Modulational instability of finite-amplitude, circularly polarized Alfven waves

Journal Article · Fri Sep 15 04:00:00 EDT 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156451· OSTI ID:6879212

Derby, Jr, N F

The simple theory of the decay instability of Alfven waves is strictly applicable only to a small-amplitude parent wave in a low ..beta.. plasma, but, if the parent wave is circularly polarized, it is possible to analyze the situation without either of these restrictions. Results show that a large-amplitude circularly polarized wave is unstable with respect to decay into three waves, one longitudinal and one transverse wave propagating parallel to the parent wave and one transverse wave propagating antiparallel. The transverse decay products appear at frequencies which are the sum and difference of the frequencies of the parent wave and the longitudinal wave. The decay products are not familiar MHD modes except in the limit of small B and small amplitude and a backward-propagating circularly polarized wave. In this limit the other transverse wave disappears. The effect of finite ..beta.. is to reduce the linear growth rate of the instability from the value suggested by the simple theory. Possible applications of these results to the theory of the solar wind are briefly touched upon.

• Research Organization: Center for Space Research, Massachusetts Institute of Technology
• OSTI ID: 6879212
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 224:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALFVEN WAVES
AMPLITUDES
DECAY INSTABILITY
EQUATIONS
EQUATIONS OF STATE
FLUID MECHANICS
HYDRODYNAMICS
HYDROMAGNETIC WAVES
INSTABILITY
MAGNETOHYDRODYNAMICS
MECHANICS
PLASMA
PLASMA INSTABILITY
POLARIZATION
SOLAR ACTIVITY
SOLAR CORONA
SOLAR WIND
WAVE PROPAGATION