A complete model of the propagation of solar-flare cosmic rays |
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| Authors: | C K Ng L J Gleeson |
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| Institution: | (1) University of Malaya, Kuala Lumpur, Malaysia;(2) Monash University, 3168 Clayton, Australia |
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| Abstract: | A two-stage model of the propagation of 1–50 MeV solar-flare cosmic rays is presented. The first stage consists of a thin spherical shell of radius r
a near the Sun which feeds particles into interplanetary space (the second stage) where they propagate along the Archimedean mean interplanetary magnetic field under the influences of anisotropic diffusion, convection, and energy changes. To calculate the time dependence at a fixed point in space, account is taken of the corotation of flux tubes past the observer.It is shown that the well-known east-west effect of the time-to-maximum cannot be obtained if the injection from the first stage is impulsive and thus a time and longitude dependent release for the second stage is essential. This is achieved by treating the first stage as a thin, spherical, diffusing shell of radius r
a with diffusion coefficient 
s, from which particles leak into interplanetary space at a rate determined by the leakage coefficient  .With this model we are able to reproduce simultaneously four principal features of solar events observed at r = 1 AU: (i) the east-west effect, i.e. the time-to-maximum as a function of flare longitude; (ii) the three phases of the anisotropy vector variation; (iii) the time-to-convective-phase as a function of flare longitude; and (iv) the longitudinal distribution of the differential intensity. Our best estimates of the parameters of the near-Sun propagation are that 0.01 hr–1 
s/r
a
2
0.02 hr–1 and 1/15 hr–1  1/10 hr–1. For the interplanetary propagation we estimate /V  - 1.2AU with , the effective cosmic-ray diffusion coefficient and V, the solar-wind speed. |
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