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DY: Fachverband Dynamik und Statistische Physik
DY 32: Focus Session: Statistics of fully developed turbulence
DY 32.2: Vortrag
Mittwoch, 18. März 2015, 15:30–15:45, BH-N 243
The non-universality of magnetohydrodynamic turbulence — •Wolf-Christian Müller1, Roland Grappin2, Andrea Verdini3, and Özgur Gürcan4 — 1Technische Hochschule Berlin, Plasma-Astrophysik — 2LUTH, Observatoire de Paris and LPP, Ecole Polytechnique, France — 3Università di Firenze, Dipartimento di Fisica e Astronomia, Firenze, Italy and Royal Observatory of Belgium, SIDC/STCE, Brussels — 4LPP, Ecole Polytechnique, Paris, France
We present a new cascade scenario motivated by the three-dimensional energy spectrum observed in numerical simulations of incompressible MHD turbulence in a strong mean field. It is shown that the energy distribution is not in accord with standard critical balance and the associated scale anisotropy. In spite of this, a measurable anisotropy of structure-function scaling exists independent of taking spatial increments with respect to the mean or local direction of the magnetic field.
We, thus, propose a combination of weak Iroshnikov-Kraichnan dynamics governing energy transfer in the field-perpendicular plane and the ricochet process distributing energy quasi-resonantly along all other directions. This spectral transfer process asymptotically approaches the 2D IK-cascade as B0 increases. The new transfer mechanism is at variance with the commonly accepted resonant weak-turbulence cascade as well as with the critically balanced strong turbulence cascade. It is shown that the non-universal spectral dynamics are determined by the large-scale ratio of kinetic and magnetic energy.