Interpolation of external magnetic fields over large sparse arrays using Spherical Elementary Current Systems

Estimation of external magnetic field disturbances to a point remote from an observatory can be made, for example, by using the latitudinal-weighted arithmetic mean of the field measured at two other observatories, one to the north and one to the south of the point of interest. An alternative technique for interpolating external magnetic field disturbances across large spatial areas can be achieved with the Spherical Elementary Current System (SECS) method using data from a number of ground-based magnetic observatories. The SECS method represents the complex electrical current in the ionosphere as a simple set of equivalent currents placed at a specific altitude. The magnetic field recorded at observatories can be used to invert for the electrical currents and subsequently used to interpolate or extrapolate the magnetic field across a large area.