Geomagnetic and Telluric Field Variability as a Driver of Geomagnetically Induced Currents

We analyse temporal and spatial variability of geomagnetic and telluric electric fields in the Eastern Fennoscandia. These variations are compared with available geomagnetically induced current (GICs) measurements in electric power transmission lines at Kola Peninsula and Karelia. The information on impedance tensors is provided by the electromagnetic sounding array BEAR. We synthesize the telluric E-field from geomagnetic field variations, using the complex impedance tensor. We analyze geomagnetic and E-field variations at several sites for different space weather events: magnetic storm and Pi3 pulsations. We compare the spectral content of geomagnetic, telluric, and GIC variations. This comparison shows that the commonly used as a measure of GIC disturbances time derivative of geomagnetic field dB/dt does not totally control them. The suppression of high-frequency component in the GIC spectrum as compared with dB/dt variations is determined by the frequency-dependent character of the crustal geoelectric response.