Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh41c..03o&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH41C-03
Physics
Plasma Physics
[7827] Space Plasma Physics / Kinetic And Mhd Theory, [7863] Space Plasma Physics / Turbulence
Scientific paper
Magnetohydrodynamic (MHD) turbulence provides a useful framework for understanding the nature and behavior of solar wind fluctuations1. We present a review of MHD turbulence in the solar wind context, where typically δ B / B0 ˜ 1, rather than ≤ 1. Here B0 denotes the mean or large-scale magnetic field and δ B the rms fluctuation amplitude. We will discuss various consequences of the the well-known anisotropy induced by B0 . For example, the energy transfer is no longer isotropic, with transfer in directions approximately perpendicular to B0 remaining strong whereas parallel transfer is suppressed. Thus, differences in the slope of the energy spectrum in the perpendicular and parallel directions are to be expected. This in turn has implications for scattering of energetic particles. Another consequence of the suppression of parallel transfer is that it restricts the energy available to any kinetic processes which act at large parallel wavenumbers, e.g., ion-cyclotron damping. Since such kinetic processes are likely to be involved in the heating of solar wind fluctuations, the anisotropy of spectral transfer influences heating processes. On the modeling front, anisotropy of spectral transfer helps motivate treating the fluctuations as belonging to two distinct groups, conveniently referred to as the quasi-two-dimensional and the wave-like components. The partitioning is based on the ratio of the nonlinear timescale τ NL(k) to the Alfvén timescale τ A( k) at each wavevector k (see figure). The self interaction of the quasi-2D component is predominantly nonlinear with wave effects being relatively weak. For the wave-like component, the situation is, roughly speaking, reversed. Our presentation will review these concepts and the associated physics. The relevance of the equations of Reduced MHD---originally developed for δ B / B0 ≤ 1---to solar wind plasma is also discussed. 1 Bruno, R. and Carbone, V., The Solar Wind as a Turbulence Laboratory, Liv. Rev. Sol. Phys., 2 (2005)
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