An Electron Density Model of the D- and E-Region Ionosphere for Transionospheric VLF Propagation

摘要

Terrestrial Very-Low-Frequency (VLF) energy from both lightning discharges and radio transmitters has a role in affecting the energetic electrons in the Van Allen radiation belts, but quantification of these effects is particularly difficult, largely due to the collisional damping experienced in the highly variable electron density in the D- and E-region ionosphere. The Faraday International Reference Ionosphere (FIRI) model was specifically developed by combining lower-ionosphere chemistry modeling with in situ rocket measurements, and represents to date the most reliable source of electron density profiles for the lower ionosphere. As a full-resolution empirical model, FIRI is not well suited to D- and E-region ionosphere inversion, and its applicability in transionospheric VLF simulation and in remote sensing of the lower ionosphere is limited. Motivated by how subionospheric VLF remote sensing has been aided by the Wait and Spies (WS) profile (Wait Spies, 1964), in this study, we parameterize the FIRI profiles and extend the WS profile to the E-region ionosphere by introducing two new parameters: the knee altitude h(k) and the sharpness parameter for the E-region ionosphere beta(E). Using this modified WS profile, we calculate the expected signals at different receiver locations from the NAA, NPM, and NWC transmitters under the full range of possible ionospheric conditions. We also describe and validate a method about how these results can be readily used to translate VLF measurements into estimates of the lower ionosphere electron density. Moreover, we use this method to evaluate the sensitivity of different ground receiver locations in lower-ionosphere remote sensing.