Mathematics – Probability
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...209.8424h&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #84.24; Bulletin of the American Astronomical Society, V
Mathematics
Probability
Scientific paper
Turbulence is extremely important for many astrophysical processes including star formation, transport of heat, and cosmic ray propagation. For astrophysical media that are both magnetized and compressible, it is important to address the differences that magnetic fields and compressibility make in turbulence. A comparative study is performed of changes that arise in the velocity statistics, or turbulent motions, as a result of individually including an external magnetic field and compressibility. The following three models of turbulence are used: incompressible hydrodynamic, incompressible magnetohydrodynamic (MHD), and compressible MHD. The compatibility of the spectra of all three models with the Kolmogorov spectrum is confirmed, suggesting that the energy transfer process is consistent for all three models. For the MHD models the probability distribution functions of the velocity components in the plane perpendicular to the external magnetic field are like the incompressible hydrodynamic model while those parallel are not. It is found that high order longitudinal statistics in both the global reference frame and in the frame perpendicular to the local mean magnetic field are extremely similar for all three models, while those in the frame parallel to the local mean field are not. We therefore conclude that turbulent motions in the plane perpendicular to the local mean field are affected very little by the inclusion of an external magnetic field and compressibility, while those parallel are affected significantly. The statistics are then decomposed into Alfvenic, fast, and slow modes. It is found that the Alfven mode is mostly responsible for the above-mentioned results in both frames. It is also shown that high order longitudinal statistics in the plane perpendicular to the local mean field for the Alfvenic mode are similar for both MHD models. Our study clarifies the extent to which magnetic fields are important for different astrophysical processes.
Cho Jungyeon
Hall Nicholas
Kowal Grzegorz
Lazarian Alex
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