The two classes of whistler mode waves (chorus and hiss) play different roles in the dynamics of radiation belt energetic electrons. Chorus can efficiently accelerate energetic electrons, and hiss is responsible for the loss of energetic electrons. Previous studies have proposed that chorus is the source of plasmaspheric hiss, but this still requires an observational confirmation because the previously observed chorus and hiss emissions were not in the same frequency range in the same time. Here we report simultaneous observations form Van Allen Probes that chorus and hiss emissions occurred in the same range ∼300–1500 Hz with the peak wave power density about 10−5 nT2/Hz during a weak storm on 3 July 2014. Chorus emissions propagate in a broad region outside the plasmapause. Meanwhile, hiss emissions are confined inside the plasmasphere, with a higher intensity and a broader area at a lower frequency. A sum of bi-Maxwellian distribution is used to model the observed anisotropic electron distributions and to evaluate the instability of waves. A three-dimensional ray tracing simulation shows that a portion of chorus emission outside the plasmasphere can propagate into the plasmasphere and evolve into plasmaspheric hiss. Moreover, hiss waves below 1 kHz are more intense and propagate over a broader area than those above 1 kHz, consistent with the observation. The current results can explain distributions of the observed hiss emission and provide a further support for the mechanism of evolution of chorus into hiss emissions.
Bibliographical noteFunding Information:
This work is supported by the National Natural Science Foundation of China grants 41531072, 41274165, and 41404130. All the Van Allen Probes data are publicly available at https://emfisis.physics.uiowa.edu/data/index by the EMFISIS suite and at http://www.rbsp-ect.lanl.gov/data_pub/ by the HOPE and MagEIS instruments. The OMNI data are obtained from http://omniweb.gsfc.nasa.gov/form/dx1.html. This work was also supported from JHU/APL contract 921647 and 967399 under NASA Prime contract NAS5-01072.
©2016. American Geophysical Union. All Rights Reserved.
- RBSP results
- chorus waves
- plasmaspheric hiss