Energy Partition at a Collisionless Supercritical Quasi‐Parallel Shock

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Abstract
Shocks in collisionless astrophysical plasmas redistribute some of the incident flow energy into both thermal and non‐thermal energy. Quantifying the partition of that energy amongst various particle species or their sub‐populations, and electromagnetic energy, represents a fundamental goal of shock physics. It embodies the role of the equation of state for the system. Here we apply a framework to assess all the incident and downstream energy fluxes at a crossing of Earth's bow shock for which the upstream magnetic field was roughly aligned with the shock normal direction. Such quasi‐parallel shocks are known to be non‐steady and to produce significant populations of suprathermal particles. We quantify the evolution of all the important carriers of energy flux through the shock region. We sub‐divide the proton population into thermal, suprathermal, and energetic components in order to investigate the shock's efficiency in energizing the nonthermal particles. While the largest energy fluxes are found in the incident proton ram energy and downstream proton thermal enthalpy fluxes, a significant suprathermal population pervades the regions both up‐ and downstream. We also evaluate the energy fluxes attributable to fluctuations in the fluid and field parameters.

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