Climatology of Maximum Usable Frequency at High Latitudes

High Frequency (HF) radio wave propagation at high latitudes is particularly difficult to predict due to the temporal and spatial complexity of the high-latitude ionosphere. Localized, large-magnitude variations in ionospheric electron density connected to geomagnetic activity can cause the maximum usable frequency to change dramatically, directly impacting technologies dependent on HF radio propagation such as long-distance communications, or over-the-horizon radar. In this study, the climatology of maximum usable frequency experienced for two high latitude HF radio links is analyzed across multiple years. One link spans the auroral oval, and the other is contained entirely in the polar cap. Apart from the diurnal variation in maximum usable frequency expected based on solar zenith angle, two significant features are identified. First, periods with strong geomagnetic activity, characterized using the Disturbance Storm Time (Dst) index, are correlated with decreases in maximum usable frequency for both links. These decreases are products of negative storm-time effects at high latitudes. Second, the link entirely contained in the polar cap exhibits increased maximum usable frequency beyond what is expected from diurnal variation at certain times of day and year. These times are consistent with the expected occurrence for polar cap patches, as predicted by well-known patch-formation models.