Comparative study of two assimilative models of the ionosphere

Two assimilative models of the ionosphere are described: the Electron Density Assimilative Model (EDAM), developed by QinetiQ, and the IonoNumerics model developed by Fusion Numerics, Inc. Output from each technique has been compared to independent validation data measured by oblique and vertical ionosondes. Results indicate that when tested against vertical ionosondes, both models can reduce RMS errors compared to a median model. For example, the daytime RMS errors in the F region critical frequency above the Eglin Air Force Base ionosonde are 1.2 MHz for the Parameterised Ionospheric Model, 0.7 MHz for EDAM, and 1.0 MHz for IonoNumerics. Testing conducted against an oblique ionosonde has helped to expose a potential problem with ionospheric h(m)F(2) due to poorly specified empirical driver models within IonoNumerics. The testing shows the usefulness of ray-tracing experiments for improving numerical models and the limitations of only testing models against independent total electron content measurements.