Maile Marriott Thesis Defense

Abstract: The solar wind provides a natural laboratory for investigating plasma turbulence and magnetic structures, including a type of Alfv\'enic fluctuation called switchbacks—localized reversals in the magnetic field. In this thesis, their decay via the parametric decay instability (PDI) is investigated to constrain their origins and their potential contributions to heating and turbulence. I have focused on three types of models: 1D arc-polarized waves, 2.5D switchback-like kinked wavepackets, and fully 3D arc-polarized waves. Through a combination of linear analysis, analytical modeling, and novel numerical techniques, this thesis advances our understanding of the parametric decay instability (PDI) and its role in shaping the lifetime, origin, and energetic contribution of switchback-like structures in the solar wind. By systematically exploring the effects of wave geometry, boundary conditions, and solar wind expansion, the research clarifies theoretical constraints on switchback (and Alfv\'en waves in general) stability and decay processes. It also lays the groundwork for future studies of PDI in solar wind conditions, particularly for fully 3D arc-polarized waves.