Physics – Plasma Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh42a..01m&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH42A-01
Physics
Plasma Physics
[7524] Solar Physics, Astrophysics, And Astronomy / Magnetic Fields, [7811] Space Plasma Physics / Discontinuities, [7827] Space Plasma Physics / Kinetic And Mhd Theory, [7835] Space Plasma Physics / Magnetic Reconnection
Scientific paper
Descriptions of magnetic field and plasma structures in terms of flux tubes, plasmoids and other bundles of magnetic field lines are familiar in the vocabulary of observational and theoretical space physics. "Spaghetti models" and flux ropes are well known examples. Flux tubes and families of field lines can also be defined in a medium that admits magnetic fluctuations, including strong MHD turbulence, but their behavior can become complicated. In 3D fluctuations the smooth flux tube description itself becomes in some sense unstable, as nearby field lines diverge and flux surfaces shred. This lends complexity to the structure of flux tubes, and can give rise to temporarily trapped field lines and charged test particle trajectories, with immediate implications for transport, e.g., of solar energetic particles. The properties of the turbulent magnetic field can also be strongly influenced by the dynamics of turbulence. Large scale self organizing behavior, or inverse cascade, can enhance very long wavelength structure, favoring Bohm scaling of diffusion coefficients. Meanwhile smaller scale flux tube structures are integral features of the inertial range of turbulence, giving rise to a cellularization of the plasma due to rapid dynamical relaxation processes. These drive the turbulent system locally towards low-acceleration states, including Alfvenic, Beltrami and force-free states. Cell boundaries are natural positions for formation of near discontinuous boundaries, where dynamical activity can be enhanced. A primary example is appearance of numerous discontinuities and active reconnection sites in turbulence, which appear to support a wide distribution of reconnection rates associated with coherent current structures. These discontinuities are also potential sites of enhanced heating, as expected in Kolmogorov's Refined Similarity Hypothesis. All of these features are related to self organization, cascade and intermittency of the turbulence. Examples of these features in simulation data and in solar wind observations will be presented and discussed.
Greco Andrés
Matthaeus William H.
Osman K.
Ruffolo David J.
Servidio Sergio
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