Collisions, magnetization, and transport coefficients in the lower solar atmosphere

TL;DR

This paper provides detailed quantitative data on collision frequencies, magnetization, viscosity, and thermal conductivity in the lower solar atmosphere, essential for realistic modeling of solar phenomena.

Contribution

It offers the first comprehensive altitude-dependent dataset for collision and transport parameters, clarifying the physics of charged and neutral species interactions in the lower solar atmosphere.

Findings

Protons are unmagnetized in a layer at least 1000 km thick.

Viscosity and thermal conductivity are calculated for unmagnetized ion layers.

Regions of dominance for different collision types are identified.

Abstract

The lower solar atmosphere is an intrinsically multi-component and collisional environment with electron and proton collision frequencies in the range $10^{8}-10^{10}$ Hz, which may be considerably higher than the gyro-frequencies for both species. We aim to provide a reliable quantitative set of data for collision frequencies, magnetization, viscosity, and thermal conductivity for the most important species in the lower solar atmosphere. Having such data at hand is essential for any modeling that is aimed at describing realistic properties of the considered environment. We describe the altitude dependence of the parameters and the different physics of collisions between charged species, and between charged and neutrals species. Regions of dominance of each type of collisions are clearly identified. We determine the layers within which either electrons or ions or both are unmagnetized. Protons are shown to be un-magnetized in the lower atmosphere in a layer that is at least 1000 km thick even for a kilo-Gauss magnetic field that decreases exponentially with altitude. In these layers the dynamics of charged species cannot be affected by the magnetic field, and this fact is used in our modeling. Viscosity and thermal conductivity coefficients are calculated for layers where ions are unmagnetized. We compare viscosity and friction and determine the regions of dominance of each of the phenomena. We provide the most reliable quantitative values for most important parameters in the lower solar atmosphere to be used in analytical modeling and numerical simulations of various phenomena such as waves, transport and magnetization of particles, and the triggering mechanism of coronal mass ejections.