1Bitterroot Basic Research, Hamilton, Montana, USA
2Heliospheric Physics Laboratory, Code 672, NASA Goddard Space Flight
Center, Greenbelt, MD, USA
Received: 16 Jun 2016 – Revised: 24 Oct 2016 – Accepted: 09 Nov 2016 – Published: 15 Dec 2016
Abstract. Observations of the three-dimensional solar wind electron velocity distribution functions (VDF) using ϕ–θ 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 ϕ–θ 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.
Gurgiolo, C. and Goldstein, M. L.: Observations of diffusion in the electron halo and strahl, Ann. Geophys., 34, 1175-1189, doi:10.5194/angeo-34-1175-2016, 2016.