Sensitivity of FDTD modeling of VLF Signals to D-Region Chemistry: Quiescent & Disturbed Conditions

Radio signals are strongly impacted by natural and artificial ionospheric disturbances which can be challenging to model. This is especially true of D- Region chemistry which is affected from below by shocks, acoustic-gravity waves and thunderstorm electric fields, and from above by solar x-rays, high-energy protons, and precipitating electrons. Detailed chemistry schemes have been developed by various research groups, with many 10s of species and many 100s of reactions, that have been used to calculate RF absorption during geomagnetic events. In contrast, advanced studies of VLF signal propagation typically employ reduced D-Region chemistry schemes [1]–[2], e.g., the four species Glukhov-Pasko-Inan scheme [3], that rely upon simplified parameterizations of electron attachment, detachment and recombination.