Interpreting the Effects of Non-Equilibrium Ionization on Remote Sensing and In-Situ Observations Using Synthetic Data

The heavy ion charge states of the solar plasma carry information about the physical processes that occurred as plasma is released from the solar corona. While charge states are directly and routinely measured in the inner heliosphere, they are also fundamental components to spectral line formation. Therefore it is critical to fully understand the information they carry about coronal heating and solar wind formation and acceleration. Due to the sudden density drop in the solar atmosphere, the charge states freeze-in within a few solar radii in the inner corona. When plasma motions are fast, the heavy ions spend less time than it would take to reach ionization equilibrium, and therefore the plasma freezes in while being out of ionization equilibrium. In-situ observations directly measure heavy ions with non-equilibrium charge state distributions, but in case of remote-sensing observations - when studying the non-flaring solar corona - the usual assumption is that the plasma is in equilibrium. Because of the above discussion, such an approach is often quite inaccurate, even in the case of the quiet Sun.

In this study we use the latest Alfvén Wave Solar atmosphere Model of the Space Weather Modeling Framework (SWMF/AWSoM) to model the solar corona and inner heliosphere: along with the basic plasma properties we calculate non-equilibrium ionization of the plasma throughout the whole 3D domain and study how the initial plasma undergoes ionization while being pushed into the interplanetary space. We reproduce the plasma conditions observed in-situ at Solar Orbiter's trajectory and at Earth along with synthetic in-situ charge state observations of commonly studied ions. We also use the 3D non-equilibrium ionization results to calculate the emission of individual spectral lines and narrowband images and point out the signatures of non-equilibrium processes while comparing them to observations.