Wavelet cross-correlation dynamical network of the coherent GIC response to intense geomagnetic storms in the high voltage grid of Great Britain

During geomagnetic storms rapid magnetic variations cause large, sharp enhancements of the magnetic and geoelectric field at mid-latitudes. These present a potential hazard to grounded technology such as high voltage transformers, pipelines and railway systems. Spatio-temporal quantification can provide insight into the magnitude and configuration of their potential hazard. We perform a wavelet decomposition on both European ground-based magnetometer measurements and modelled Geomagnetically Induced Currents (GICs) from the high voltage grid of Great Britain (GB).  A wavelet decomposition localizes the signal in the time-frequency domain, and we show that in both magnetometer observations, and modelled GIC response, the Haar wavelet extracts the signal power and waveform at the signal fastest rate-of-change.

We then use Haar wavelet cross-correlation of the GIC in the grounded nodes to build a time-varying network of GIC coherent response around the GB grid during intense geomagnetic storms [1]  including the 2003 Halloween storm. We find a highly intermittent (few 10s of minutes duration) long-range coherent response that can span the entire physical grid at most intense times. The spatial pattern of coherent response seen in the GIC flow network does not simply follow that of the amplitude of the rate of change of B field that is estimated via the Haar wavelet. Coherent response is excited across spatially extended clusters comprised of a subset of nodes that are highly connected to each other, with a tendency for east-west linkages following that of the physical grid, simultaneous with  the overhead presence of the auroral electrojet and the inducing component of the magnetic field. This can quantify the spatial and temporal location of increased hazard in specific regions during large storms by including effects of both the geophysical and engineering configuration of the high voltage grid.

[1] L. Orr, S. C. Chapman, C. Beggan, Wavelet and network analysis of magnetic field variation and geomagnetically induced currents during large storms, Space Weather (2021) doi: 10.1029/2021SW002772