Anomalous compressible mode generation by global frame projections of pure Alfven mode
arXiv:2301.13344 · doi:10.1093/mnras/stad287
Abstract
Alfven wave is the single most important physical phenomenon of magneto-hydrodynamic turbulence and has far-reaching impact to almost all studies related to astrophysical magnetic field. Yet the restoration of the Alfven wave fluctuations from a given magnetic field, aka the local Alfven wave problem, is never properly addressed in literature albeit its importance. Previous works model the Alfven wave fluctuation as the perturbation along a straight-line, constant magnetic field. However, Lazarian & Pogosyan (2012) suggested that the decomposition of Alfven wave along a straight line, aka. the global frame decomposition, has a factor of discrepancy to the true local Alfven wave fluctuation. Here we provide a geometric interpretation on how the local Alfven wave is related to the global frame through the use of vector frame formulation. We prove both analytically and numerically that the local frame Alfven wave is an orthogonal transformation of that of the global frame and related by the local Alfvenic Mach number. In other words, when we observe Alfven wave in the global frame of reference, some of the Alfven wave will be mistaken as compressible waves. The importance of frame choices have a far-reaching impact to the analytical studies of MHD turbulence. Combining the frame formalism and the new techniques we can have accurate measurement to some of the fundamental turbulence properties like the inclination angle of mean magnetic field relative to the line of sight.
18 pages, 12 figures, accepted by MNRAS for publication
References in corpus (16)
- Theory of Star Formation
- Compressible Turbulence in Galaxy Clusters: Physics and Stochastic Particle Re-acceleration
- Density Fluctuations in MHD Turbulence: Spectra, Intermittency and Topology
- Cosmic Ray Propagation: Nonlinear Diffusion Parallel and Perpendicular to Mean Magnetic Field
- The Power Spectrum of Supersonic Turbulence in Perseus
- Tracing interstellar magnetic field using velocity gradient technique: Application to Atomic Hydrogen data
- Damping of Alfven waves by Turbulence and its Consequences: from Cosmic-Rays Streaming to Launching Winds
- Studying Turbulence from Doppler-broadened Absorption Lines: Statistics of Logarithms of Intensity
- Power spectrum of HI intensity fluctuations in DDO 210
- Study of velocity centroids based on the theory of fluctuations in position-position-velocity space
- Technique for separating velocity and density contributions in spectroscopic data and its application to studying turbulence and magnetic fields
- Polarimetric studies of magnetic turbulence with interferometer
- On the Existence of Fast Modes in Compressible Magnetohydrodynamic Turbulence
- Nature and Scalings of Density Fluctuations of Compressible MHD Turbulence with Applications to the Solar Wind
- Obtaining magnetic field strength using differential measure approach and velocity channel maps
- Turbulent universal galactic Kolmogorov velocity cascade over 6 decades