Nighttime ionospheric D region: Equatorial and nonequatorial

摘要

Nighttime ionospheric D region parameters are found to be generally well modeled bythe traditional H' and as used by Wait and by the U.S. Navy in their Earth-ionosphereVLF radio waveguide programs. New comparisons with nonequatorial, mainly all-seaVLF path observations reported over several decades are shown to be consistent withthe previously determined height H' — 85.0 km and sharpness ,3 ti 0.63 km-1. Thesepaths include NPM (Hawaii) to Washington, D. C., Omega Hawaii and NLK (Seattle) toJapan, NWC (N.W. Australia) to Madagascar, and NBA (Panama) to Colorado. In markedcontrast, transequatorial path observations (even when nearly all-sea) are found to beoften not well modeled: for example, for Omega Japan and JJI (Japan) to Dunedin, NewZealand, the observed amplitudes are markedly lower than those which would be expectedfrom H' — 85.0 km and 13 0.63 km-1, or any other realistic values of H' andOther transequatorial observations compared with modeling include NWC to Japan,Omega Hawaii to Dunedin, and NPM (Hawaii) to Dunedin. It is suggested that the effectsof irregularities in the equatorial electrojet may extend down into the nighttime D regionand so account for the observed equatorial VLF perturbations through scattering ormode conversion.