Particle Acceleration by Magnetosheath Jet-driven Bow Waves

Localized magnetosheath jets with high dynamic pressure are frequently observed downstream of Earth's bow shock. When such a fast magnetosheath jet compresses the ambient magnetosheath plasma, an earthward compressional bow wave could form. Such bow waves have been predicted by simulations but have never been observed. Using multipoint THEMIS observations, we report the first observation of such a bow wave which can accelerate particles. Using case studies, we demonstrate how jet-driven bow waves accelerate ions and electrons. Using statistical studies, we reveal the favorable formation condition of such bow waves and show that their particle acceleration is common. Our study implies that particle acceleration at jet-driven bow waves could contribute significantly to particle acceleration at shocks in general. As high Alfven Mach number of the parent shock favors the formation of jet-driven bow waves, their contribution may be even more important at high Mach number astrophysical shocks.