Superdiffusive transport of electrons accelerated at corotating interaction regions
Abstract
Energetic particles in the solar wind are accelerated at interplanetary shock waves associated with corotating interaction regions (CIRs) and propagate in the presence of a spectrum of magnetic turbulence, which causes pitch angle scattering upstream of the shock. Besides normal diffusive transport, we study the possibility of superdiffusive transport characterized by Levy random walks. We consider the relevant propagator, which is a power law with slope 2 < μ < 3, instead of being a Gaussian, as for standard diffusion. We show that in the case of superdiffusive transport, the time profile of particles accelerated at a travelling planar shock is a power law with slope γ = μ-2, rather than an exponential decay as expected in the case of normal diffusion. We consider a data set of interplanetary shocks in the solar wind, the CIR-associated forward and reverse shocks detected by Ulysses between January 1992 and May 1993. We find that the time profiles of energetic electrons, with energies between 42 and 290 keV, correspond to power laws, with slopes γ≃ 0.60-0.98, implying superdiffusive transport. These results show that the propagation of energetic electrons in the turbulent environment of the solar wind is intermediate between ballistic (or scatter-free) and diffusive, in agreement with the results of recent numerical simulations. Our results promise to have application in models of shock particle acceleration and represent a new tool for the interpretation of the observed particle profiles throughout the heliosphere.
- Publication:
-
Journal of Geophysical Research (Space Physics)
- Pub Date:
- March 2008
- DOI:
- 10.1029/2007JA012695
- Bibcode:
- 2008JGRA..113.3107P
- Keywords:
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- Solar Physics;
- Astrophysics;
- and Astronomy: Energetic particles (2114);
- Space Plasma Physics: Transport processes;
- Space Plasma Physics: Turbulence (4490);
- Space Plasma Physics: Shock waves (4455);
- Space Plasma Physics: Particle acceleration;
- energetic particles;
- transport processes;
- Levy walks