Acceleration of Ions by the ULF Waves Driven by a Foreshock Transient

Abstract:

Ions can be energized in the coupled magnetospheric and ionospheric system through auroral heating, particle transportation, wave-particle interactions, etc. Previous studies have shown that ions can be accelerated with interplanetary-shock induced ULF waves. On the other hand, foreshock transients, such as HFAs (hot flow anomalies), foreshock cavities and foreshock cavities, can also generate strong magnetospheric ULF waves. However, whether the ions can be accelerated with foreshock disturbances is still poorly understood. In this presentation, we show a foreshock transient event, which generated strong Pc5 ULF waves in the outer magnetosphere. We found the ions were accelerated up to ~10 keV with the waves. The ULF wave electric field likely contributed to the ion acceleration up to ~ 3 keV but was limited to the higher energy accelerated ions. Those higher energy ions were associated with energy dispersion and correlated with the poloidal mode component of the ULF waves. It indicates that the ion acceleration was likely caused by the drift-bounce resonance. Furthermore, the dispersion became more significant as time increased. By comparing this characteristic to the theory prediction, we found that this time-dependent energy dispersion was likely caused by the damping effect of the foreshock-transient induced ULF wave.