Energy modulations of magnetospheric ions induced by foreshock transient‐driven ultralow‐frequency waves

Although foreshock transients can generate strong magnetospheric Pc5 ultralow-frequency (ULF) waves, whether they can modulate the energy of magnetospheric ions is still poorly understood. In this study, we analyze the strong magnetospheric ion energy modulations in a foreshock transient event on October 30, 2008, based on the magnetospheric observations by the time history of events and macroscale interactions during substorms A and D in the prenoon sector. ULF wave-induced ExB drift accelerated the cold ions up to similar to 10 keV and the enhanced ion fluxes have wave-like patterns. There is another portion of enhanced ion fluxes from similar to 0.8 to similar to 10 keV but with strong energy dispersions in this event. By comparing the observations and the theoretical prediction, we for the first time found that the drift-bounce resonances played a major role in modulating the energy of those ions with energy dispersions, during the interactions between the ions and the foreshock transient-driven Pc5 ULF wave with growing and damping effects.