Springer Online Journal Archives 1860-2000
Abstract A statistical analysis of solar particle events, observed by the GSFC-UNH charged particle detector on board Pioneer 10 and Pioneer 11 from March 1972 to December 1974 (from 1 to 5 AU for each spacecraft), is carried out with the goal of experimentally determining the statistical average interplanetary propagation conditions from 3 to 30 MeV. A numerical propagation model is developed that includes diffusion with a diffusion coefficient of the form k r =k o r β , convection, adiabatic deceleration, and a variable coronal injection profile. The statistical analysis is carried out by individually analyzing each of five parameters (t max, ξ(tmax), Δt 5, τ) that are uniquely defined in a solar particle event. Each of the five parameter data sets were analyzed in terms of both a spacecraft-solar flare connection longitude ≤50°, and a numerical model that employed a variable exponential decaying coronal injection profile. The five individual parameter analyses are combined with the results that the statistical average radial interplanetary diffusion coefficient from 1 to 5 AU is given by 〈k r〉 = (1.2 ± 0.4) × 1021 cm2 s-1 with 〈β〉 = 0.0± 0.3 for 3.4 to 5.2 MeV protons and 〈k r〉 = (2.6 ± 0.6) × 1021 cm2 s-1 with (β) = 0.0± 0.3 for 24 to 30 MeV protons. Using the classical relationship for the radial scattering mean free path λr, i.e. k r = υλr/3, we obtain 〈λr〉 = 0.09 ± 0.03 AU and 0.075 ± 0.020 AU for the low and high energy data, respectively. These results show, from 1 to 5 AU and from 3 to 30 MeV, that 〈λr〉 is both independent of radial distance and approximately independent of rigidity (for 〈λr〉~P α, where P = rigidity, α = -0.15 ± 0.20). The above diffusion coefficients are inconsistent With both the predictions of the diffusion coefficient from present theoretical transport models and with the diffusion coefficient used in modulation studies at low energies.
Type of Medium: