Magnetohydrodynamic waves in solar partially ionized plasmas: twofluid approach 

Teimuraz Zaqarashvili Submitted: 20110121 02:17
Partially ionized plasma is usually described by singlefluid approach, where the ionneutral collision effects are expressed by Cowling conductivity in the induction equation. However, the singlefluid approach is not valid for the timescales less than ionneutral collision time. For these timescales the twofluid description is better approximation. We derive the dynamics of magnetohydrodynamic waves in twofluid partially ionized plasmas and to compare the results with those obtained under singlefluid description. Twofluid magnetohydrodynamic equations are used, where ionelectron plasma and neutral particles are considered as separate fluids. Dispersion relations of linear magnetohydrodynamic waves are derived for simplest case of homogeneous medium. Frequencies and damping rates of waves are obtained for different parameters of background plasma. We found that two and singlefluid descriptions give similar results for low frequency waves. However, the dynamics of MHD waves in twofluid approach is significantly changed when the wave frequency becomes comparable or higher than ionneutral collision frequency. Alfvén and fast magnetoacoustic waves attain their maximum damping rate at particular frequencies (for example, the peak frequency equals 2.5 ionneutral collision frequency for 50 % of neutral Hydrogen) in wave spectrum. The damping rates are reduced for higher frequency waves. The new mode of slow magnetoacoustic wave appears for higher frequency branch, which is connected to neutral hydrogen fluid. The singlefluid approach perfectly deals with slow processes in partially ionized plasmas, but fails for timescales smaller than ionneutral collision time. Therefore, twofluid approximation should be used for the description of relatively fast processes. Some results of singlefluid description, for example the damping of highfrequency Alfvén waves in the solar chromosphere due to ionneutral collisions, should be revised in future.
Authors: Zaqarashvili, T. V., Khodachenko, M. K., Rucker, H. O.
Projects: None

Publication Status: A&A (accepted)
Last Modified: 20110121 08:46


