Sun and Solar Wind

Ulysses, Solar Wind
SWOOPS observations of the solar wind during Ulysses' first full polar orbit around the Sun. Credit: McComas, D. J., et al. (2000), J. Geophys. Res., 105, 10,419-10,433.

The Sun’s corona contains hot plasma, much hotter than the surface of the Sun, called the solar wind. The solar wind consists mostly of protons, electrons, and some alpha particles. Observations show that the solar wind emitted at low latitudes near the ecliptic plane travels at ~300-500 km s-1, with significant variability in speed, density, and temperature over small time-scales. At higher latitudes, the solar wind is emitted from large polar coronal holes, regions of open magnetic field lines, at faster speeds (~700-800 km s-1). As the solar wind propagates away from the Sun, it is supplied with pickup ions created by the ionization of interstellar neutral atoms. The Sun also emits disturbances such as solar flares and coronal mass ejections, which propagate into the interplanetary medium. Energetic particles are accelerated by these disturbances, as well as by shock waves created by fast-slow solar wind stream interactions.

Relevant Observations:

  • Energetic particles as close as 9 solar radii from the Sun (ISʘIS)
  • Solar wind protons, electrons, and alphas at 1 au (SWEPAM)
  • Solar wind ions and electrons out to ~5 au at high latitudes (SWOOPS)
  • Solar wind protons, alphas, and pickup ions out to ~40 au (SWAP)

Examples of Research Topics:

  • Acceleration and transport of energetic particles from the Sun
  • Interstellar pickup ions at interplanetary shocks
  • Radial and temporal evolution of the bulk solar wind properties