Fokker-Planck theory for cosmic ray diffusion in the presence of Alfvén waves 2. Model stream calculation
Abstract
We investigate the cosmic ray radial diffusion coefficient resulting from linearly polarized Alfvén 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 minumum value at a heliucentric distance of approximately 75 Rs, 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. Finally, it is concluded that the present diffusion theory is consistent with a cosmic ray gradient which decreases slowly with r and has a mean value, between 1 and 5 AU , of about 3%/AU for 1-GeV galactic protons.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- December 1976
- DOI:
- 10.1029/JA081i034p05887
- Bibcode:
- 1976JGR....81.5887S
- Keywords:
-
- 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