Solar wind kinetic exospheric models with typical coronal holes exobase conditions

Abstract

In coronal holes where densities are lower than in equatorial streamers, the exobase, which is the radial distance where collisions between solar wind particles become negligible, is located closer to the basis of the corona where the downward gravitationnal force exceeds the upward electrostatic force acting on the protons. Therefore, the total potential of the protons is a non‐monotonic function of the radial distance with a maximum value at a distance rmax. A new kinetic model with an exobase located at low radial distances is presented and compared to previous kinetic models where the exobase was located at larger radial distance. With such a low exobase, the electric field that ensures the quasi‐neutrality of the plasma is strongly enhanced which has for consequence to accelerate the solar wind to values comparable to the velocities observed in the fast solar wind. We show that the lower the radial distance of the exobase, the larger the bulk velocity of the solar wind at large distance.