Book Description

The goal of this project is accurate prediction of high-altitude fields generated by low-altitude VLF sources to understand their influence on radiation belt dynamics. We applied a full-wave finite difference numerical model of the electromagnetic fields to compute the VLF energy injected through an arbitrary and, therefore, realistic ionosphere for a source located anywhere on the globe. A complete end-to-end run of the high-altitude VLF power prediction model has been completed using our modeled 130-km altitude VLF power predictions as the input to the higher altitude ray-tracing code. This resulted in good agreement with high-altitude VLF field measurements from the IMAGE satellite. A series of simulations using parameters corresponding to the NML (high latitude) and NPM (low latitude) transmitters showed that, for a given uniform grid spacing, the low-altitude fields can be computed correctly while the high-altitude fields are incorrect. This shows that a nonuniform grid approach, in which low altitudes are resolved coarsely and only the highest altitudes are resolved finely, is the key to achieving efficient simulations of high-altitude fields. Comparisons with results from the time domain code show that our preliminary frequency domain code gives answers in quantitative agreement with the time domain code but is about 90 times faster for single-frequency computations.