Physics of auroral phenomena : proceedings of the 40th annual seminar, Apatity, 13-17 March, 2017 / [ed. board: N. V. Semenova, A. G. Yahnin]. - Апатиты : Издательство Кольского научного центра РАН, 2017. - 143 с. : ил., табл.

The magneticfield variability and geomagnetically induced currents in electricpower lines The estimates of the correlation coefficients R between the GIC intensity and magnitudes of the geomagnetic field derivatives during the time intervals 07-10 UT gives the following results: fl(|dX/dt|-|IGic|)=0.45, K(|dY/dt|- |Igic|)=0.61, and J?(|dB/dt|-|IQic|)=0.63. Hence, the magnitude o f total derivative |dB/dt| correlates best with GIC variations, whereas the derivative of У-component even better correlates with GIC variations than the derivative o f X- component. The same regularities are observed for other time intervals. The application of the RB parameter (Fig. 5) to the data from IVA station evidences that during this geomagnetic storm geomagnetic field varies not only in magnitude, but in direction, too. Indeed, at this station, as well as at other IMAGE stations, RB rapidly increases from -0.6 to -1.0 during the periods of vortex-like ionospheric structures occurrence. Thus, such geomagnetic variations cannot be attributed to variations of the east-west auroral elecrojet intensity only. 5. Discussion. The GIC occurrence is often interpreted as a result of fluctuations o f auroral clectrojet, flowing mainly in the westward direction. Accordingly, for GIC modeling the model of extended east-west electric current has been used [Viljanen, 1997]. In accord with these models the conclusions have been stated that predominantly power systems elongated in longitudinal E-W direction are vulnerable to impact of geomagnetic storms and substorms. The vector technique used here has demonstrated a much larger variability o f dB/dt in magnitude and direction as compared with just magnetic variations AB. The applied quantitative estimate of vector field variability RB confirmed that geomagnetic field variations occur in a comparable rate both in magnitude and direction. These results indicate an importance of account of small-scale current structures embedded into global auroral electrojet for GIC estimates. The observed patterns of dB/dt distribution cannot be interpreted by a simple model of elongated electrojet and demands an account of magnetic field from nonstationary vortex-like structures, produced by localized field-aligned currents flowing in/out the ionosphere [Belakhovsky et al., 2017]. Though amplitudes of currents in such structures are not large, so they cannot modify essentially AB distribution, but their temporal variations are fast, so they influence substantially distribution of dB/dt. The physics and morphology of these small-scale fast-varying current filaments have not been established yet. Thus, though largest magnetic disturbances are produced by the auroral clectrojet and directed in north-south direction, rapid variations of geomagnetic field essential for the GIC excitation are considerably determined by small-scale current systems, which disturbed both horizontal components o f geomagnetic field. An evident confirmation of this fact is a noticeable vulnerability of Kola power lines extended in the north-south direction to GIC occurrence. 6. Conclusion. The large-scale structure of the ionosphere currents at auroral latitudes arc determined by the east- west electrojet. So, the X-component of the geomagnetic field is prevalence here. However, on small scales these equivalent currents and induced geomagnetic disturbances undergo strong variations not only in value but also in direction. So, the GIC are oriented as in east-west as in north-south direction. The vector technique o f the geomagnetic field and its derivate representation shows the greater variability of the dB/dt in comparison with AB. These results cannot be explained by the simple model of auroral electrojet and shows the importance o f the accounting of small- scale currents for the GIC calculations. Acknow ledgements. This study is supported by the Russian Foundation for Basic Research № 16-35-60049 m o l a d k (VB), № 15-45-05108 r_vostok_a (VAP). Data from PGI system are available at http://eurisgic.org. We acknowledge Finish Meteorological Institute for IMAGE magnetometer data ( http://www.geo.fmi.fi/image/) . References - Du J., Wang C., Zhang X.X., Shevyrcv N.N., Zastenker G.N. Magnetic field fluctuations in solar wind, foreshock and magnetosheath: Cluster data analysis // Chin. J. Space Sci., 2005, 25, 368-373. - Friis-Christensen E., M.A. McHenry, C.R. Clauer, Ionospheric traveling convection vortices observed near the polar cleft: A triggered response to sudden changes in the solar wind // Geophys. Res. Lett. 1988, 15, 253-256. - Lanzerotti L.J. Space weather effects on technologies // Space Weather, AGU. 2001. vol. 125, 11. - Belakhovsky V.B., Pilipenko V.A., Sakharov Ya.A., Selivanov V.N., Characteristics of the geomagnetic field variability for the study of magnetospheric storm and substorm impact on electric power systems // Solid Earth Physics (Fizika Zemli), 2017 (in press). - Piijola R., Kauristie K , Lappalainen H., Viljanen A., Pulkkinen A. Space weather risk // Space Weather. 2005, 3, S02A02. - Sakharov Ya.A., Kudryashova N.V., Danilin A.N., Ostafiychuk R.M., Saranskiy S.N., Geomagnetic disturbances and railway automatic failures // Proc. of 8th Intern. Symp. on Electromagnetic Compatibility and Electromagnetic Ecology, St-Ptb, 2009, 235-236. - Viljanen A. The relation between geomagnetic variations and their time derivatives and implications for estimation of induction risks // Geophys. Res. Lett. 1997. V. 24. 631 -634. 37