Systematic Evaluation of Low‐Frequency Hiss and Energetic Electron Injections

Abstract

The excitation of low‐frequency (LF) plasmaspheric hiss, over the frequency range from 20 Hz to 100 Hz, is systematically investigated by comparing the hiss wave properties with electron injections at energies from tens of keV to several hundreds of keV. Both particle and wave data from the Van Allen Probes during the period from September 2012 to June 2016 are used in the present study. Our results demonstrate that the intensity of LF hiss has a clear day‐night asymmetry, and increases with increasing geomagnetic activity, similar to the behavior of normal hiss (approximately hundred of hertz to several kilohertz). The occurrence rate of LF hiss in association with electron injections is up to 80% in the outer plasmasphere (L > 4) on the dayside, and the strong correlation extends to lower L shells for more active times. In contrast, at lower L shells (L < 3.5), LF hiss is seldom associated with electron injections. The LF hiss with Poynting flux directed away from the equator is dominant at higher magnetic latitudes and higher L shells, suggesting a local amplification of LF hiss in the outer plasmasphere. The averaged electron fluxes are larger at higher L shells, where significant LF hiss wave events are observed. Our study suggests the importance of electron injections and their drift trajectories toward the dayside plasmasphere in locally amplifying the LF hiss waves detected by the Van Allen Probes.

Statistical Properties of Hiss in Plasmaspheric Plumes and Associated Scattering Losses of Radiation Belt Electrons

“…However, some extreme events, such as large-amplitude or extremely low frequency ones in plasmaspheric plumes which are identified using the high-resolution waveform data (e.g., Su et al, 2018aSu et al, , 2018b, may be possibly underestimated in our study. In the previous work of Shi et al (2017), low-frequency hiss waves are found to occur more likely at higher L-shells, which may help explain the difference of hiss spectral intensity profile at L = 4.5 from the other three higher L-shells, while the similarity of the averaged hiss spectral intensities for L = 5.0,5.5,and 6.0 at the low-frequency end (Figure 4a) and the relatively small value of averaged B w at L = 5.5 (Figure 4b) remains unclear and is left for future investigation. In addition, we note that while the present study focuses on the statistically average properties of plume hiss and associated electron scattering effects in the quasi-linear regime, there is the possibility that the nonlinear scattering of electrons can be triggered by large-amplitude hiss waves (e.g., Su et al, 2018aSu et al, , 2018b, which also requires future investigation.…”

Particle Dynamics in the Earth's Radiation Belts: Review of Current Research and Open Questions

“…Due to their great contribution to particle scattering, the statistical distribution of hiss wave properties needs to be well characterized in magnetic local time (MLT), L‐shell, and geomagnetic activity. The most recent distributions available are the those generated by Li et al (), Malaspina et al (), Hartley, Kletzing, Santolik et al (), and Shi et al (, ) based on the Van Allen Probes, Tsurutani et al () based on Polar, Kim et al () based on THEMIS, and Meredith et al () based on DE1, Cluster, THEMIS, and the Van Allen Probes. An MLT‐dependent model of hiss amplitude is given in Spasojevic et al ().…”

Properties of Whistler Mode Waves in Earth's Plasmasphere and Plumes

“…The satellite was in the afternoon sector (MLT over 13.4-18.7) from 8:00 to 14:00 UT. The intensification of the observed hiss emissions is associated with injected anisotropic electrons(Figures 2f and 2g) probably due to local amplification(Shi et al, 2017) at higher L shells (L > 5.5). The anisotropy is calculated following equation (2) of M. W Chen et al (1999)…”