Hybrid Simulations of ion Acceleration at Interplanetary Shocks: Decoupling From the Wave Turbulence on Large Scales and Resulting Flux Profiles

Details Hybrid Simulations of ion Acceleration at Interplanetary Shocks: Decoupling From the Wave Turbulence on Large Scales and Resulting Flux Profiles Hybrid Simulations of ion Acceleration at Interplanetary Shocks: Decoupling From the Wave Turbulence on Large Scales and Resulting Flux Profiles

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh23c..08k&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH23C-08

Other

2139 Interplanetary Shocks, 7845 Particle Acceleration, 7851 Shock Waves (4455), 7867 Wave/Particle Interactions (2483, 6984), 7959 Models

Scientific paper

Several different methods have been developed over the past years to make progress in calculating and predicting solar energetic particles (SEPs) that result from CME-driven shocks - also to forecast their associated hazards. Ion acceleration at interplanetary (IP) shocks involves complex processes that happen on vastly different scales, from the thermal ion scales of the kinetic shock transition to those of the transport and radial plasma changes in the solar wind environment. We have adopted an approach that separates these scales by assuming energization takes place in a limited region, outside of which the particles are assumed to more or less freely stream along the interplanetary magnetic field (IMF). In this approach, both the shock strength and IMF can be obtained from MHD simulations, while the energetic ion fluxes may be derived form the known shock parameters via heuristic methods, from shock acceleration theory, or from particle simulations. In the past, however, such particle simulations were very local. That is, they only described the local enhancement of energetic ions at the shock, what corresponds to observed ESP events, when the CME-driven IP shock passes the spacecraft. We have previously shown that for parallel and slightly oblique shocks, the resulting peak fluxes at moderate energies agree well with observations at undisturbed, isolated events. However, modeling of the arriving SEPs at Earth (or other locations of interest) from remote shocks also requires knowledge of the freely streaming fluxes and their pitch angle distributions, once the energetic ions are decoupled from the wave turbulence surrounding the shock. Here we present results of sufficiently large hybrid simulations (kinetic ions, electron fluid) that allow us to study the decoupling of the energetic ions with distance from the shock, and its dependence on energy. We compare the calculated flux profiles with those derived from ACE observations, and illustrate how our results can be used in global SEP model calculations.

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