Open Access

Double-frequency oscillations of low energy plasma associated with transverse Pc 5 pulsations: GEOTAIL satellite observations

  • Tohru Sakurai1Email author,
  • Yutaka Tonegawa1,
  • Takuya Kitagawa1,
  • Motoharu Nowada1,
  • Ayako Yamawaki1,
  • Toshifumi Mukai2,
  • Susumu Kokubun3,
  • Tatsundo Yamamoto2 and
  • Koichiro Tsuruda2
Earth, Planets and Space201451:BF03352208

Received: 9 December 1997

Accepted: 16 October 1998

Published: 6 June 2014


The GEOTAIL satellite observed an interesting oscillation phenomenon of low energy plasma (LEP) in the dawnside outer magnetosphere. The oscillation was taking place with a frequency double that of the transverse oscillation of Pc 5 pulsations. The double-frequency oscillation appeared in the plasma density and temperature, clearly showing an out-of-phase relationship between them. However, this phenomenon is revealed to be an instrumental effect of the LEP detector, which has a low energy threshold of measuring an ion population at 32 eV/Q. The imbedded ion population is found to be composed of cold ions with an energy of less than the threshold. They are convected past the LEP detector by the Pc 5 wave and enter the detector energy window twice per wave period. Plasma bulk parameters calculated using the detected ions produce an oscillation that has a frequency exactly double that of the Pc 5 wave. However, it should be noted that this phenomenon is observed with a large amplitude electric field oscillation only in intervals when the satellite passes through the dawnside outer magnetosphere under very quiet magnetic conditions, i.e., periods of the northward interplanetary magnetic field.