Effects of Ionospheric Conductivity and Ground Conductance on Geomagnetically Induced Currents During Geomagnetic Storms: Case Studies at Low‐Latitude and Equatorial Regions

Abstract

Geomagnetic field variations recorded by fluxgate magnetometers are used to evaluate geomagnetically induced currents (GICs) under the equatorial electrojet (EEJ) and South Atlantic Magnetic Anomaly (SAMA) during two geomagnetic storms in March and June 2015. Geomagnetic stations with information about the underground electrical conductivity structure and that can be approximated by unidimensional (1‐D) models for calculation of the geoelectric field are selected. GICs levels are estimated using a realistic local power grid model located in the central region of Brazil, artificially moved to the sites where the geomagnetic measurements are available. GIC magnitudes are not large during the storms, and a maximum amplitude of 3.8 A was estimated at an equatorial station positioned over high resistivity underground during the main phase of the June storm. Effects of the ionospheric currents over the measurement sites and of the conductivity distribution beneath these sites are also evaluated. It is observed that both (EEJ) and (SAMA) increase the GICs amplitudes, with the greatest effects associated with daytime (EEJ) currents. A cutoff frequency was identified for both the (EEJ) and (SAMA) so that signals with frequencies lower than 2 mHz (periods longer than 500 s) are not amplified by the ionospheric currents. In relation to the underlying conductivity structure, GIC magnitude is affected by variation of the surface impedance and the sampling rate of the geomagnetic field. In our case, differences in amplitude of the surface impedance at the Nyquist frequency control the relative effects of the ground conductance between the stations.

The Role of Global/Regional Earth Conductivity Models in Natural Geomagnetic Hazard Mitigation

“…As expected, the relative GIC magnitudes are controlled by the electrical conductivity profile (surface impedance) and the sampling rate of the geomagnetic field (1 sample per minute, in this case). Espinosa et al (2019) suggest that crustal variability, particularly that of the upper crust, is primarily responsible for the observed variations due to the Earth's impedance.…”

“…Finally, a recent analysis by Espinosa et al (2019) focused on the effects of both ionospheric and ground electrical conductivity on GICs at the geomagnetic equator in Brazil. To circumvent the relative lack of MT data in Brazil, four magnetometers from the Embrace MagNet network (Denardini et al 2018) were chosen at such locations that the underground geological structure was amenable to 1D interpretation.…”

“…In an approach similar to Viljanen et al (2013), a power grid model was set up based on a 500 kV network operated in central Brazil, with some of the network parameters adopted from de Silva Barbosa et al (2015), and the others set to default values that provided the best fit to measured GICs. By analogy, we assume that power-line integration of the electric fields was performed; however, the boundaries of the four conductivity models are not indicated in Espinosa et al (2019), and a detailed discussion of the procedure is absent. The single modeled-to-measured GIC comparison presented in the paper suggests that this methodology is on a par with other international results based on a similar approach and can sometimes reproduce up to 60-80% of the variations.…”

A Review of Geomagnetically Induced Current Effects on Electrical Power System: Principles and Theory

“…In contrast to this concept, GICs were detected in several power systems in mid-low latitude countries, for example, South Africa [87], Spain [88] and New Zealand [54]. However, the 2003 GMD event has received attention and especially motivated GIC analysis in mid-low latitude countries, and as a result, many studies have been conducted, for example, on Argentina [89], Czech Republic [90], New Zealand [91][92][93][94] , Brazil [95][96][97], South Africa [98,99], China [100][101][102], Japan [103,104] , Kenya [105], Australia [106][107][108] , continental analysis of Europe [56], Spain [88,109], Switzerland [110], Greece [111], Namibia [112], Uruguay [113], Austria [114], Ethiopia [115,116], South Korea [117], Italy [118], and Mexico [119]. In high-latitude countries, the induced geoelectric field in the east-west direction is remarkable.…”

Evaluation of the Solar Quiet Reference Field (SQRF) Model for Space Weather Applications in the South America Magnetic Anomaly

“…Also, several authors use magnetic field measurements to estimate the magnitude of disturbed and storm-time periods driven by solar events (e.g., Klausner et al, 2016;Bolzan et al, 2018;Denardini et al, 2018b). Other studies estimate the magnitude of Geomagnetic Induced Currents (GICs) from those ground-based observations (e.g., Espinosa et al, 2019;Rodger et al, 2020).…”