关于空间等离子体中非线性Alfven共振的有效性
On the validity of nonlinear Alfven resonance in space plasmas
摘要：
在线性耗散磁流体动力学（MHD）近似下，当磁流体波的频率等于磁表面的局部Alfven（或慢）频率时，高雷诺数磁等离子体中的磁流体动力学（MHD）波将表现出近共振特性。这种接近共振的行为被限制在一个薄的区域，称为耗散层，它包含了共振磁表面。虽然驱动磁流体动力学波在远离共振表面处具有小的无量纲振幅，但耗散层中的这种近共振行为可能导致线性理论的崩溃。我们的目的是研究阿尔芬耗散层中的非线性效应。本文用非线性慢共振波的简化匹配渐近展开法来描述Alfven耗散层中的非线性效应。导出了Alfven耗散层中共振波的非线性修正，证明了在Alfven共振（各向同性/各向异性耗散）下，波动力学可以用线性理论精确地描述。
英文摘要：
In the approximation of linear dissipative magnetohydrodynamics (MHD) it can be shown that driven MHD waves in magnetic plasmas with high Reynolds number exhibit a near resonant behaviour if the frequency of the wave becomes equal to the local Alfven (or slow) frequency of a magnetic surface. This near resonant behaviour is confined to a thin region, known as the dissipative layer, which embraces the resonant magnetic surface. Although driven MHD waves have small dimensionless amplitude far away from the resonant surface, this near-resonant behaviour in the dissipative layer may cause a breakdown of linear theory. Our aim is to study the nonlinear effects in the Alfven dissipative layer. In the present paper, the method of simplified matched asymptotic expansions developed for nonlinear slow resonant waves is used to describe nonlinear effects inside the Alfven dissipative layer. The nonlinear corrections to resonant waves in the Alfven dissipative layer are derived and it is proved that at the Alfven resonance (with isotropic/anisotropic dissipation) wave dynamics can be described by the linear theory with great accuracy.
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