Modeling the effects of the pitch-angle scattering processes on the transport of energetic particles along the interplanetary magnetic field
Abstract
We have studied the time-dependent transport of energetic particles in the interplanetary medium using a Monte Carlo approach. We use the guiding center approximation between discrete finite pitch-angle scatterings to quantify the effects of focusing on energetic particles propagating along a Parker spiral magnetic field in the fixed (corotating) frame. Because the small-scale irregularities in the field can be considered to be frozen in the solar wind, we simulate elastic scatterings in the local solar wind frame in order to study the impact on the adiabatic energy losses of solar energetic particles on the near-Earth intensity profiles. Unlike most previous formulations of this problem, we use a joint probability distribution P(Δ s,μ')=p(Δ s;μ')q(μ';μ). Here p(Δ s;μ') is the conditional probability that the particle travels a distance (Δ s) along the field line before the next scattering if it had a pitch cosine (μ') after the previous scattering, and q(μ';μ) is the conditional probability for the pitch cosine μ' given that the pitch angle was μ before the previous scattering. Both conditional probabilities may be functions of the position along the field line of the scattering. We find that both the pitch-angle distributions and the time-intensity profiles observed at 1 AU strongly depend on the forms assumed for the conditional probabilities. For example, if the conditional dependence on the prior pitch-cosine (μ') in p(Δ s;μ') is ignored (as has often been done in previous analyses), it produces an unphysical "bite-out" around pitch angles of 90^o (μ=0) in the angular distributions that is never seen in particle observations at 1 AU.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.2918A