A COLLISIONAL KINETIC-MODEL OF THE POLAR WIND

The effects of Coulomb collisions in the transition region between the collision-dominated regime at low altitudes and the collisionless reg ime at high altitudes have been taken into account to study the escape of H+ ions through a background of O+ ions. The H+ ion velocity distr ibution function is determined as a function of altitude for realistic initial conditions in the whole velocity space. We emphasize the impo rtance for a correct choice of the boundary conditions at v=0 to obtai n regular mathematical solutions. The results of this kinetic model ar e compared with results of earlier polarwind models based on different approximations of the plasma transport equations.