VLF modes below a composite anisotropic ionosphere

The TM and TE modes excited by horizontally and vertically polarized line sources are investigated for composite ionosphere models and for high- and low-ground conductivities. The daytime propagation characteristics are comparable to those of a simpler exponential model. In nighttime propagation, the TE2mode has a smaller perturbing effect than in simpler ionosphere models; the ratio of TE to TM field components may change for various directions of propagation in such a way that a quasi-TE (or TM) mode appears to change into a quasi-TM (or TE) mode.