Proximity Effect on the Induced Geoelectric Field at the Lateral Interface of Different Conductivity Structures During Geomagnetic Storms

Abstract

The induced geoelectric fields and telluric currents generated during geomagnetic storms will be distorted by lateral variations of the Earth conductivity. The Galerkin finite element method (FEM) is a useful tool to analyze complicated electromagnetic field problems. In this paper, a uniform thin sheet current with infinite width located at 100 km above the Earth's surface is assumed to represent the source of geomagnetic variations. It is harmonic with the amplitude of 1 A/m at different frequencies. Three Earth conductivity structures are modelled where the basic model is horizontally uniform for comparisons. The second and third structures have the same exact thicknesses and conductivity values with the basic one on one side and five times greater or lower values on the other side to represent conductivity variation from low to high and from high to low. The computational results show that the abrupt changes of conductivities have influences on the induced telluric currents, which can be classified as the proximity effect and the skin effect. For GIC research in power systems, especially in systems located at coastal areas, the geoelectric field and GIC should be determined taking the directions of the transmission lines and of the coast into consideration. Both the proximity effect and the skin effect should be considered along with the coast effect in research of GIC impacts during geomagnetic disturbances. Boundary conditions discussed in this paper can be varied depending on different modelling techniques and on the scales of conductivity structure models.

The Role of Tectonic Plate Thickness and Mantle Conductance in Determining Regional Vulnerability to Extreme Space Weather Events: Possible Enhancement of Magnetic Source Fields by Secondary Induction in the Asthenosphere

“…We employ a generic Earth model with two subsurface parameters that affect MT impedances through their effects on electromagnetic fields-lithosphere thickness and asthenosphere conductance-to explain how regional differences to space weather vulnerability occur. We note that tectonic boundaries also affect induced electric fields that drive GICs in technological conductors (e.g., Dong et al, 2015). Therefore, we do not advocate using this model for estimating electric fields but only for elucidating the processes involved.…”

Proximity Effects of Lateral Conductivity Variations on Geomagnetically Induced Electric Fields

“…The scalar potential satisfies ∇ϕ = ∂ϕ ∂y e y = 0. The governing equations can be written as − 1 µ ∇ 2 A y + jωγ A y = J sy (12) and − 1 µ…”

“…The effects of lateral variation of the Earth conductivity structures on geoelectric fields depend on the E-and H-polarization and on the orientation of the electric field vector relative to the direction of the discontinuity [7]. The variation of the intensity of the E-field with distance from a discontinuity in conductivity can also be called a proximity effect [12]. The term ''proximity effect'' commonly refers to electromagnetic compatibility between nontouching conductors; however, the proximity effect in geoelectric fields involves the interaction between touching conductors on the Earth.…”

EMP/GMD Phase 0 Report, A Review of EMP Hazard Environments and Impacts

“…Finally, we note that it is also important to recognize that the induction of geo-electric fields is not entirely local. As mentioned above, the depth-resolved structure of the conductivity is very important; however, transverse variation in structure can also contribute to localized GMD enhancements, changing GMD amplitudes by an estimated 20% in some cases (Bo, Ze-Zhong, Lian-Guang, Li-Ping, & Chun-Ming, 2015). This enhancement can be interpreted as a generalization of the well-known geomagnetic "coast effect" (Parkinson & Jones, 1979), but is not well-understood in the context of storm-associated GMD threats.…”