The effect of wave—particle interactions on the polar wind: Preliminary results

Abstract

A Monte Carlo simulation was developed in order to study the effects of wave-particle interactions (WPI) on the plasma outflow in the polar wind. The simulation also considered the other mechanisms included in the ‘classical’ polar wind studies such as gravity, the polarization electrostatic field, and the divergence of geomagnetic field lines. Although the plasma consisted of electrons, H + and O + ions, we emphasized the behavior of H + in this preliminary study. The ion distribution function, as well as the profiles of its moments (density, drift velocity, temperatures, etc.) were found for different levels of WPI, that is, for different values of normalized diffusion rates in the velocity space ( D T(H +)). We found that as the WPI strength increases: (1) the ion drift velocity increases and its density decreases; (2) the perpendicular temperature T ⊥( H +) increases; (3) the parallel temperature T( H +) first decreases and then increases due to the balance between the parallel adiabatic cooling and the transfer of the energy from the perpendicular to the parallel direction; and (4) the temperature anisotropy ( T ∥( H +) T ⊥( H + ) )is reduced and even reversed in some cases. For strong WPI ( D ̃ ⊥( H +) ⪢ 1 ), the ion distribution function shows weak conic features at high altitudes.