Fig. 3(g). Relative permittivity ϵ/ϵ0 for left-hand circular (LHC, red) and right-hand circular (RHC,
blue) polarizations in the lower ionosphere (n=1010m−3, B=10 μT) as a function of frequency
from 1 kHz to 5 MHz. The cyclotron frequency fB≈280 kHz is marked by the resonance in the
RHC curve. Regions with ϵ/ϵ0>0 correspond to propagating waves, while ϵ/ϵ0<0 indicates
evanescent (reflected) waves. The RHC wave propagates below fB and above its cutoff near 1.05
MHz, but is evanescent between these frequencies. The LHC wave propagates only above its
cutoff near 0.77 MHz.