Dependence of Low-Frequency Plasmaspheric Hiss on Geomagnetic Activity and Solar Wind Dynamic Pressure and Its Electron Scattering Effects

Abstract

Plasmaspheric hiss plays a crucial role in shaping the structure and dynamics of Earth's radiation belts. It's also recognized that low-frequency hiss has characteristics and excitation mechanisms quite different from those of typical normal-frequency hiss. Using high-quality data from Van Allen Probe A between September 2012 and March 2019, we conduct a comprehensive statistical analysis of the global distribution of low-frequency hiss. We investigate the global morphology of low-frequency hiss concerning different conditions of geomagnetic activity and solar wind dynamic pressure (P_dyn). The results reveal significant differences in the global distributions of wave amplitude and occurrence rate between low-frequency hiss and broad-band hiss, particularly in their L-shell distributions. Large-amplitude low-frequency hiss is primarily observed on the afternoon side with L > 5 shifting toward the noonside as the geomagnetic activity intensifies. Furthermore, both the amplitude and occurrence rate of low-frequency hiss decrease with increasing P_dyn, and the occurrence rate exhibits a north-south asymmetry with strong P_dyn. The spectral analysis indicates that the peak frequency of the low-frequency hiss is ∼50 Hz, remaining almost constant with increasing L-shell. Evaluations of hiss-induced electron scattering effects show that the electron resonant energies and scattering rates by low-frequency hiss are significantly different from those by broad-band hiss. Low-frequency hiss has a higher minimum electron resonance energy and larger scattering rates over most of the pitch angle range. Our results are valuable in complementing the existing global distribution model of plasmaspheric hiss and providing an improved understanding of its essential contributions to the radiation belt electron dynamics.