Two charts showing simulated geoelectric fields along a profile running south-east to north-west through New York City
Simulated geoelectric fields along a profile running south-east to north-west through New York City (city location marked by the vertical black line, and that of the coast by the adjacent dashed vertical line). The simulation is driven by geomagnetic variations observed during the 2015 St Patrick’s Day storm, at the times shown in the top of the figures. The red and blue lines indicate geoelectric fields, perpendicular to the coast, derived using two different conductivity models that both include the effect of highly-conducting sea water, and hence show enhanced fields at the coast. They also show a step change in these fields at the transition from shallow to deep sea (marked by the vertical dashed line to the right of each panel, thus A indicates land, B shallow sea, and C deep sea).The green lines indicate simulated geoelectric fields modelled without sea water. Credit: Marshalko et al. [2020], Figure 10, top panels
Source: Space Weather

The conductivity of the solid Earth, and of its seas, plays a critical role in mediating the risk that space weather poses to electrically grounded infrastructures, most obviously the transmission grids that enable electrical power to be transported over long distances. These grids are vital for modern energy systems as we exploit power sources (e.g. wind, solar, hydro, nuclear) that are often distant from population centers.

However, over the past 80 years, we have learned that grid operations can be disrupted when geomagnetic storms induce significant electric fields at the surface of the Earth. The size of those fields is strongly dependent on ground conductivity and on proximity to highly conducting sea water.

Marshalko et al. [2020] use a range of conductivity models to estimate the geoelectric fields induced in the eastern United States by a moderate magnetic storm. These models include both realistic and simplified models of the 3D conductivity structures within the Earth, as well as changes in sea conductivity arising from variations in sea depth.

The results confirm that there are strong enhancements of the geoelectric field close to coasts, and also arising from inhomogeneities in ground conductivity. These enhancements contribute significantly to the voltages that arise from integration of geoelectric fields (as along grid lines), showing the importance of 3D conductivity when assessing space weather risks to transmission grids.

The results highlight that the enhancement of geoelectric fields has a component parallel to the coast, as well as perpendicular to the coast. Thus, it has potential to impact grounded infrastructures (e.g. grid lines, pipelines, rail systems) where these run parallel to coasts (a common occurrence due to land topography and focusing of population centers near coasts).

Citation: Marshalko, E., Kruglyakov, M., Kuvshinov, A., Murphy, B. S., Rastätter, L., Ngwira, C., & Pulkkinen, A. [2020]. Exploring the influence of lateral conductivity contrasts on the storm time behavior of the ground electric field in the eastern United States. Space Weather, 18, e2019SW002216.

—Michael A. Hapgood, Editor, Space Weather

Text © 2020. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.