# Alfvén Waves in Partially Ionised Solar Steady-State Plasmas

## TL;DR

This paper studies how Alfvén waves behave in solar plasmas with partial ionisation and steady particle flows.

## Contribution

The study introduces a two-fluid model to show how steady flows modify Alfvén wave properties in partially ionised solar plasmas.

## Key findings

- Steady flows cause Doppler shifts and propagation direction reversal in Alfvén waves.
- Flow-dependent damping rates and a new mode linked to neutral flow and collisions are identified.
- Conditions for flow-driven mode conversion are determined in partially ionised solar plasmas.

## Abstract

Our study investigates the properties of Alfvén waves in partially ionised solar plasmas in the presence of steady, field-aligned, flows of charged and neutral particles. Our work aims to understand how such flows modify wave propagation and damping in environments where ion-neutral collisions are significant. We employ a two-fluid model that treats ions and neutrals as separate colliding fluids and incorporates background steady flows for both species. Using a combination of analytical dispersion analysis and numerical solutions, we examine the impact of these flows on the behaviour of Alfvén waves. Our results show that steady flows lead to substantial modifications of wave properties, including Doppler shifts, propagation direction reversal, flow-dependent changes in damping rates, and the appearance of a new mode associated with neutral flow and collisional coupling. We also identify conditions under which flow-driven mode conversion can arise. Our results offer new insights into the interplay between plasma flows and particle collisions in the regions of the solar atmosphere where partial ionisation is relevant.