Journal of Geophysical Research vol:104 issue:A8 pages:17021-17032
Typical electron velocity distribution functions observed at 1 AU from the Sun by the 3DP instrument onboard Wind are used as boundary conditions to determine the electron velocity distribution function at 4 solar radii in the corona. The velocity distribution functions (VDFs) at low altitude are obtained by solving the Fokker-Planck equation, using two different sets of boundary conditions. The first set typically corresponds to a VDF observed in a low-speed solar wind flow (i.e., characterized by "core" and "halo" electrons); the second one corresponds to highspeed solar wind (i.e., characterized by "core," "halo,", and "strahl" populations). We use the observed electron VDFs as test particles, which are submitted to external forces and Coulomb collisions with a background plasma. Closer to the Sun, the relative density of the core electrons is found to increase compared to the density of the halo population. Nevertheless, we find that in order to match the observed distributions at 1 AU, suprathermal tails have to be present in the VDF of the test electron at low altitudes in the corona.