Statistics of auroral radio absorption in relation to prediction models

The prediction of HF propagation conditions at high latitude requires a knowledge of the statistics of radio absorption in the auroral ionosphere, a highly variable phenomenon depending on local time, magnetic latitude, season and solar activity. Data from riometer stations may be compiled to provide statistics on the auroral radio absorption. Questions regarding the probability distribution and variations with latitude, solar and geomagnetic activity, and longitude are considered. Difficulties concerning the smallest absorption values are pointed out.