MLT-dependence of sustained spectral gaps of proton and oxygen in the inner magnetosphere

Yue et al. (2021) have investigated the characteristics of oxygen sustained gaps. In order to examine the species dependence of the sustained gaps, in this letter, we further analyzed the MLT distribution of sustained proton gaps and find that there is clear difference between proton and oxygen ions: proton sustained gaps are predominantly distributed near the pre-noon 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.