A parameterized model of X-ray solar flare effects on the lower ionosphere and HF propagation

We present a parameterized X-ray solar flare effects model relating the physics of radiation transport to the observable impact of solar flares on low-altitude ionospheric absorption of High Frequency (HF) signals. Tunable parameters of time-varying flare spectral energy density and characteristic flare temperature provide a novel capability to simulate HF experiments over a wide range of X-ray solar flare behavior. Results from our model are consistent with HF propagation data collected over a period of heightened solar flare activity during 5–7 September 2017, including M and X class solar flares. Our predictions and measurements are compared with results from D Region Absorption Prediction (Akmaev et al., 2010, https://www.ngdc.noaa.gov/stp/drap/DRAP-V-Report1.pdf) and the Wait Very Low Frequency (VLF)-driven model (Wait & Spies, 1964).