Resonance absorption of compressible magnetohydrodynamic waves at thin surfaces

Journal Article · Wed Jun 01 04:00:00 EDT 1988 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA093iA06p05423· OSTI ID:5184030

Hollweg, J V; Yang, G ^[1]

---

1. Univ. of New Hampshire, Durham (USA)

If an MHD surface wave is supported by a true discontinuity, then the total pressure fluctuation, {delta}P{sub tot}, is constant across the discontinuity. If the discontinuity is replaced by a thin transition layer, then {delta}P{sub tot}, will be approximately constant across the transition layer, with a value approximately the same as the value obtained for the case of a true discontinuity. We use this approximation to study the behavior of the plasma and fields in the transition layer. The authors regard {delta}P{sub tot} as known, and write the relevant equations in forms in which {delta}P{sub tot} appears as driving terms. Two resonances appear. The cusp resonance affects the density and pressure fluctuations, and the velocity and magnetic field components along the background magnetic field, B{sub o}. The Alfven resonance affects the velocity and magnetic field components normal to B{sub o}. They concentrate on the Alfven resonance, and show in a simple way how energy is pumped out of the surface wave into thin layers surrounding the resonant field lines. They consider also the effects of three types of viscosity on the Alfven resonance. Only classical shear viscosity is able to absorb the energy which is pumped into the thin resonant layer. In the steady state, the net viscous heating is independent of the viscosity coefficient, if the heating occurs in a sufficiently thin layer. They suggest that the large velocity shears which occur in the vicinity of the resonant field lines can lead to Kelvin-Helmholtz instabilities, which can in turn lead to an effective eddy viscosity, which they estimate to be large enough in the solar corona to distribute heat throughout large portions of coronal active region loops. They show also that coronal heating by the Alfven resonance is compatible with a variety of coronal data.

• OSTI ID: 5184030
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 93:A6; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
ENERGY TRANSFER
FLUID FLOW
HEAT TRANSFER
HEATING
HELMHOLTZ INSTABILITY
HYDROMAGNETIC WAVES
INCOMPRESSIBLE FLOW
INSTABILITY
PLASMA INSTABILITY
PLASMA MACROINSTABILITIES
PRESSURE GRADIENTS
SHEAR
SOLAR ATMOSPHERE
SOLAR CORONA
STEADY-STATE CONDITIONS
STELLAR ATMOSPHERES
STELLAR CORONAE
VISCOSITY
WAVE PROPAGATION