Parametric decay of a kinked Alfvén wave packet: 3D MHD Simulations*

Localized inversions of the magnetic field, known as switchbacks, are a common but little-understood phenomenon in the solar wind. In particular, their origin(s), evolution, and stability in the solar wind is yet to be determined. Simulations modeling switchbacks have previously investigated their stability in 2D. Here, we investigate the decay rate of a large-amplitude, broadband, localized Alfvénic wave-packet propagating obliquely to a uniform background magnetic field via MHD simulations in 3D. We show that the initial wave packet is unstable, and the decay is dominated by the parametric instability that develops in the plane of the wave packet. Transverse modes also grow when noise is added along the out-of-plane direction, which increases the decay rate of the wave. We investigate the effects of system size, aspect ratio, and propagation angle on the decay rate, and discuss the implications for lifetime-estimates of switchbacks in the solar wind and discuss their possible contribution to heating and turbulence onset.