Measurement of geomagnetically induced current (GIC) around Tokyo, Japan

We need a typical method of directly measuring geomagnetically induced current (GIC) to compare data for estimating a potential risk of power grids caused by GIC. Here, we overview GIC measurement systems that have appeared in published papers, note necessary requirements, report on our equipment, and show several examples of our measurements in substations around Tokyo, Japan. Although they are located at middle latitudes, GICs associated with various geomagnetic disturbances are observed, such as storm sudden commencements (SSCs) or sudden impulses (SIs) caused by interplanetary shocks, geomagnetic storms including a storm caused by abrupt southward turning of strong interplanetary magnetic field (IMF) associated with a magnetic cloud, bay disturbances caused by high-latitude aurora activities, and geomagnetic variation caused by a solar flare called the solar flare effect (SFE). All these results suggest that GIC at middle latitudes is sensitive to the magnetospheric current (the magnetopause current, the ring current, and the field-aligned current) and also the ionospheric current.

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

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.

The Interplanetary and Magnetospheric Causes of Geomagnetically Induced Currents (GICs) > 10 A in the Mäntsälä Finland Pipeline: 1999 through 2019

The interplanetary and magnetospheric causes of intense geomagnetically induced current (GIC) > 10 A and > 30 A events during 21 years (1999 through 2019) at the Mäntsälä, Finland (57.9° magnetic latitude) gas pipeline have been studied. Although forward shocks and substorms are predominant causes of intense GICs, some newly discovered geoeffective interplanetary features are: solar wind plasma parcel (PP) impingements, possible interplanetary magnetic field (IMF) northward (Bn) and southward (Bs) turnings, and reverse shocks. The PPs are possibly the loop and filament portions of coronal mass ejections (CMEs). From a study of > 30 A GIC events, it is found that supersubstorm (SSS: SML < -2500 nT) and intense substorm (-2500 nT < SML < -2000 nT) auroral electrojet intensifications are the most frequent (76%) cause of all of these GIC events. These events occur most often (76%) in superstorm (SYM-H ≤ -250 nT) main phases, but they can occur in other storm phases and lesser intensity storms as well. After substorms, PPs were the most frequent causes of Mäntsälä GIC > 30 A events. Forward shocks were the third most frequent cause of the > 30 A events. Shock-related GICs were observed to occur at all local times. The two “Halloween” superstorms of 29-30 and 30-31 October 2003 produced by far the greatest number of GICs in the interval of study (9 > 30 A GICs and 168 > 10 A GICs). In the first Halloween superstorm, a shock-triggered SSS (SML < -3548 nT) caused 33, 57, 51 and 52 A GICs. The 57 A GIC was the most intense event of the superstorm and of this study. Equally intense magnetic storms were also studied but their related GICs were far less numerous and less intense.