On the origin of a burst of unstructured Pel pulsations according to simultaneous observations from the ground and geostationary orbit

We examined the features of bursts of unstructured Pc1 geomagnetic pulsations in the range of periods (7=2÷5 s), based on simultaneous observations by geostationary satellites GOES-10, 11, 12, and by ground-based magnetometer network CARISMA. The excitation of pulses was due to the contact of the magnetosphere with the interplanetary shock wave (ISW) on 19 November 2007. We detected the eastward drift of the source of unstructured Pc1 bursts in the geostationary orbit: the burst was first observed by GOES-11 (MLT~09 h), then by GOES-12 (MLT~13 h) and, finally, by GOES-10 (MLT~14 h). At the ground-based observatories with the longitudinal distance of ~40° between them, the oscillation onset delayed in the west and east observatories as compared to the median Fort Simpson Observatory. On the sharp leading edge of oscillations, we observed an increase in the frequency that lasted for about 150 seconds from the minimum to maximum values. We determined the velocity of travel of the pulsation source from the difference between the moments when pulsations were first recorded on the satellites and on the Earth. To interpret the observed patterns of pulsation, we considered three alternative models: 1. Generation of pulsations as a result of eastward drifting clouds of energetic electrons accelerated due to the compression of the magnetosphere. 2. Generation of pulsations in the plasmaspheric bulges (or detached ducts). 3. Modulation of the generation conditions of pulsations by the surface wave which propagates along the magnetopause and is generated in the ISW/magnetopause contact region.