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CONSIDERATIONS ABOUT PROCEDURES FOR PROCESSING AND ANALYSIS OF GEOMAGNETIC DATA RECORDED IN OBSERVATORY
Abstract
Geomagnetic data used for the study of the large periodicities of the geomagnetic field are presented as a series of hourly averages covering two solar cycles. These data were downloaded from the ftp site of the World Data Center for Geomagnetism from Kyoto. These data were calculated annually based on final data both from analogue magnetograms and digital recordings. To study the diurnal variations, non-periodic variations (geomagnetic storms, phenomena SSC or SFE) were used as one-minute averages, recorded in Surlari Observatory. In order to study periodic phenomena with higher frequencies, we used values of the records of geomagnetic field components made with a sampling rate of 2 Hz, generally covering periods up to 24 hours. The first processing was performed on a series of hourly values, based on final data from Surlari geomagnetic observatory. We will illustrate, in the paper, the spectral processing of the data for a long information series, almost continuous as a series of average hourly values, calculated annually based on final data. At the latitude of the Surlari Observatory the horizontal component H has the highest degree of disturbance, reaching its variation amplitude of about 400 nT. The first stage of the data processing is the linearization process. After applying linearization characteristic equations for each component was obtained extracting of the secular variation of the geomagnetic field component and is preserved the effect of external geomagnetic field. We performed a Fourier analysis to view the predominant frequencies for each geomagnetic component and can be distinguished frequencies in the range 0.02 Hz - 0.1 Hz, so in this example pulsations have periods between 10 and 50 seconds, fits in Pc3 and Pc4 categories. Also, we presented a variation of amplitudes for different geomagnetic components. Thus, the horizontal components were recorded amplitudes up to 20-22 nT, while the vertical component amplitudes of 10-12 nT occurred and total geomagnetic field amplitudes were observed only 1-2 nT.Predominant frequencies of these pulsations were different depending on the analyzed component.
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