Numerical Computations of Terrestrial ELF Electromagnetic Wave Fields in the Frequency Domain

The zero‐order term of the residue series has been employed to calculate the variation of field strength with distance over the earth's surface in the frequency band 7.8 Hz to 1 kHz. Spherical symmetry is assumed for the earth and ionosphere. The ionosphere is taken to be isotropic, but radial inhomogeneity is allowed. A vertical electric dipole source and a realistic propagation‐constant model were assumed. The computations indicate the accuracy of the usual approximations to the residue series and enable the magnitude of the standing wave effects in the earth‐ionosphere cavity to be assessed.