Competitive Influences of Different Plasma Waves on the Pitch Angle Distribution of Energetic Electrons Inside and Outside Plasmasphere

By analyzing the Van Allen Probe B observations and 2-D simulations, we found that the competitive influences of different plasma waves on the pitch angle distribution of energetic electrons (hundreds of keV) depend on density of ambient plasmas and relative intensity of waves. In the high-density plasmasphere (>70 cm⁻³), plasmaspheric hiss is able to effectively remove small pitch angle electrons (<60°), while the participation of intense magnetosonic (MS) waves merely increases part of large pitch angle electrons (>60°). The combined diffusions by the two waves create pancake-like electron pitch angle distributions in the high-density region. Outside the plasmapause, the same-intensity MS waves and weak exohiss waves mainly reduce large pitch angle electrons and thus create butterfly-like pitch angle distributions in the low-density trough (<70 cm⁻³). These results indicate that energetic electrons could have different pitch angle distributions under similar wave environments but different plasma densities.