On the exospheric approach for the solar wind acceleration

We present the basics of the exospheric models of the solar wind accelerati on. In these models the plasma is assumed fully collisionless above a typic al altitude in the corona. The solar wind is accelerated by the interplanet ary electrostatic potential which is needed to warrant the equality of the proton and electron fluxes. These models suggest that the fast wind emanati ng from the polar regions could be due to the presence of non-thermal elect ron distributions in the corona.