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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 34, issue 12
Ann. Geophys., 34, 1175–1189, 2016
https://doi.org/10.5194/angeo-34-1175-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 34, 1175–1189, 2016
https://doi.org/10.5194/angeo-34-1175-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 15 Dec 2016

Regular paper | 15 Dec 2016

Observations of diffusion in the electron halo and strahl

Chris Gurgiolo1 and Melvyn L. Goldstein2 Chris Gurgiolo and Melvyn L. Goldstein
  • 1Bitterroot Basic Research, Hamilton, Montana, USA
  • 2Heliospheric Physics Laboratory, Code 672, NASA Goddard Space Flight Center, Greenbelt, MD, USA

Abstract. Observations of the three-dimensional solar wind electron velocity distribution functions (VDF) using ϕθ plots often show a tongue of electrons that begins at the strahl and stretches toward a new population of electrons, termed the proto-halo, that exists near the projection of the magnetic field opposite that associated with the strahl. The energy range in which the tongue and proto-halo are observed forms a “diffusion zone”. The tongue first appears in energy generally near the lower-energy range of the strahl and in the absence of any clear core/halo signature. While the ϕθ plots give the appearance that the tongue and proto-halo are derived from the strahl, a close examination of their density suggests that their source is probably the upper-energy core/halo electrons which have been scattered by one or more processes into these populations.

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Using Cluster data we have noted observations of diffusion-like signatures in the energy range where the the solar wind halo and strahl populations overlap. This includes the development of a proto-halo. At present the source of this diffusion is not known or understood. The prime analysis was carried out through the use of phi–theta plots at individual energy steps. The motivation was to understand if repartitioning in energy was occurring at these locations.
Using Cluster data we have noted observations of diffusion-like signatures in the energy range...
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