Magnetic, kinetic, and transition regime: spatially segregated structure of compressive MHD turbulence

ABSTRACT Turbulence is a complex physical process prevalent in modern physics, particularly in ionized environments like interstellar gas, where magnetic fields play a dynamic role. However, the precise influence of magnetic fields in such settings remains unclear. We employ the Alfvén Mach number, ${\cal M}_{\rm A} = \sqrt{E_{\rm k}/E_B}$, to gauge the magnetic field’s significance relative to turbulent motion, uncovering diverse interaction patterns. In the low-${\cal M}_{\rm A}$ magnetic regime, the field is force-free, yet gas motion does not align with it. At intermediate ${\cal M}_{\rm A}$ (magnetic-kinetic transition regime), velocity and magnetic fields show peak alignment, likely due to rapid relaxation. In the high-${\cal M}_{\rm A}$ kinetic regime, both fields are irregular and unaligned. These regimes find observational counterparts in interstellar gas, highlighting the multifaceted nature of MHD turbulence and aiding future astrophysical interpretations.