Energy Balance at Interplanetary Shocks: In-situ Measurement of the Fraction in Supra-thermal and Energetic Particles with ACE and Wind

TL;DR

This study measures the energy transfer to supra-thermal and energetic particles at interplanetary shocks using ACE and Wind data, revealing that 2-16% of upstream energy flux is transferred, independent of shock speed or magnetic orientation.

Contribution

It provides the first in-situ measurements of the fraction of energy transferred to non-Maxwellian particles at interplanetary shocks, using a comprehensive dataset from ACE and Wind.

Findings

2-16% of upstream energy flux is transferred to non-Maxwellian particles.

No correlation between shock Mach number or magnetic field angle and particle pressure.

In-situ measurements quantify energy balance at interplanetary shocks.

Abstract

The acceleration of charged particles by interplanetary shocks can drain a non-negligible fraction of the upstream ram pressure. For a sample of shocks observed in-situ at 1 AU by the ACE and Wind spacecraft, time-series of the non-Maxwellian components (supra-thermal and higher-energy) of the ion and electron energy spectra were acquired for each event. These were averaged for one hour before and after the time of the shock passage to determine their partial pressure. Using the MHD Rankine-Hugoniot jump conditions, we find that the fraction of the total upstream energy flux transferred to non-Maxwellian downstream particles is typically about 2-16%. Notably, our sample shows that neither the fast magnetosonic Mach number nor the angle between the shock normal and average upstream magnetic field are correlated with non-Maxwellian particle pressure.