Space-Weather-Driven Geomagnetic- and Telluric-Field Variability in Northwestern Russia in Correlation with Geoelectrical Structure and Currents Induced in Electric-Power Grids

The study results of the temporal and spatial variability of geomagnetic and telluric fields driven by anomalous space weather are presented for the central and eastern parts of the Fennoscandian shield. Data from the Scandinavian network of geomagnetic observations IMAGE are analyzed together with the measurements of the geomagnetically induced currents (GIC) in nearby electric power lines of Karelia and the Kola Peninsula, as well as synthesized telluric fields. To synthesize telluric fields from the observed geomagnetic variations, we use magnetotelluric impedance estimates obtained during the BEAR electromagnetic sounding experiment in Fennoscandia. A comparison of the spectral composition of geomagnetic, telluric, and GIC variations in various sites and for various space weather events has shown that time derivative of the geomagnetic field (dB/dt), which is commonly used as a measure of GIC disturbances, does not fully control the latter. The analyzed telluric fields and observed GICs demonstrate a significant dependence on the induction response of the electrically conducting Earth interiors, the character of which varies greatly in different geological domains of the Fennoscandian shield. The regional spatial variations in the telluric field and GICs caused by the geoelectric structure heterogeneity are superimposed on the regular decreasing trend in their amplitudes with increasing distance from auroral latitudes. Based on magnetotelluric sounding data, estimates of the extreme values of telluric fields during geomagnetic storms and substorms are obtained for different sites, which is the key information for predicting GICs in regional power lines.