A collisional kinetic model of the polar wind

Abstract

The effects of Coulomb collisions in the transition region between the collision‐dominated regime at low altitudes and the collisionless regime at high altitudes have been taken into account to study the escape of H + ions in the polar wind. A specialized spectral method is used to solve the steady state Fokker‐Planck equation describing the diffusion and upward bulk motion of H + ions through a background of O + ions. The H + ion velocity distribution function is determined as a function of altitude for realistic initial conditions in the whole velocity space. We emphasize the importance for a correct choice of the boundary conditions at v = 0 to obtain regular mathematical solutions. The results of this kinetic model are compared with results of earlier polar wind models based on different approximations of the plasma transport equations.