Magnetic reconnection and high-speed jets downstream of a parallel shock: Full PIC simulation

Magnetic reconnection is one of the most fundamental processes governing energy conversion and particle acceleration in collisionless space plasmas. Observations have revealed the occurrence of magnetic reconnection (Phan et al., 2018) and transient structures such as high-speed jets (HSJs; Hietala et al., 2009) in planetary magnetosheaths. Statistical studies based on Cluster and MMS measurements have shown that most HSJs are preferentially located downstream of the quasi-parallel bow shock (Escoubet et al., 2020). In recent years, global hybrid simulations have been extensively employed to investigate the three-dimensional global distribution of HSJs and their associated ion kinetic properties (Palmroth et al., 2021; Yang et al., 2023; Guo et al., 2024; Fatemi et al., 2024). In this study, we perform full particle-in-cell (PIC) simulations spanning spatial scales of several Earth radii and, for the first time, demonstrate an “all-in-one” multiscale kinetic scenario linking foreshock ultra low frequency (ULF) wave, non-stationary shock front (Lembege & Savoini, 1992), downstream high-speed jet (Hietala et al., 2009) and bow wave (Liu et al., 2020) formation, and the subsequent triggering of magnetic reconnections. The simulations illustrate how high dynamic-pressure structures embedded in foreshock low-frequency waves can traverse a self-reforming shock, in good agreement with MMS observations reported by Raptis et al. (2022). Furthermore, the spatial relationships among HSJs, turbulent filamentary current sheets, and reconnection sites are identified. Using the guiding-center framework commonly applied to adiabatic electron acceleration in reconnection, we quantify the relative contributions of parallel electric fields, betatron acceleration, and Fermi processes to electron energization at different stages of HSJ-driven reconnection evolution. Finally, based on our simulation results, we present a preparatory investigation for the upcoming SMILE mission (launch scheduled for 2026), discussing the penetration depth of HSJs and their induced magnetopause deformation, and providing corresponding soft X-ray images.