Wave modes in magnetic elements in a stratified atmosphere

Abstract

view Abstract Citations (9) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Wave modes in magnetic elements in a stratified atmosphere. Wilson, P. R. Abstract The vibration modes of a magnetic flux element embedded in a compressible, gravitationally stratified atmosphere are considered. A local dispersion relation is first derived for a force-free field which decreases exponentially with height, and this is applied to a magnetic flux sheath lying within the local region. The sheath is embedded in an isothermal, gravitationally stratified plasma for which the standard dispersion relation applies globally. The velocity and pressure balance conditions across the interface restrict the possible vibration modes of the system. For the pulsation or varicose mode, a modified acoustic mode and a modified fast mode are obtained. The latter has a cutoff frequency which is greater than the acoustic cutoff and suggests that waves of shorter periods may occur in the presence of magnetic elements. For the sinuous or taut wire mode, complex solutions for the dispersion equation are obtained. For one of these the real part is large and negative, indicating that, within the limitations of a linear analysis, waves propagate with increasing amplitude. The possible significance of this is briefly discussed. Publication: The Astrophysical Journal Pub Date: November 1978 DOI: 10.1086/156573 Bibcode: 1978ApJ...225.1058W Keywords: Magnetohydrodynamic Waves; Plasma Waves; Stellar Magnetic Fields; Wave Propagation; Atmospheric Models; Boundary Value Problems; Perturbation Theory; Propagation Modes; Solar Magnetic Field; Geophysics; Alfven Waves:Solar Magnetic Fields; Hydromagnetics full text sources ADS |