Field-aligned currents induced by foreshock transients and their effects on ions and neutral particles

Field-aligned currents (FACs) can be generated in the magnetosphere due to dynamic pressure variations associated with foreshock transients. The mechanisms may include: a) compressions or rarefactions causing divergence or convergence of diamagnetic or inertial currents in the magnetosphere, and b) compressions or rarefactions exciting shear Alfvénic waves associated with FACs. However, whether these FACs can further affect ions and neutral particles in the coupled ionospheric-thermospheric system remains unclear.

In this study, we utilized coordinated observations from THEMIS probes, (near-)polar-orbiting satellites (DMSP and SWARM), and ground-based optical imaging to identify FACs induced by foreshock transients and investigate their effects on ions and neutral particles. Ground-based all-sky imagers show that foreshock transients can generate traveling convection vortices (TCV) auroras near the equatorial boundary of the auroral oval and field line resonance (FLR) arcs at relatively lower latitudes. Events with conjugate DMSP observations reveal that the corresponding upward FACs were associated with ionospheric ion outflows, Poynting fluxes, and low-energy electron precipitation. Events with conjugate SWARM and optical observations indicate that these FACs were also associated with neutral wind divergence at ~250 km and enhanced neutral density at SWARM altitudes. This suggests that energy heating from foreshock-induced FACs can cause neutral wind perturbations and elevate neutral particles to higher altitudes.