Validation of an Empirical Model of HF Radio Absorption during Solar X-Ray Flares

Military operations depend on high frequency (HF) radio communication. During a solar x-ray flare, the D-region of the ionosphere absorbs the HF radio wave energy, attenuating the signal, causing critical communication lines to fail. This research evaluates the performance of two empirical models that measure solar flare-induced HF absorption: The D-region Absorption Prediction (DRAP) model provided by the Space Weather Prediction Center and the Empirical HIDIVE Absorption (EHA) model developed by Air Force Institute of Technologys Evelyn Schumer in her 2010 dissertation. The DRAP model scales frequency as f -1.5 while normalizing the data by a cos0.75() dependence. The EHA model is scaled as f -1.24and normalizes by a cos0.9() dependence. Our statistical regression model improves flare-induced HF absorption modeling capabilities. It is built to perform at the 30 MHz frequency for the midlatitude riometers and normalizes the data using cos1.0(). We found the EHA model has a bias to overpredict flare size while the DRAP model trends to underpredict absorption. Our model outperforms the DRAP and EHA models for predicting solar flare induced HF absorption with the lowest RMSE value at 0.267, while the EHA model performed second best with an RMSE of 0.862 and the DRAP had an RMSE at 1.007.