Wavelet and Network Analysis of Magnetic Field Variation and Geomagnetically Induced Currents During Large Storms. Issue 9 (9th September 2021)

• Record Type: Journal Article
• Authors: Orr, L.; Chapman, S. C.; Beggan, C. D.
• Is Part Of: Space weather. Volume 19:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-09
• Subjects: space weather -- ground induced currents -- networks -- wavelets; Space environment -- Periodicals; 551.509992
• DOI: 10.1029/2021SW002772
• Languages: English
• ISSNs: 1542-7390

Abstract

Abstract: 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. Spatiotemporal quantification can provide insight into the magnitude and configuration of their potential hazard. We use the Haar wavelet transform to localize in time and frequency the storm‐time response in both European ground‐based magnetometer measurements and modeled geomagnetically induced currents (GICs) from the high voltage grid of Great Britain (GB). Wavelet cross‐correlation of the GIC in the grounded nodes is then used to build a time‐varying network of GIC flow around the GB grid during storms including the 2003 Halloween storm. We find a highly intermittent (few tens of minutes duration) long‐range coherent response that can span the entire physical grid at most intense times. The spatial pattern of response seen in the GIC flow network does not simply follow that of the amplitude of the rate of change of B field. 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. Plain Language Summary: The rate of change of the magnetic field during large geomagnetic storms is a key parameter that drives the creation of geoelectric fields in the Earth's subsurface. These geoelectric fields can damage and degrade grounded technology such as high voltage transformers, pipelines and railway systems. By combining maps of the geoelectric field with a representation of the physical power grid we can compute if damaging Earth currents flow in individual high voltage transformers, in our case for Great Britain. Using magnetic data measured from 50 ground‐based stations in Europe, we apply a wavelet technique to understand where the greatest rate of change of the magnetic field, or step change, occurs and how energy is distributed in time and space. Next, we apply the wavelet technique in combination with correlation analysis to currents computed for large geomagnetic storms. The correlation analysis allows us to observe "networks" of transformers whose currents co‐vary together. We find that the connection behavior of the transformers are not as expected, forming discrete "islands" or clusters of small networks. Their locations are strongly linked to the extent of the overhead auroral currents. Key Points: Wavelet analysis of spatial and temporal magnetic variation during large geomagnetic storms Network correlation analysis of coherently induced currents form long‐range connections across the high voltage grid Network connections indicate a time‐localized coherent response to the electrojet and are a proxy for geomagnetically induced currents