Berlin 2005 – wissenschaftliches Programm
EP 3.6: Vortrag
Samstag, 5. März 2005, 11:00–11:15, TU BH349
Electron halo and strahl formation in the solar wind by resonant interaction with whistler waves — •Christian Vocks and Gottfried Mann — Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam
Observations of solar wind electron velocity distribution functions (VDFs) reveal considerable deviations from a simple Maxwellian VDF. A thermal core and a suprathermal halo and anti-sunward, magnetic field-aligned beam or “strahl” can be distinguished. A kinetic model of the electrons in the solar corona and wind is presented that includes resonant interaction between electrons and whistler waves. The resonance condition with anti-sunward propagating whistler waves can only be fulfilled by sunward moving electrons, and vice versa. Anti-sunward propagating whistlers can accelerate suprathermal electrons significantly in the solar corona. In interplanetary space, the escaping electrons lead to an enhancement of suprathermal electron fluxes above the core flux, in agreement with observations. But the magnetic mirror force focuses these electrons into an extremely narrow beam that is not confirmed observationally. Thus, a diffusion mechanism for anti-sunward moving electrons must exist. Sunward propagating whistler waves can provide this diffusion. Their wave power is estimated as a small fraction of the total wave power that is measured in interplanetary space. The kinetic results show that the whistler waves are capable of influencing the solar wind electron VDFs significantly, leading to the formation of both the halo and strahl populations, and a more isotropic distribution at higher energies, in good agreement with solar wind observations.