Large amplitude Alfvénic fluctuations, sometimes leading to localized inversions of the magnetic field, called switchbacks, are a common but poorly understood phenomenon in the solar wind. In particular, their origin(s), evolution, and stability within solar wind conditions are yet to be fully understood. Simulations modeling switchbacks have previously studied their stability in 2D. Here, we investigate the decay process of Alfvén wave packets via MHD simulations in 3D by characterizing the effects of system size, aspect ratio, and propagation angle on the decay rate. We show that the initial wave packet is unstable to parametric instabilities that develop compressible and Alfvénic secondary modes in the plane of, and transverse to, the initial wave packet propagation direction. The growth of transverse modes, absent in 2D simulations, increases the decay rate of the wave packet. We finally discuss the implications of our results for lifetime estimates of switchbacks and wave energy conversion in the solar wind.

中文翻译：

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扭结阿尔文波包的参数衰减：3D 磁流体动力学模拟


大幅度的阿尔芬涨落有时会导致磁场局部反转（称为之字形），这是太阳风中常见但人们知之甚少的现象。特别是，它们的起源、演化和在太阳风条件下的稳定性尚未完全了解。之字形的模拟建模之前已经研究了其二维稳定性。在这里，我们通过 3D MHD 模拟研究阿尔文波包的衰减过程，通过表征系统尺寸、纵横比和传播角度对衰减率的影响。我们表明，初始波包对于参数不稳定性是不稳定的，参数不稳定性会在初始波包传播方向的平面和横向上产生可压缩和阿尔芬二次模式。二维模拟中不存在的横向模式的增长会增加波包的衰减率。最后，我们讨论了我们的结果对太阳风中之字形和波浪能转换的寿命估计的影响。