On the velocity drift between ions in the solar atmosphere

Abstract:

Very recent results that compare ALMA and IRIS observations with 2D radiative MHD including non-equilibrium ionization and ambipolar diffusion models of the type II spicules reveal that these models may underestimate the energy dissipated in the chromosphere. The solar atmosphere is composed of many species that are populated at different ionization and excitation levels. The upper chromosphere, transition region, and corona are nearly collisionless. Consequently, slippage between, for instance, ions and neutral particles, or interactions between separate species, may play an important role in the local momentum and energy balance. The interaction between species is missing in the 2D radiative MHD model. We have developed a 3D multi-fluid and multi-species numerical code (Ebysus) to investigate such effects. Ebysus is capable of treating species (e.g., hydrogen, helium, etc) and fluids (neutrals, excited and ionized elements) separately. Treating different species as different fluids leads to drifts between different ions and an electric field that couple these motions. Different ionized species and momentum exchange can dissipate this velocity drift, i.e., convert wave kinetic energy into thermal energy. High-frequency Alfven waves, driven for instance by reconnection, thought to occur in the solar atmosphere, can drive such multi-ion velocity drifts.