characterizing thermal expansion profile of solar wind streams with Parker Solar Probe SWEAP and FIELDS

The Parker Solar Probe (PSP) is taking first-of-its kind measurements of the inner heliosphere, paving the way for a new understanding of processes that drive heating in the solar corona and beyond. In its first two orbits of the Sun, PSP reached as close as 0.17 AU (37 solar radii) from the Sun's center. At such close distances, instruments on PSP are uniquely suited to identifying discrete streams of fast solar wind thanks to minimal turbulent mixing between fast streams and any surrounding slow wind. Furthermore, at perihelion PSP's angular speed exceeds that of solar rotation, meaning that the probe is able to sample a given solar longitude over a radial range of as much as 20 solar radii. Taking advantage of these capabilities of PSP, we used data from its first two orbits taken by the Solar Wind Electrons Alphas and Protons (SWEAP) Solar Probe Cup as well as magnetic field data taken by the FIELDS suite to search for solar wind streams crossed by PSP at multiple points near perihelion. We then characterized the radial temperature profile of these streams to better understand the thermal behavior of the solar wind outside the solar corona. This work was supported by the NSF-REU solar physics program at SAO, grant number AGS-1560313.