AbstractTo examine the species dependence of the sustained energy spectrum gaps, in this letter, we analyzed the magnetic local time distribution of sustained proton and oxygen gaps and find that there is a clear difference between proton and oxygen ions: proton sustained gaps are predominantly distributed near the prenoon sector, while oxygen sustained gaps are mostly in the afternoon sector with lower occurrence rate than that for protons. This is primarily due to the different charge exchange loss rates of protons and oxygen ions. This scenario is supported by particle‐tracing simulations, which reproduce most of the observed characteristics. Through model‐data comparison, we found that the spectral gaps at different local times are formed by two different types of mechanisms: (a) the gap is formed due to the extended drift time which is responsible for the gap appearing on the dayside for both proton and oxygen ions; (b) the gap is formed inside the Alfven layer, which accounts for the observed sustained gaps in proton energy spectrums but not in oxygen ions due to the different charge exchange losses at various energies on the preexisting ion populations that lie on closed drift paths. These findings may provide insight into our understanding of ion composition and possible wave generation in the inner magnetosphere.
