THEMIS observation of chorus elements without a gap at half the gyrofrequency

S. Kurita, Y. Katoh, Y. Omura, V. Angelopoulos, C. M. Cully, O. Le Contel, H. Misawa

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)

Abstract

Using waveform data obtained by one of the THEMIS satellites, we report properties of rising tone chorus elements without a gap at half the gyrofrequency in a region close to the magnetic equator. The wave normal angle of the chorus elements is typically field-aligned in the entire frequency range of both upper-band and lower-band chorus emissions. We find that the observed frequency sweep rates are consistent with the estimation based on the nonlinear wave growth theory of Omura et al. (2008). In addition, we compare the frequency profiles of the chorus wave amplitudes with those of the optimum and threshold wave amplitudes derived from the nonlinear wave growth theory for triggering rising tone chorus emissions. The results of the comparison show a reasonable agreement, indicating that rising tone chorus elements are continually generated through a triggering process which generates elements with the optimum amplitudes for nonlinear growth.

Original languageEnglish
Article numberA11223
JournalJournal of Geophysical Research: Space Physics
Volume117
Issue number11
DOIs
Publication statusPublished - 2012

ASJC Scopus subject areas

  • Space and Planetary Science
  • Geophysics

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