Nonequilibrium Ionization Effects on Coronal Plasma Diagnostics and Elemental Abundance Measurements

Abstract

Plasma diagnostics and elemental abundance measurements are crucial to help us understand the formation and dynamics of the solar wind. Here we use a theoretical solar wind model to study the effect of nonequilibrium ionization (NEI) on plasma diagnostic techniques applied to line intensities emitted by the fast solar wind. We find that NEI almost always changes the spectral line intensities with up to 120% difference for the lighter elements and for higher charge states of Fe even below 1.5 solar radii (R s ). The measured plasma density, temperature, and differential emission measure are only slightly affected by NEI. However, NEI significantly affects the first-ionization potential (FIP) bias and abundance ratio measurements, producing an error of up to a factor 4 at 1.5 R s for the Mg-to-Ne, Fe-to-S, and Ar-to-Fe ratios when EI is assumed. We conclude that it is very important to consider the NEI effect when spectral line intensities are synthesized and the FIP bias and elemental abundance are measured.

AWSoM Magnetohydrodynamic Simulation of a Solar Active Region. II. Statistical Analysis of Alfvén Wave Dissipation and Reflection, Scaling Laws, and Energy Budget on Coronal Loops

“…Finally, the inverted DEM for the observation requires further discussion as the inversion is an ill-posed problem with various limitations (see, e.g., Aschwanden et al 2015). In Shi et al (2019), we compared three methods and found that the MCMC method, although computationally expensive, can usually achieve a robust and accurate result. However, because the resulting DEM at a certain pixel is only the most probable curve among a batch of Monte Carlo realizations, the inversion result may still have a smooth falloff at high temperatures, even with a plasma temperature cutoff.…”

“…Interested readers are referred to a review by Aschwanden et al (2015) for more discussions and comparisons of some of the most used inversion methods. In Shi et al (2019), we found that the Markov Chain Monte Carlo (MCMC) method (Kashyap & Drake 1998) generally provides reasonable results. A Markov chain is a stochastic model that defines the transition from one state to the next using a probabilistic approach, and the MCMC method uses an ensemble of such chains to asymptotically determine the best solution, which is usually very robust.…”

Nonequilibrium Ionization Effects on Synthetic Spectra in the AWSoM Solar Corona

“…Such effects have direct consequences for diagnostic techniques making use of absolute line intensities or intensity ratios of lines from different ions, such as elemental abundances, plasma thermal distribution, and electron temperature, and can also affect the plasma radiative losses (Landi et al 2012b). It is therefore important to use the nonequilibrium ionization (NEI) assumption in coronal plasma diagnostics, see, e.g., Lee et al (2019), Shi et al (2019), andGilly &Cranmer (2020). Reviews about NEI effects on spectra in the solar atmosphere can be found in, e.g., Bradshaw & Raymond (2013) and Dudík et al (2017).…”

Spectral Imager of the Solar Atmosphere: The First Extreme-Ultraviolet Solar Integral Field Spectrograph Using Slicers

“…This transient ionisation in turn can affect other diagnostics, e.g., Refs. [87][88][89]. For a review of transient ionisation conditions, see Ref.…”