Radial dependence of proton peak intensities and fluences in SEP events: Influence of the energetic particle transport parameters

We study the radial dependence of peak intensities and fluences of solar energetic particle (SEP) events in the framework of the focused transport theory. We solve the focused-diffusion transport equation that includes the effects of solar wind convection, adiabatic deceleration and pitch-angle scattering. We assume a Reid–Axford time profile for the particle injection at the base of a flux tube described by an Archimedean spiral magnetic field whose cross section A(r) expands as r 2 cos(w), where r is the radial distance and w(r) is the angle between the magnetic field line and the radial direction. We assume that energetic particles propagate along the field line. We locate several observers along the flux tube at radial distances ranging from 0.3 to 1.6 AU. Both peak intensities and event fluences decrease with increasing radial distance. We deduce functional forms to extrapolate peak fluxes and fluences with radial distance that depend on the energy of the particles, the pitch-angle scattering conditions, and the duration of the particle injection. The smaller the mean free path of the particles, the larger the decrease of both peak intensities and fluences with radial distance. The smaller the energy of the particles, the larger the decrease of both peak intensities and fluences with radial distance. Extended particle injections contribute to soften the decrease of the peak intensities with the radial distance but have no influence on the event fluence. We note that mobile particle sources (i.e. traveling interplanetary shocks) may vary the radial dependences deduced in this work. 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

[1]  Energetic Particle Events: Efficiency of Interplanetary Shocks as 50 keV < E < 100 MeV Proton Accelerators , 1998 .

[2]  D. Lario,et al.  Fluxes and fluences of SEP events derived from SOLPENCO , 2005 .

[3]  G. Reid.  A diffusive model for the initial phase of a solar proton event , 1964 .

[4]  A. Ruzmaikin,et al.  The Radial Dependence of Solar Energetic Particle Fluxes , 2005 .

[5]  M. Shea,et al.  Toward a descriptive model of solar particles in the heliosphere , 1988 .

[6]  S. Krimigis,et al.  Radial and Longitudinal Dependence of Solar 4-13 MeV and 27-37 MeV Proton Peak Intensities and Fluences: Helios and IMP 8 Observations , 2006 .

[7]  T. Sanderson,et al.  Observational signatures of the influence of the interplanetary shocks on the associated low‐energy particle events , 1994 .

[8]  Rami Vainio,et al.  Modeling of Solar Energetic Particles in Interplanetary Space , 2007 .

[9]  M. Mason,et al.  The Radial Dependence of the Peak Flux and Fluence in Solar Energetic Particle Events , 1990 .

[10]  Eugene N. Parker,et al.  THE PASSAGE OF ENERGETIC CHARGED PARTICLES THROUGH INTERPLANETARY SPACE , 1965 .

[11]  D. Hamilton.  The radial dependence of the solar energetic particle flux , 1988 .

[12]  Bernhard Fleck,et al.  The solar orbiter mission , 2003 .

[13]  M. Shea,et al.  Comment on estimating the solar proton environment that may affect Mars missions. , 2003, Advances in space research : the official journal of the Committee on Space Research.

[14]  David Lario i Loyo.  Propagation of low-energy particles through the interplanetary medium: modeling their injection from interplanetary shocks , 1997 .