High-Speed Jets and Magnetic Reconnection in Earth’s magnetosheath: MMS observations

High-speed jets are transient structures in the magnetosheath characterized by high dynamic pressure. Their compressed magnetic field lines at the leading edge can generate bow waves, which are believed to accelerate particles and enhance energy dissipation in the magnetosheath. In this study, we analyzed a typical event within the magnetosheath, using observations from the Magnetospheric Multiscale (MMS) mission. Results reveal that during the MMS traversal of the magnetosheath, it captured for the first time a complete spatiotemporal co-occurrence of three structures: the high-speed jet, bow wave, and magnetic reconnection. Notably, the reconnection took place at the leading edge of the high-speed jet and bow wave, suggesting a potential mechanism for magnetosheath reconnection: high-speed jets propel bow waves, which then compress the pre-existing, curved magnetic field lines at the leading edge, thereby triggering reconnection. Concurrently, within the reconnection region, we observed distinct electron acceleration and heating signatures, including enhanced plasma flow, increased energy flux, and Joule dissipation. The electron characteristics exhibited significant differences between the two sides within the current sheet: on the left, the high-energy electron energy flux spectrum and pitch angle enhancements appeared only in the anti-parallel direction, whereas on the right, enhancements were observed in both parallel and anti-parallel directions. Furthermore, the electron velocity distribution function aligns with the distribution of local trapping mechanisms. These results suggest the potential existence of two different electron acceleration mechanisms during reconnection. This study reveals the coupling properties between high-speed jets and magnetosheath reconnection, providing new observational evidence for understanding how high-speed jets act as energy drivers influencing the energy transport and conversion in the magnetosheath.