We have evaluated the ionization rate for protons in the altitude range relevant to VLF propagation, and for galactic cosmic ray (GCR) background, finding that at energies up to 鈭? GeV the ionization rate of solar protons exceeded the GCR ionization by 1.5 orders of magnitude.
We have applied the Long Wave Propagation Capability (LWPC) code to evaluate the enhancement of the electron density from VLF signal perturbation and have inferred corresponding electron densities from the evaluated ionization rates and effective recombination coefficients from literature, to find the two independent sets in good agreement.