Effects of Flow on Structure and Abundances in Multispecies Solar Coronal Loops

Abstract

We investigate the effects of large-scale bulk flows on coronal abundances using a multispecies numerical model. The model assumes that electrons, protons, and helium are in thermal equilibrium and constitute the bulk of the coronal plasma. Thermal diffusion and Coulomb friction are included. Temperature profiles for the bulk component and for each ion species are assumed, so the model reduces to a solution of mass and force balance for each component. We further assume that the bulk component has an upward bulk velocity at the base, and that ion flow speeds along field lines are negligible relative to the bulk flow. Coulomb coupling of the electrons and ions induces drag that counteracts the tendency of the ions to gravitationally settle. In regions of small ∇T, such as the outer regions of the corona, Coulomb drag is the only significant force counteracting gravitational settling in this model. We find that relatively modest bulk flows of tens of km s-1 can enhance ion abundances by 2-3 orders of magnitude over their values in low- or no-flow cases.