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The correlation between magnetic pressure and density in compressible MHD turbulence. (English) Zbl 1027.76066
The authors perform analytical and numerical study of magnetic pressure and density fluctuations in isothermal MHD flows in a slab geometry. Simple MHD waves are considered, which are nonlinear analogue of slow, fast and Alfvén linear waves. The authors examine the dependence of magnetic field on density in simple waves, and it is shown that a wide variety of examples indicates that a single polytropic description of magnetic pressure is not possible in general, but depends on which mode dominates the density fluctuation. This depends on the angle between magnetic field and the direction of wave propagation, and on Alfven number. These results have implications for probability density function of mass density. The results are consistent with apparent lack of correlaton between magnetic field and density in lower-density molecular gases. Numerical simulations are carried out to test the range of validity of the model calculations. Finally, possible implications on molecular clouds are formulated.

76W05 Magnetohydrodynamics and electrohydrodynamics
76F50 Compressibility effects in turbulence
85A30 Hydrodynamic and hydromagnetic problems in astronomy and astrophysics
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