Plasma distribution functions in the Earth's magnetotail (XGSM∼ −42RE) at the time of a magnetospheric substorm: GEOTAIL/LEP observation

S. Machida, T. Mukai, Y. Saito, M. Hirahara, T. Obara, A. Nishida, T. Terasawa, K. Maezawa

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8 Citations (Scopus)


Three plasma burst events were observed with the Low Energy Particle (LEP) instrument onboard GEOTAIL at XGSM=−42 RE. Two of these events were detected when the spacecraft was in the plasma sheet. In these events, the first signature of the burst was the tailward flow of the accelerated electrons with energies of about 5 keV. This was followed by the appearance of the tailward streaming ions with energies > 20 keV. Importantly, these tailward streaming ions were observed together with the non‐streaming ions of the plasma sheet which had not experienced acceleration or heating. Then the electron distribution function started to develop an elongated core component at < 1 keV and isotropic or perpendicularly heated structure at > 1keV. These two events lasted for about two minutes. The spacecraft was in the tail lobe before the third event took place. In this event the first signature was the bistreaming electrons with peak energy at 2 keV. After a short interval of the flux decrease, hot electrons with energy ∼3 keV appeared. The velocity distribution function of the ions had an incomplete shell structure with an average tailward velocity of ∼900 km/sec. The non‐streaming component was absent in this case. It is suggested that in the first two events the spacecraft was in the plasma jet emanating from the near Earth neutral line, while it traversed the edge of the plasmoid in the third event. The associated substorm onset can be identified for the first event after which the disturbance continued.

Original languageEnglish
Pages (from-to)1027-1030
Number of pages4
JournalGeophysical Research Letters
Issue number11
Publication statusPublished - 1994 Jan 1
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)


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