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.


Plasma SheetVelocity Distribution FunctionMagnetic Local TimeEnergy PlasmaLarge Amplitude Oscillation