Simulation study of energetic electron bursts from reforming shocks

Details Simulation study of energetic electron bursts from reforming shocks Simulation study of energetic electron bursts from reforming shocks

May 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agusmsh23a..04y&link_type=abstract

American Geophysical Union, Spring Meeting 2009, abstract #SH23A-04

Physics

7851 Shock Waves (4455)

Scientific paper

Collisonless shocks redistribute energy, heating and accelerating electrons responsible for various plasma waves and emissions in the upstream and downstream shock region. In this paper we study numerically the electron dynamics in time-dependent shock fields generated by an one-dimensional multiscale hybrid code, and steady state model shocks by tracing the exact test particle electron trajectories. It is shown that the upstream energetic electron bursts are produced cyclically at the shock reformation period in the time- dependent reforming shocks providing the upstream shock Mach number and plasma beta is high and low enough, respectively. Observation of the upstream electron distribution functions shows time-varying loss cone structures and beam features. In contrast to the reforming shocks, a continous electron beam is formed by the reflected electrons in upstream of steady state model shocks. Parameter study shows that the upstream incoming electrons can be reflected non-uniformly or continuously depending on the shock parameters. Bursty energetic electron events take place when the plasma beta is low (β ≤ 0.4) and the shock Mach number is high (MA≥ 6). In contrast, continuously reflected electrons are observed for low beta (β ≤ 0.4), low Mach number (MA ≤ 4) shocks, even when the shock is reforming, because the changes in shock fields are relative small. The electron burst events disappear and the observed upstream electron distribution function contours are steady-state. A continuous electron beam is formed which is qualitative the same as the beam from steady-state shocks. Increasing the plasma beta (providing the shock is still reforming) has minor effects on the upstream electron beam features. This calculation demonstrates that shock nonstationarity may lead to major changes in electron distributions and associated plasma waves upstream and downstream depending on the upstream shock parameters, probably requiring modification to the steady state shock model used for predicting foreshock radio emission.

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