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

The GEOTAIL satellite observed an interesting oscillation phenomenon of low energy plasma (LEP) in the dawnside outer magnetosphere. The oscillation w as 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 betw een 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 detecte d ions produce an oscillation that has a frequency exactly double that of t he Pc 5 wave. However, it should be noted that this phenomenon is observed with a large amplitude electric field oscillation only in intervals when th e satellite passes through the dawnside outer magnetosphere under very quie t magnetic conditions, i.e., periods of the northward interplanetary magnet ic field.