Coronal heating and solar wind acceleration; Gyrotropic electron-proton solar wind

In coronal holes the electron (proton) density is low, and heating of the p roton gas produces a rapidly increasing proton temperature in the inner cor ona. In models with a reasonable electron density in the upper transition r egion the proton gas becomes collisionless some 0.2 to 0.3 solar radii into the corona. In the collisionless region the proton heat flux is outwards, along the temperature gradient. The thermal coupling to electrons is weak i n coronal holes, so the heat flux into the transition region is too small t o supply the energy needed to heat the solar wind plasma to coronal tempera tures. Our model studies indicate that in models with proton heating the in ward heat conduction may be so inefficient that some of the energy flux mus t be deposited in the transition region to produce the proton fluxes that a re observed in the solar wind. If we allow for coronal electron heating, th e energy that is needed in the transition region to heat the solar wind to coronal temperatures, may be supplied by heat conduction from the corona.