Geomagnetically Induced Currents in High Voltage Transmission Lines: Solar Modal Signatures and Transfer Functions

English Abstract:

The sun has thousands of normal modes. In the power spectrum, these modes are expected to manifest as many thousands of line components whose energies can persist for upwards of thousands of years, in the case of solar gravity modes. Modal signatures have been detected in the interplanetary magnetic field (IMF) (Thomson et al., Nature 376, 1995), and in many man-made systems at Earth such as cellular telephones and ocean cables (Thomson et al., Proc. IEEE 95:5, 2007). Thomson et al (2007) also demonstrated evidence for coupling between the IMF and Earth's geomagnetic field.

In this paper we investigate: (1) whether solar normal modes are present in the form of geomagnetically induced currents (GICs) on high voltage electrical transmission lines, and (2) the relationship between the IMF, the local geomagnetic field, and GICs. In many ways, our work parallels efforts in magnetotellurics, albeit over a reduced frequency range. We find strong evidence for solar normal modes in GICs. However, the estimated transfer functions between the local geomagnetic field and GICs exhibit a large amount of variability as a function of frequency rather than being slowly varying as in the case of magnetotellurics.