The Spatio-Temporal Features of Pc1 Structured Geomagnetic Pulsations

The results of a study of the spatio-temporal features and interplanetary conditions for the excitationof structured geomagnetic pulsations in the range Pc1 (“pearls”) are presented. For the analysis, weused simultaneous dynamic spectra of ultra-low-frequency oscillations in the frequency range 0.2–5.0 Hzobtained from digital data with high resolution of synchronous observations at two mid-latitude Borok observatories(BOX, Φ' = 53.6°; Λ' = 114.4°; L = 2.8) and Mondy (MND, Φ' = 47°; Λ' = 174°; L = 2.1) for theperiod from 1996 to 2001. During the analyzed period, 108 coherent series of “pearls” were selected at twoobservatories. It was found that the series of Pc1 pulsations were observed at the Borok observatory in relationto the Mondy observatory simultaneously (19% of cases), later (54% of cases), and earlier (27% of cases). Itis shown that the time intervals of the effects of later arrival and advance of the onset of pearls in BOX withrespect to MND were predominantly 10 and 20 min, respectively. Significant differences were found in thediurnal variation in the number of cases of Pc1 pulsations and geophysical conditions under which the Pc1series are excited simultaneously, or later or earlier to BOX in relation to MND. The detected effects of westernand 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