The Spatio-Temporal Features of Pc1 Structured Geomagnetic Pulsations

The results of a study of the spatio-temporal features and interplanetary conditions for the excitation of structured geomagnetic pulsations in the range Pc1 ("pearls") are presented. For the analysis, we used simultaneous dynamic spectra of ultra-low-frequency oscillations in the frequency range 0.2-5.0 Hz obtained from digital data with high resolution of synchronous observations at two mid-latitude Borok observatories (BOX, phi' = 53.6 degrees; ?' = 114.4 degrees; L = 2.8) and Mondy (MND, phi' = 47 degrees; ?' = 174 degrees; L = 2.1) for the period from 1996 to 2001. During the analyzed period, 108 coherent series of "pearls" were selected at two observatories. It was found that the series of Pc1 pulsations were observed at the Borok observatory in relation to the Mondy observatory simultaneously (19% of cases), later (54% of cases), and earlier (27% of cases). It is shown that the time intervals of the effects of later arrival and advance of the onset of pearls in BOX with respect to MND were predominantly 10 and 20 min, respectively. Significant differences were found in the diurnal variation in the number of cases of Pc1 pulsations and geophysical conditions under which the Pc1 series are excited simultaneously, or later or earlier to BOX in relation to MND. The detected effects of western and eastern drift of the Pc1 series may be due to the position of the oscillation source relative to the plasmapause, depending on the interplanetary conditions.