Cranmer, S. R. 2000, ``Kinetic Coronal Heating,'' in Physics of Space: Growth Points and Problems, Meudon, France, 10-14 January 2000 (Invited Talk).


This talk will review the kinetic origins of several physical processes that are thought to heat the solar corona and accelerate solar wind particles. Classical dissipative phenomena (viscosity, heat conductivity, electrical resistivity) depend mainly on the strength of Coulomb collisions in the corona, but many collisionless channels for, e.g., wave or current dissipation have been proposed. Specifically, the damping of high frequency (10 to 10,000 Hz) ion cyclotron resonant Alfven waves has been proposed as a leading candidate for ion energization in the high-speed solar wind. The spectroscopic and in situ observations that have led to this conclusion will be reviewed. The ion cyclotron resonance produces a non-standard type of pitch-angle scattering in velocity space which can be expressed as a nonlinear diffusion equation. Test solutions of this equation showing the natural development of large perpendicular kinetic temperatures will be presented. Because ions with very low abundances can damp the waves, it is necessary to take a large number of ion species into account, and the summed effect of more than 2000 minor ions will be discussed. The surprisingly effective damping ability of minor ions can be understood in simple terms by applying the Sobolev approximation from the theory of hot-star winds. The mean state of the coronal and heliospheric plasma is intimately coupled with kinetic fluctuations about that mean, and theories of turbulence, wave dissipation, and instabilities must continue to be developed along with steady state solar wind models.

This work is supported by the National Aeronautics and Space Administration under grant NAG5-7822 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the ESA PRODEX program (Swiss contribution).

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