Quasi-two-dimensionality of three-dimensional, magnetically dominated, decaying turbulence

Decaying magnetohydrodynamic (MHD) turbulence plays a crucial role in various astrophysical contexts, including early universe magnetic fields, star formation, galaxy cluster turbulence, magnetospheres, and the solar corona. While previous studies have highlighted the role of magnetic reconnection in the nonhelical case of magnetically dominated turbulence, we show that it remains crucial even in the fully helical case and likely drives the inverse energy transfer. Additionally, we find a similarity in power-law decay exponents between 2.5D and 3D simulations. To investigate this, we explore the quasi-two-dimensionalization of the 3D system using Minkowski functional analysis, which reveals significant local anisotropies in magnetic structures. We further propose a quasi-two-dimensional hierarchical merger model that successfully reproduces the observed power-law scalings. In the nonhelical case, we demonstrate that helicity-based constraints are insufficient, and anastrophy (vector potential squared) remains the most relevant invariant, aligning with the system's quasi-two-dimensional nature.