Plumes of the plasmasphere and variations in the geomagnetic field horizontal component

The effects of the dayside and dusk plumes of the plasmasphere during the ring current recovery phase on the disturbance level of the ground geomagnetic field horizontal component have been considered. It has been indicated that the geomagnetic field horizontal component changes specifically and synchronously in the region corresponding to the plasmaspheric dayside plume. Outside the plume the time variations in the geomagnetic field horizontal component pronouncedly differs. A spectral analysis of disturbances in the geomagnetic field horizontal components in the range of geomagnetic pulsations indicated that the intensity in the range of Pc4 pulsations increases at magnetic stations located on field lines corresponding to the dayside and dusk plumes of the plasmasphere. These pulsations detected in the dynamic spectrum of the geomagnetic field horizontal components in the dayside plume region of the plasmasphere, probably reflect the resonance oscillations of magnetic field lines in the region of field-aligned currents at comparatively low altitudes. We assume that this is caused by the instability of field-aligned currents originating as a result of the interaction between the ring current energetic ions and electromagnetic waves in the region with a relatively dense background plasma of the dayside plume.