Parametric excitation of alfvén wave by magnetosonic wave with oblique propagation

Abstract

A parametric excitation of the Alfvén wave ( k A, ω a ) by the magnetosonic wave ( K 1 fs , ω 1 fs ), which propagates obliquely to the static magnetic field, has been analyzed. The theoretical model for a one-fluid with uniform, unbounded, ideally conducting and compressible plasma is employed. The resonance conditions are chosen such as, k 1 fs = k 1 fs + k A and ω 1 fs − ω A = δ ∼ ω 2 fs . The p wave is assumed to be strong enough, so that the pump wave is given as a constant. In both the case of the standing and the propagating pump the growth rates of the excited waves depend on not only the pump power but also the β-ratio. In the standing pump the threshold pump intensity of the oscillating instability is zero at the perfect matching. It is found that we can obtain a larger growth rate of the parametric excitation of Alfvén wave by the fast magnetosonic pump wave for θ 1f ∼ 70–80° and the occurrence regions of parametric excitations are localized at the resonance point in the magnetosphere ( β ∼ m e / m i ). It is concluded that the parametric instability of Pc3 range HM-waves is the more possible theory than the linear resonance theory.