Spectral Maps of Collisionless-MHD Turbulence in k{∥ }-k⊥ Space

Details Spectral Maps of Collisionless-MHD Turbulence in k{∥ }-k⊥ Space Spectral Maps of Collisionless-MHD Turbulence in k{∥ }-k⊥ Space

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsh51c0283b&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SH51C-0283

Physics

7863 Turbulence, 7867 Wave/Particle Interactions, 2149 Mhd Waves And Turbulence, 2159 Plasma Waves And Turbulence, 2164 Solar Wind Plasma

Scientific paper

For turbulence in fluids, the energy cascade is famously depicted by a one-dimensional (omnidirectional) wavenumber spectrum that is divided into three regions: an energy subrange at small k, an inertial subrange at intermediate k, and a dissipation subrange at large k. Eddy-eddy interactions produce a net flow of energy from small-k to large-k. For turbulence in collisionless plasmas, the magnetic field {ěc B} of the plasma defines a coordiante system with behavior parallel to{ěc B} differing from behavior perpendicular to {ěc B}. A map of MHD turbulence in k∥ -k⊥ space is considered. Owing to the magnetic field, every turbulent fluctuation in a plasma has an eddy nature and an Alfven-wave nature. The wave nature of the fluctuations has two major effects. First, the wave nature splits the inertial subrange into two regions in k∥ -k⊥ space: a region where eddy-eddy interactions happen more quickly than Alfven-wave effects (the Kolmogorov-turbulence region at k⊥ ≫ k∥ ) and a region where eddy-eddy interactions happen more slowly than Alfven-wave effects (the Kraichnan-turbulence region at k⊥ ≤ k∥ ). Second, the wave nature of the fluctuations allows wave-particle interactions to dissipate the turbulence. The boundary ("inner scale") between the inertial subrange and the dissipation subrange is a curve in k∥ -k⊥ space that depends on where electron Landau damping, ion Landau damping, or ion cyclotron damping dominates over eddy-eddy energy transfer, which differs for left-hand-polarized (Alfven-cyclotron branch) and right-hand-polarized (magnetosonic-whister branch) turbulent fluctuations. For solar-wind turbulence, the two k∥ -k⊥ maps are drawn: one for the left-hand fluctuations in the turbulence and one for the right-hand fluctuations in the turbulence.

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