Fig. A.1.From: Deriving the geomagnetically induced electric field at the Earth’s surface from the time derivative of the vertical magnetic fieldGeometry of calculating components of matrices T and S. The elementary system is located at (θel, ϕel) and the result is evaluated at (θ, ϕ). θ′ is the co-latitude of the point (θ, ϕ) in the coordinate system centered at the elementary system.Back to article page