Sensitivity of geomagnetically induced currents to varying auroral electrojet and conductivity models

Abstract

Geomagnetically induced currents (GIC) are created by the interaction of rapid changes in the magnitude of the magnetic field with the conductive subsurface of the Earth. The changing magnetic field induces electric currents, which are particularly strong along boundaries between regions of contrasting conductivity structure such as the land and sea. A technique known as the 'thin-sheet approximation' can be used to determine the electric field at the Earth's surface, which in turn allows the calculation of GIC in the earthing connections of high-voltage nodes within a power grid. The thin-sheet approximation uses a spatially varying conductance over the region of interest on a 2D surface, combined with a 1D layered model of upper lithosphere conductance. We produce synthetic models of the auroral electrojet in different locations over the United Kingdom (UK) and investigate the effects of varying the 2D thin-sheet model. We assess different two-dimensional surface conductance models and vary the underlying 1D conductivity models to simulate the effects of resistant through to conductive lithosphere. With an advanced network model of high-voltage electrical distribution grid, we compute the expected GIC at each node in the system given the input surface electric fields from the various synthetic electrojets and conductivity models. We find that the electrojet location is the primary control on the size of GIC, with conductivity being a second-order effect in general, though it can be locally important.

Influence of spatial variations of the geoelectric field on geomagnetically induced currents

“…The latter leads to spatial variations of the electric field even if the magnetic field is a uniform plane wave (Bedrosian & Love, 2015). In case of nonuniform magnetic fields, lateral variations of the ground conductivity can locally play a further significant role (Beggan, 2015).…”

“…However, simulations are still far from the capability to model precisely small-scale features and local enhancements that are important for GIC (cf. Pulkkinen et al, 2006;2015). By small scales we refer to variations of the geoelectric field in the scale of 10-100 km, which corresponds to typical lengths of power transmission lines in the region studied here.…”

“…Spatial variations are caused by a nonuniform geomagnetic field and by a laterally varying ground conductivity. The former is generally the major factor affecting GIC magnitudes (Beggan, 2015). The latter leads to spatial variations of the electric field even if the magnetic field is a uniform plane wave (Bedrosian & Love, 2015).…”

“…A common approach is to use long geomagnetic data sets to extrapolate indices (Siscoe, 1976;Love et al, 2015;Riley, 2012), or to extrapolate the amplitude of the variation field or its time derivative (Danskin & Lotz, 2015;Love et al, 2016;Thomson et al, 2011). A related possibility is to extrapolate the geoelectric field modelled from magnetic field data (Myllys et al, 2014;Nikitina et al, 2016;Pulkkinen et al, 2012;2015;Wintoft et al, 2016). In a few cases, there are long enough time series of the recorded electric field allowing for deriving statistics (Langlois et al, 1996).…”

Statistical analysis of extreme auroral electrojet indices

“…In the present study, we focus on auroral latitude geomagnetic activity caused by auroral electrojets. Because they cause intense GIC, the effect of auroral latitude geomagnetic activity on GIC has been intensively studied by many researchers (e.g., Beggan 2015). This auroral activity also causes polar-orbiting satellite anomalies due to the enhanced auroral electron precipitation.…”