Constraints on ion outflow speeds and electron distribution function in the corona derived from sumer electron temperatures and SWICS ion fractions Original Research Article

It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in the in situ solar wind. In the present paper we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner corona: 1) the electron distribution function has to be Maxwellian or close to Maxwellian close to the coronal base; 2) the non-Maxwellian character of the distribution has to develop rapidly as a function of height and has to reach close to interplanetary properties inside of a few solar radii; 3) ions of different elements have to flow with significantly different speeds to separate their “freezing-in” distances sufficiently so they can encounter different distribution functions. We chose a set of observationally constrained coronal plasma parameters to demonstrate that these conditions are general requirements if both coronal electron temperatures and in situ ion fractions are correct. However, the details of the required distribution functions are very sensitive to the exact electron temperature, density and ion flow speed profiles in the region of the corona where the ions predominantly form.