An indication of the existence of a solar wind strahl at 10 AU

Authors

  • A. P. Walsh,

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    2. Now at Science and Robotic Exploration Directorate, ESA/ESTEC, Noordwijk, The Netherlands
    Search for more papers by this author
  • C. S. Arridge,

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    2. The Centre for Planetary Sciences at UCL/Birkbeck, London, UK
    Search for more papers by this author
  • A. Masters,

    1. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
    Search for more papers by this author
  • G. R. Lewis,

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    2. The Centre for Planetary Sciences at UCL/Birkbeck, London, UK
    Search for more papers by this author
  • A. N. Fazakerley,

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    Search for more papers by this author
  • G. H. Jones,

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    2. The Centre for Planetary Sciences at UCL/Birkbeck, London, UK
    Search for more papers by this author
  • C. J. Owen,

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    Search for more papers by this author
  • A. J. Coates

    1. Department of Space and Climate Physics, University College London, Mullard Space Science Laboratory, Holmbury St. Mary, UK
    2. The Centre for Planetary Sciences at UCL/Birkbeck, London, UK
    Search for more papers by this author

Corresponding author: A. P. Walsh, Science and Robotic Exploration Directorate, ESA/ESTEC, Noordwijk, Netherlands. (awalsh@rssd.esa.int)

Abstract

[1] The solar wind electron distribution is observed near and within 1 AU to consist of three components: a thermal core, a suprathermal halo, and a suprathermal strahl. The former two components are isotropic, while the strahl is field aligned and flows outward along the interplanetary magnetic field. The evolution of solar wind electrons with heliocentric distance is poorly understood; although the halo is thought to be formed through pitch angle (PA) scattering of the strahl, the responsible physical process has not been conclusively identified. Measurements of solar wind electrons throughout the heliosphere are required to solve this problem. We present the first observations of the suprathermal components of the solar wind electron distribution made outside 5 AU. We find indications of a strahl component narrower than that predicted by extrapolating observations and models of electrons in the inner heliosphere, suggesting the rate of electron pitch angle scattering in the solar wind can decrease with increasing heliocentric distance.

Ancillary