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Titel |
Three-dimensional Iroshnikov-Kraichnan Turbulence in a Mean Magnetic Field |
VerfasserIn |
Wolf-Christian Müller, Roland Grappin, Andrea Verdini, Özgür Gürcan |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250104037
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Publikation (Nr.) |
EGU/EGU2015-3457.pdf |
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Zusammenfassung |
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. This is not surprising as the present setup with isotropic
large-scale forcing predominantly yields fluctuations in the weak-turbulence regime.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 turbulence properties are consistent with the
main numerical findings, in particular, regarding the energy spectrum: (i) an inertial-range
power law exponent independent of direction, (ii) a direction-dependent power-law
spectral-range extent ~ brms/B0. 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,
both resulting in strictly perpendicular energy transfer. This is necessary to explain the
significant field-parallel extent of the observed energy distribution, The findings also disagree
with the small-scale dynamic-alignment phenomenology.
It is shown that the non-universal spectral dynamics are determined by the large-scale
ratio of kinetic and magnetic energy. |
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