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Electrostatic quasi-monochromatic waves in the downstream region of the Earth’s bow shock based on Geotail observations


Geotail plasma wave observations show the existence of intense electrostatic quasi-monochromatic (EQM) waves in the downstream region of the Earth’s bow shock. They oscillate parallel to the ambient magnetic field and appear at frequencies between the electron plasma and ion plasma frequencies. Although these waves have been believed to be Doppler-shifted ion acoustic waves, the typical plasma parameters observed in the downstream region do not support the generation conditions for ion acoustic waves. In this paper, the existence of cold electron beam-like components accompanying EQM waves is considered based on waveform and statistical analyses. Linear dispersion analyses using realistic plasma parameters revealed that the cold electron beams cause destabilization of electron acoustic waves at frequencies consistent with those of observed EQM waves. The results of observations and linear analyses suggest that EQM waves are generated by the destabilization of the electron acoustic mode.


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Correspondence to Koichi Shin.

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Shin, K., Kojima, H., Matsumoto, H. et al. Electrostatic quasi-monochromatic waves in the downstream region of the Earth’s bow shock based on Geotail observations. Earth Planet Sp 59, 107–112 (2007).

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Key words

  • Electrostatic plasma wave
  • electron acoustic mode
  • downstream region of the bow shock