Statistical Study of Geomagnetic Disturbances at European Auroral and High Latitudes

Abstract

Statistical studies allow probability statements about the frequency of certain events. The occurrence of magnetic substorms and their activity have been described with the help of extreme value distributions in the last few decades using the auroral electrojet indices AE, AL and AU. In this work we examined the distribution of the IL index, derived from observations at stations of the IMAGE magnetometer network. The distributions of magnetic disturbances, based on IL, were studied separately in the morning (3–9 MLT), day (9–15 MLT), evening (15–21 MLT), and night (21–3 MLT) sectors. In addition, we used the values of the IL index calculated from the meridional chains in the auroral zone (PPN-SOR) and from the chain of stations at high latitudes (BJN-NAL). The histograms, the empirical cumulative distributions and the occurrence rates were computed. It was shown that the empirical distributions could be well approximated with exponential distributions. The distribution parameters were determined from the occurrence rates. Three classes were discovered, which differ significantly by the respective distribution parameters. Structural changes in the distributions were found in the morning sector at both auroral and high latitudes. The relationship between the occurrence rate of magnetic disturbances with IL < −1000 nT and the frequency of occurrence of geomagnetic induced currents was highlighted.