Book excerpt: An extensive literature survey has identified a number of low-frequency noise measurements relevant to the effects of ionospheric disturbances on ELF propagation. These measurements pertain to the behavior of earth-ionosphere cavity resonances and ELF/VLF noise intensity at the time of: (1) the Starfish high-altitude nuclear detonation, (2) more than thirty solar flares, and (3) two polar-cap-absorption events (PCAs). Until controlled-source ELF experiments are carried out under disturbed conditions, these collateral data provide the only means by which codes that predict ELF propagation in nuclear environments can be compared with experiment. A full-wave propagation code similar to predictive codes developed under DNA auspices is used to compute ELF propagation anomalies due to Starfish, PCA events, and a large number of model x-ray flares. The results of these calculations are compared--to the extent possible--to the available data. Despite the inadequacies of the data, we are able to verify key theoretical predictions. Good agreement is demonstrated between code predictions and ELF/VLF noise intensity during solar flares. Both experiment and theory consistently show that the vast majority of flares cause the intensity to increase at frequencies between 30Hz and 1 kHz, decrease between 5 kHz and 10 kHz, and increase between 10 kHz and 30 kHz. This agreement, which occurs over three frequency decades, strongly implies the correctness of the predictive codes.