Supermagnetosonic jets behind a collisionless quasi-parallel shock

TL;DR

This paper reports on the discovery and analysis of supermagnetosonic jets behind collisionless quasi-parallel shocks, revealing a new generation mechanism involving shock curvature and secondary shock formation, with implications for plasma environments.

Contribution

It introduces a novel generation mechanism for supermagnetosonic jets in collisionless shocks based on spacecraft observations and shock curvature effects.

Findings

Identification of supermagnetosonic jets in the downstream region.

Detection of a secondary shock front within the sheath.

Proposed mechanism linking shock curvature to jet formation.

Abstract

The downstream region of a collisionless quasi-parallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multi-spacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasi-parallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasi-parallel shocks in many plasma environments.