Solar X-Ray Spectrum Definition and the Prediction of Ionospheric Radio Wave Propagation.

The effects of deviations in determination of solar X-ray spectra on predictions of hf and vlf radio wave propagation parameters were determined for various levels of solar activity. For analytical purposes, the form that the uncertainties in the X-ray measurements assumed was that of uncertainties in the temperature of the solar emitting region as opposed to uncertainties in emission measure. The temperatures used to represent the various levels of solar activity were 5, 10, 15, and 20 x 10 to the 6th power. The uncertainties in temperature T were represented by T plus or minus percent change X T where the percent changes were 0, plus or minus 10, plus or minus 25, and plus or minus 50. It is determined that for predictions of hf absorption, X-ray spectral definition is required to be better than plus or minus 25 for low temperatures and plus or minus 50 for high temperatures. Vlf prediction requires the spectra to be known to at least plus or minus 50 and probably plus or minus 25.