Hiss Wave Evolution During Substorms Based on Van Allen Probes Observations

Hiss waves frequently occur in the plasmasphere or plumes, playing a key role in energetic electron loss in the Earth's inner magnetosphere. While previous studies have linked hiss wave enhancements in the outer plasmasphere (just inside the plasmapause) to electron injections during substorms, their evolution across various substorm phases remains unclear. Using Van Allen Probes observations over 2013–2019, we evaluate hiss wave evolution during various phases of substorm activity. At L > 4, both hiss wave intensity and energetic electron flux increase shortly after substorm onset, first on the morning side, then progress to later magnetic local times (MLTs) at a rate of ∼1–3 hr MLT per hr in universal time (UT), eventually stabilizing near 13 MLT. Stronger substorms result in larger and faster intensification in hiss wave intensity and have more significant impact at lower L-shells. Our results highlight the global variation of hiss waves during substorms.