Search

The spectral characteristics of the ULF waves (1mHz -1Hz) provide useful information about the conditions in the solar wind and in the magnetosphere. A series of geomagnetic field variations data are collected by the tri-axial search-coil instrument and acquisition system located at Panagjuriste, Geomagnetic Observatory (PAG), Bulgaria and other series of data are collected from two different instruments located at Conrad Observatory (WIC), Austria and Ebro Observatory (EBR), Spain, which operate within INTERMAGNET - the global network of geomagnetic observatories. We analyze the time series corresponding to the period 00 - 01 UT (02-03 LT) on 29 December 2020. To determine the spectral characteristics of observed geomagnetic pulsations, we apply the autocorrelation analysis to obtain the autocorrelation function and the power spectra, as well as Morlet wavelet analysis of the considered time series. Pulsations with an amplitude modulation period of about 15 min. (~900 s.) and main periods at 84, 75 and 68 seconds are determined. The specific spectral characteristics of these pulsations are obtained on the basis of the Morlet dynamic spectra. They show continuous ULF pulsations represented in four wave “packets” of sinusoidal oscillations with varying periods from 30 seconds till 115 seconds and main periods at 84 s., 75 s. and 68 seconds. We conclude that the recorded pulsations at Geomagnetic Observatory Panagjuriste, Bulgaria, located at mid latitudes, on 29 December 2020 during the time interval 00-01 UT are continuous ULF pulsations within the range Pc4 (45-150 seconds). Similar ULF continuous pulsations in the Pc4 range, with similar power spectra during the same time are observed both at Ebro and Conrad Observatories. [ABSTRACT FROM AUTHOR]