On the nature of Pc3 pulsations at L = 4 and their solar wind dependence

The results are presented of a statistical study of the occurrence, strength, frequency and polarization characteristics of magnetic pulsations in the Pc3 frequency range (0.022–0.1 Hz) recorded at Halley, L = 4, during September 1988. Similarities in the wave characteristics inside and outside the plasmasphere, suggest that many of the pulsations are due to forcing fast-mode waves. A correlative study with satellite measurements of the solar wind indicates a clear dependence of the occurrence and frequency of the pulsations, on the direction and magnitude of the interplanetary magnetic field, respectively. This is consistent with the hypothesis that the source of the pulsations seen on the ground is ion-cyclotron waves generated upstream of the Earth's bow shock and is direct evidence for the transference of energy from the solar wind to the ground in the form of hydromagnetic waves.