A review of methods for coping with ionospheric variability in connection with HF systems

Ionospheric variability is one of the more fundamental problems encountered in the analysis of HF system performance, whether it be in the realm of hindcasting, nowcasting, or forecasting. In most instances the problem must be handled statistically. In some instances, typically in the arena of near-term forecasting, more deterministic approaches have been used. In general the approaches for coping with variability can be grouped into three basic categories: modeling, adaptive, and robust. Each category has its advantages and disadvantages, its advocates and adversaries. The author identifies methods in the indicated categories, and discusses attempts to improve ionospheric models