Validation of the operational D-Region Absorption Prediction (D-RAP) model at the NOAA Space Weather Prediction Center

Airlines rely solely on high-frequency (HF) transmissions in the regions where satellite communications are not available, such as on cross-polar routes. Long-range HF communications are possible due to the reflection of radio waves from the peak of the ionospheric F2 layer at about 300 km altitude, but along the path to the F2 peak and back the radio wave signal suffers attenuation due to absorption by the intervening ionosphere. Most of the absorption occurs in the ionospheric D region (50–90 km altitude) where the product of the electron density and the electron-neutral collision frequency attains a maximum. Significant changes of the absorption strength occur as a result of sudden increases of electron density during solar X-ray flares on the dayside or solar energetic particle (SEP) precipitation in the polar regions. A new D-Region Absorption Prediction (D-RAP) model has recently been transitioned to operations at the NOAA Space Weather Prediction Center. A comprehensive validation effort has been undertaken using data from 6 mid- and high-latitude Northern Hemisphere riometer stations during 13 solar X-ray and SEP precipitation events during the last solar cycle. Performance of the model at particular sites will be illustrated and event specific and cumulative statistics presented. Plans for further model improvements and continuous validation will also be outlined.