Jets downstream of the Earth’s bow shock

The downstream region of a collisionless quasi-parallel shock is structured containing localized bulk flows with high kinetic energy density and dynamic pressure. In 2009, we presented Cluster multi-spacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock within the sheath. These observations allowed us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasi-parallel shocks can create fast, slightly 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 surrounding flow and/or the magnetopause, a second shock front forms in the sheath.

During the following years, magnetosheath jets have been a continually active research topic. Studies using increasingly large databases of spacecraft observations have gathered the statistics of jet formation conditions and properties. Simulations and case studies have shed light on jet formation mechanisms. Within the magnetosheath, the jet-driven secondary bow waves/shocks have been shown to contribute to particle energization. Investigations of jet impacts on the magnetosphere have revealed a plethora of effects, ranging from surface waves and magnetopause reconnection to diffuse auroral brightenings.

In this talk, we will summarize the progress to date and highlight some still open questions.