Application of a multi-species NLTE modeling framework to impulsive coronal heating and interpreting emission spectra.

Conventional approaches to constructing numerical models of the solar atmosphere assume a fully equilibrated plasma, wherein all species are in collisional thermal equilbrium amongst themselves and each other. This yields single fluid formulations of the governing evolution equations, such as ideal MHD, or, at best, a treatment that accomodates different electron and ionized hydrogen and helium temperatures. In reality, a comparison between the timescales of observed solar activity and inter-species collisional timescales demonstrates that the former can be significantly shorter than the latter. There are important consequences for the model predicted spectra that are frequently used to deduce the presence of physical processes from observed spectral signatures. For example, the true thermal width of an emission line can be very different to the width predicted by setting the ion temperature equal to the electron temperature (or to the formation temperature of the ion in equilibrium), leading to very misleading interpretations concerning the preferential energization of particular species and the presence of excess broadening due to (e.g.) turbulence.We will present a new multi-species modeling framework to accommodate the NLTE coupling between arbitrary species, including the strongly charged ion populations of relevance to the solar atmosphere, and some recent results from its application to impulsive coronal heating.