Reconciling Spectroscopic Electron Temperature Measurements in the Solar Corona with In Situ Charge State Observations

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Abstract
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 situ in the solar wind. In the present Letter, 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 at 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, and (3) ions of different elements have to flow with significantly different speeds to separate their "freezing-in" distances sufficiently so that they can encounter different distribution functions. We choose two examples to demonstrate that these conditions are general requirements if both coronal electron temperatures and in situ ion fractions are correct. However, these two examples also show that 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.