A Systematic Study in Characteristics of Lower Band Rising-Tone Chorus Elements

Jih Hong Shue, Yasuhiro Nariyuki, Yuto Katoh, Shinji Saito, Yoshiya Kasahara, Yi Kai Hsieh, Shoya Matsuda, Yoshitaka Goto

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Chorus waves are usually generated outside the plasmapause in the equatorial region of the magnetosphere. The discrete characteristics of chorus elements are quantified by the three parameters: lasting time, frequency bandwidth, and repetition period. A systematic study in the lasting time and frequency bandwidth in terms of background plasma and magnetic fields has not been performed in the past. Here we use burst mode waveform data from the Time History of Events and Macroscale Interaction during Substorms (THEMIS) probes and the random forest method of machine learning and Pearson's correlation analysis to investigate which background plasma and magnetic field parameter is dominant over the lasting time and frequency bandwidth. We find that the temperature is the most important parameter that controls the lasting time. The lasting time is shorter when this temperature is higher. We also find that the normalized bandwidth by the local electron cyclotron frequency is controlled by the number density of energetic electrons. The normalized bandwidth is wider when this number density is larger. These results can be well explained by the threshold and optimum wave amplitudes for the nonlinear generation of chorus waves (Omura & Nunn, 2011, https://doi.org/10.1029/2010JA016280). The findings derived from this analysis can be used to serve as a guideline for a deep understanding of the generation mechanism of chorus elements and help choose input for a modeling of wave-particle interactions in the radiation belts.

Original languageEnglish
Pages (from-to)9003-9016
Number of pages14
JournalJournal of Geophysical Research: Space Physics
Issue number11
StatePublished - 1 Nov 2019


  • chorus waves
  • energetic particles
  • frequency shift
  • lasting time
  • temperature


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