Fokker-Planck theory for cosmic ray diffusion in the presence of Alfven waves. II - Model stream calculation

Details Fokker-Planck theory for cosmic ray diffusion in the presence of Alfven waves. II - Model stream calculation Fokker-Planck theory for cosmic ray diffusion in the presence of Alfven waves. II - Model stream calculation

Dec 1976

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976jgr....81.5887s&link_type=abstract

Journal of Geophysical Research, vol. 81, Dec. 1, 1976, p. 5887-5899.

Physics

2

Cosmic Rays, Diffusion Coefficient, Fokker-Planck Equation, Magnetohydrodynamic Waves, Particle Diffusion, Solar Wind, Diffusion Theory, Galactic Radiation, Plasma-Particle Interactions, Protons, Radial Distribution, Solar Cosmic Rays, Solar Wind Velocity

Scientific paper

The paper investigates the cosmic-ray radial diffusion coefficient resulting from linearly polarized Alfven waves propagating outward through an azimuthally structured solar wind. The analysis utilizes a diffusion coefficient derived from quasi-linear Fokker-Planck theory and a model solar-wind stream in which the solar-wind velocity varies linearly with azimuth. It is found that beyond 1 AU, the stream significantly reduces the diffusion coefficient below that for a spherically symmetric solar wind. The diffusion coefficient is also found to reach a minimum value at a heliocentric distance of approximately 75 solar radii, and this minimum moves outward with increasing steepness of the wave spectrum. The diffusion coefficient is a separable function of radius and rigidity below approximately 0.5 GV, but at higher rigidities it is found that the separability fails. It is concluded that the present diffusion theory is consistent with a cosmic-ray gradient which decreases slowly with heliocentric distance and has a mean value, between 1 and 5 AU, of about 3%/AU for 1-GeV galactic protons.

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