Spectral analysis of geomagnetically induced current and local magnetic field during the 17 March 2013 geomagnetic storm

Abstract

Geomagnetically induced current (GIC) is known to be closely related to the rate of change of local horizontal magnetic field (dBx/dt); and their spectra can give better insight into the relationship. We study the spectral characteristics of GIC measured in Finland and dBx/dt measured 30 km away during the 17 March 2013 intense geomagnetic storm (SymHMin = -132 nT). Two bursts of large GIC (up to 32A) and dBx/dt occurred at ~ 16 UT and 18 UT during the storm main phase, though their values were generally small. For the first time, the Cross Wavelet Transform (XWT) and Wavelet Coherence (WTC) techniques are used to investigate the correlation and phase relationship of GIC and dBx/dt in time-frequency domain. Their WTC correlation is strong (over 0.9) over the entire storm period, indicating dBx/dt is the main factor causing GIC and dBx/dt leading GIC. Their XWT spectra show two enclosed periods (8–42 min and 2–42 min) in the high energy region corresponding to the two bursts of activity in GIC and dBx/dt. Moreover, we use continuous wavelet transform (CWT) and discrete wavelet transform (DWT) to analyze the spectral characteristics of GIC and dBx/dt. It is found that the CWT and DWT spectra of the two are very similar, especially in the low frequency characteristics, without continuous periodicity. Wavelet coefficients become large when GIC and dBx/dT are large; and the third-order coefficient, which corresponds to low-frequency part, best reflects the disturbance of GIC and dBx/dt.

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“…Changes in the geo-electric field produce geomagnetically induced currents in the power grid system. Since the proposal and study of the impact of geomagnetic storms on the security of China's power grid in 2000 [5][6][7], the study has made significant progress. Influenced by the research results of countries at high latitudes, our scholars believe that countries at high latitudes are more susceptible to geomagnetic storms, and transmission lines oriented in the east-west direction are more susceptible than those oriented in the north-south direction [8][9], as in the case of the power outage in Quebec, Canada.…”