Numerical studies of the transport of solar protons in interplanetary space |
| |
Authors: | S Webb JJ Quenby |
| |
Institution: | Physics Department, Imperial College, London, S.W.7, England |
| |
Abstract: | Numerical solutions of the Fokker-Planck equation governing the transport of solar protons are obtained using the Crank-Nicholson technique with the diffusion coefficient represented by Kr=K0rb where r is radial distance from the Sun and b can take on positive or negative values. As b ranges from +1 to ?3, the time to the observation of peak flux decreases by a factor of 5 for 1 MeV protons when where V is the solar wind speed. The time to peak flux is found to be very insensitive to assumptions concerning the solar and outer scattering boundary conditions and the presence of exponential time decay in the flux does not depend on the existence of an outer boundary. At , 1 MeV particles come from the Sun by an almost entirely convective process and suffer large adiabatic deceleration at b?0 but for b=+1, large Fermi acceleration is possible at all reasonable values. Implications of this result for the calculation and measurement of particle diffusion coefficients is discussed. At , the pure diffusion approximation to transport overestimates by a factor 2 or more the time to peak flux but as b becomes more negative, the additional effects of convection and energy loss become less important. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|