Pc5 pulsations observed in the dayside magnetosphere by Geotail

The Geotail spacecraft remained close to the dayside magnetopause from October 17 to October 18, 1992. During the intervals of this very unique orbit when the spacecraft was within the magnetopause, Pc5 pulsations were observed almost continuously in the magnetic field and in the electric field. The signature of the pulsations agrees with the theory of field line standing oscillations with the mode being the fundamental. The observed Pc5 pulsations were regarded to be triggered by sudden compressions and expansions of the magnetic field. The resulted displacement of the field line reached a maximum of 2Re.