Diagnostics of Kappa Distributions from Optically Thin Solar Spectra

We review the diagnostics of the non-Maxwellian Kappa distributions from the remote-sensing spectroscopic observations of the optically thin parts of the solar atmosphere. While the electron distributions are typically diagnosed from ratios of emission line intensities alongside other plasma parameters such as electron densities and temperature, the ion distributions affect the shape of the line profiles and are more readily seen. The electron Kappa distributions relies on accurate calculations of synthetic spectra which in turn depend on evaluation of the ionization, recombination, and collisional excitation rates. Even though the observational uncertainties can be significant, recent results point out to a possibly widespread presence of low κ-values, typically κ = 2, in many regions of the solar atmosphere, including the transition region, active region corona, and solar flares, especially the reconnection region.