Partially Ionized Solar Atmosphere: Two-fluid Waves and Their Cutoffs

A novel model of the solar atmosphere that accounts for partially ionized plasma is developed and used to study the propagation of magnetoacoustic-gravity waves, which are generated by solar granulation. The model includes neutrals in otherwise ionized plasma and therefore the considered waves are two-fluid waves. Numerical simulations of these waves allow computing their cutoff period and its variations in the solar atmosphere. The results of these computations are compared to the observational data collected by Wisniewska et al. and Kayshap et al., and a good agreement between the theory and observations is obtained. This first theoretical confirmation of the observational data profoundly shows the importance of effects caused by partially ionized plasma on the behavior of waves in the solar atmosphere, and on the origin of solar chromospheric oscillations. It is also suggested that theoretically predicted differences between the behavior of ions and neutrals can be verified by some currently operating solar missions.