## 5 Map of Telluric Field Response to a Geomagnetic Disturbance over Northern Russia  
For qualitative operative estimates of expected vulnerability of a technological system to geomagnetic variations, it is desirable to have a map with the telluric response amplitude to a given disturbance of the magnetic field. A map, similar to [2], but for the territory of the Russian Federation, was constructed here. The map is based on the geoelectric model [30]. The spatial distribution of the average conductivity in the upper 10 km layer of the Earth's crust derived from this model for the territory of the Russian Federation is shown in Figure 9. The lowest conductivities, \(\sim\)10\({}^{-5}\)-10\({}^{-4}\) S/m, correspond to the Precambrian basement outcrops (Fennoscandian Shield) and to the exposed nuclei of the Paleozoic and Mesozoic orogenic structures: Kola Peninsula, Karelia, Urals, Novaya Zemlya, Taimyr, and Chukotka. In the Yamal region covered by thick Mesozoic sedimentary cover, the conductivity is generally quite high. The spatial distribution of the electric field response to geomagnetic disturbance was calculated from the corresponding impedances using harmonic approximations of geomagnetic disturbances. The simplest approximation of the driving magnetic field was taken in the form of a plane wave with an amplitude of 1 nT and oscillating with a fixed  
Figure 8: Schematic illustration of the formation of GIC-effective frequency interval in the spectral content of geomagnetic variations. Figure 9: Map of the spatial distribution of the average conductivity\(\sigma\) [S/m] in the upper 10 km of the conductivity model [30] in the territory of the Russian Federation. frequency. The magnetic variations were assumed to be in the longitudinal direction, though for the considered 1-D algorithm of the telluric electric field calculation, the actual polarization is not important. The calculation of the electric field according to the available MT impedance was performed on a 0.25\({}^{\circ}\)\(\times\) 0.25\({}^{\circ}\) grid using local vertical profiles of conductivity in each node from the model [30]. The calculated spectral amplitudes were multiplied by the spectral width to obtain the amplitude (in mV/km) of the excited telluric field. The examples given above indicate that the most intense GICs are provided by geomagnetic pulsations with time scales of about 100-1000 s, so these periods were chosen for modeling. Figure 10 shows a map of the magnitude of synthetic geoelectric fields that could be excited by spatially homogeneous magnetic field variations with \(T\) = 100 s throughout the territory of the Russian Federation. According to this \"telluric hazard\" map, the highest values of geomagnetically induced fields up to \(E_{\mathrm{H}}\) \(\sim\) 5 mV/km (normalized to the exciting magnetic field) are typical for the northwest of the Russian Federation. In this region, the magnitudes of the telluric field for different points can differ 3-4 times under the same amplitudes of the magnetic disturbance. In addition, increased values should occur in the Urals. In the Yamal region, the telluric fields are weak, \(\sim\)0.5 mV/km. A similar map, but for the driving magnetic disturbance with \(T\) = 1000 s, is shown in Figure 11. It demonstrates that a lower-frequency variation excites a lower amplitude of telluric currents. The maps in Figures 9-11 prove that the geological structure significantly affects the amplitude of geoelectric fields generated by magnetic disturbance. The constructed map of normalized amplitudes of geoelectric responses to external plane-wave geomagnetic excitation provides helpful information for system operators in regard to space weather disturbances. Figure 10: Map of the horizontal geoelectric field magnitude \(\mid E_{\mathrm{H}}\mid\), excited by uniform magnetic field variations with period \(T\) = 100 s and magnitude 1 nT. The horizontal scale of even localized magnetospheric disturbances on the ground (such as magnetic impulses composing Pi3/Ps6 pulsations) is about 200-300 km.