Research On The Spectral Characteristics Of Geomagnetically Induced Currents And Its Driving Source Based On Geomagnetic Storm

The high-speed and high-energy solar wind ejected by solar activities spreads to the earth space,which can cause severe geomagnetic disturbances(such as auroral substorms,geomagnetic storms,etc.).Geomagnetically induced currents will be formed in the transmission line and its closed loop with the earth conductor.GIC flows into the grid,which can cause half-wave saturation,harmonics and reactive power loss of the transformer to increase.And then,the voltage fluctuation of the entire power system is caused,which endangers the stable operation of the power grid.This paper mainly studies the GIC caused by geomagnetic storms,and analyzes the characteristics of GIC caused by different levels of geomagnetic storms.Exploring GIC signatures caused by interplanetary actuation of non-reproducible geomagnetic storms.Firstly,all geomagnetic storm events with moderate intensity(Dst≤-50 nT)during 1999-2020 were screened out using the Dst index.And it is classified into four levels:moderate magnetic storm,large magnetic storm,ultra magnetic storm,and super magnetic storm.By analyzing the interplanetary magnetic field,solar wind parameters and geomagnetic conditions of different levels of magnetic storms,the characteristics of GIC and their dependencies are explored.It is found that GIC is related to the Bz component of the interplanetary magnetic field,magnetic storms,and substorms.The characteristics of GIC in geomagnetic storms are counted,and it is found that the Dst index has a good correlation with the absolute value of GIC.By analyzing GIC storms,it is found that GIC storms may also be triggered in smaller-scale magnetic storms.GICs are not only related to the interplanetary magnetic field conditions,but also affected by the local space current system.Secondly,the wavelet transform method is used to analyze the spectral characteristics of GIC,and to explore its correlation with dBx/dt.Through Continuous Wavelet Transform(CWT)and Discrete Wavelet Transform(DWT),the spectral characteristics and wavelet coefficient characteristics of GIC in different levels of magnetic storm events are analyzed.It is found that the energy distribution and periodic characteristics of GIC and dBx/dt in the frequency domain of different levels of magnetic storms are similar,and both have obvious low-frequency characteristics.The correlation and phase characteristics of GIC and dBx/dt in high and low energy regions were simultaneously analyzed by Cross Wavelet Transform(XWT)and Wavelet Coherence(WTC).It is found that GIC and dBx/dt have a large correlation in both high-energy and low-energy regions,and there is a certain positive correlation between them.Finally,according to the different structural types of the interplanetary drive-Interplanetary Coronal Mass Ejection(ICME)causing non-reproducible geomagnetic storms:Independent ICME(I-ICME),Multiple ICMEs(M-ICME),Shock ICMEs(S-ICME),which analyzes the induced GIC and its spectral characteristics.The study found that the GIC induced by I-ICME had the characteristics of concentration,and there were two obvious disturbances in the GIC induced by M-ICME and S-ICME,but the first disturbance of the GIC induced by S-ICME was short in duration.GIC has a great correlation with the total interplanetary magnetic field B and the southward component of the interplanetary magnetic field Bz.Statistics of three types of ICME events showed that I-ICME and S-ICME mainly caused small-intensity GIC events,and M-ICME had a higher probability of triggering larger-intensity GIC events.The energy distribution characteristics of different types of ICME-induced GIC were analyzed by CWT.It was found that GIC presented one high-energy region under the condition of I-ICME,while M-ICME and S-ICME presented two high-energy regions with differences in energy intensity.In summary,this paper traces the source of GIC events upward,and analyzes the characteristics of GIC in different levels of geomagnetic storms and different types of ICMEs.Research on the spectral characteristics of GIC based on geomagnetic storms and their interplanetary driving will help to clarify the relationship between GIC and its driving source.It provides a physical basis for the modeling and forecasting of GIC storms,and has important research value on the impact of space weather prevention and control in power systems.