Kinetic Properties of an Interplanetary Shock Propagating inside a Coronal Mass Ejection

TL;DR

This study analyzes the kinetic behavior of an interplanetary shock within a coronal mass ejection using in situ Wind measurements, revealing ion gyration, electron scattering, and wave interactions that influence shock dynamics.

Contribution

It provides detailed observations of particle distributions and wave phenomena at kinetic scales inside an ICME shock, highlighting new insights into shock-ICME interactions.

Findings

Gyrating ions observed around the shock ramp suggest energy dissipation mechanisms.

Enhanced proton temperature anisotropy constrained by low plasma beta prevents certain instabilities.

Whistler waves and heat flux instabilities influence electron dynamics and shock decay.

Abstract

We investigate the kinetic properties of a typical fast-mode shock inside an interplanetary coronal mass ejection (ICME) observed on 1998 August 6 at 1 AU, including particle distributions and wave analysis with the in situ measurements from Wind. Key results are obtained concerning the shock and the shock-ICME interaction at kinetic scales: (1) gyrating ions, which may provide energy dissipation at the shock in addition to wave-particle interactions, are observed around the shock ramp; (2) despite the enhanced proton temperature anisotropy of the shocked plasma, the low plasma beta inside the ICME constrains the shocked plasma under the thresholds of the ion cyclotron and mirror-mode instabilities; (3) whistler heat flux instabilities, which can pitch--angle scatter halo electrons through a cyclotron resonance, are observed around the shock, and can explain the disappearance of bidirectional electrons inside the ICME together with normal betatron acceleration; (4) whistler waves near the shock are likely associated with the whistler heat flux instabilities excited at the shock ramp, which is consistent with the result that the waves may originate from the shock ramp; (5) the whistlers share a similar characteristic with the shocklet whistlers observed by Wilson et al, providing possible evidence that the shock is decaying because of the strong magnetic field inside the ICME.