ИСТИНА

The rapid changes of magnetic fields, that is high dB/dt, associated with substorms can excite large geomagnetically-induced currents (GICs) that can have harmful effects on technological systems. We have analyzed the characteristics of enhancements of dB/dt observed in Fennoscandia in 2015 using data from the magnetometer array IMAGE, covering a range of magnetic latitudes from 68° to 78°. The abrupt magnetic field variations may be associated with substorm onsets, isolated nightside magnetic impulsive events (MIEs) with ~10 min duration, and Ps6/Pc5 pulsations (periods 5-15 min). For a detailed examination of the latitudinal structure of magnetic variability enhancements and their association with auroral oval boundaries we applied the technique of “magnetic keograms”. This technique is simple enough for mass-processing and helps to visualize and characterize the fine structure of a substorm, namely the time and latitudinal localization of dB/dt enhancements. The proposed technique of the dB/dt keograms could be an efficient method revealing the latitudinal localization of magnetic variability and its time evolution following substorm expansion phase onset. A location of the auroral oval boundaries in a given local time sector has been estimated with the OVATION-prime model based on energetic particle measurements from the DMSP satellites. Different types of impulsive disturbances provided enhancement of dB/dt with different magnitudes, but mostly exceeding the commonly used threshold of 5 nT/s for potential damage to the electrical grid. Auroral substorm onset provided the largest magnetic response on the ground and most intense GIC (few tens of A) when the poleward moving intensification of dB/dt crossed the latitude of power line. Polar substorms originating at much higher latitudes are less effective in GIC excitation, ~6 A only. Isolated nightside MIEs are also effective in excitation of GICs (>10 A), but they are relatively rare. Quasi-periodic series of MIEs, known as Ps6 / Pi3 pulsations, are effective in excitation of GICs with magnitude about 20 A and even higher. Monochromatic Pc5 pulsations are capable to induce noticeable GICs, up to ~13 A.