Solar wind kinetic exospheric modelswith typical coronal holes exobase conditions

摘要

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