SSP seminar

Balanced and Imbalanced MHD Turbulence

Andrey Beresnyak (Los Alamos National Laboratory)

Monday 14th February 2011, 12:00 noon
Pratt conference room, 60 Garden Street

Magnetohydrodynamic turbulence is present in almost all astrophysical environments. Its properties are important for the dynamics of the intracluster medium, interstellar medium, it affects star formation rate in molecular clouds, transport properties of astrophysical fluids, etc. The spectral slope of strong MHD turbulence has been a matter of controversy. While Goldreich-Sridhar model (1995) predicts Kolmogorov's -5/3 slope, shallower slopes were reported by numerics. I will present recent high-resolution simulations of MHD turbulence that support Kolmogorov's -5/3 spectral slope of MHD turbulence. For the first time we were able to measure the Kolmogorov constant of MHD turbulence, which quantifies the efficiency of energy cascade, C_K=4.1+-0.3. It is much higher than hydrodynamic C_K=1.64, that is MHD turbulence with the same energy will produce about four times less dissipation than hydro turbulence. This has immediate consequences for the turbulent heating in the ISM. The general case of MHD turbulence, so-called imbalanced turbulence is most common in nature, as strong turbulence is often observed near the energetic source of perturbations. I will explain the challenge in making a consistent model of imbalanced turbulence and review currently existing theories and numerics.


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