Predicting the Day-to-Day Variability of the Mid-Latitude Ionosphere for Application to HF Propagation Predictions

Abstract : Hourly values of ground-based ionosonde data have been subjected to a detailed statistical analysis in order to determine the day-to-day variability displayed by various ionospheric regions. It is found that the standard deviation about the observed F2 region monthly median critical frequency is two to three times that observed in the E and F1 regions at mid-latitudes. The day- to-day variability of foE and foF1 is such that monthly median values of those parameters can be used to represent the daily variation in the E and F1 region. This would imply that HF prediction programs which rely on median data for specification of the ionosphere yield results that can be used in day-to-day operations for those propagation modes that are controlled by the E and F1 region. As the F2 region is highly variable, a method of using timely observations of foF2 to predict the expected values of the F2 region critical frequency has been developed. The method has the advantage that errors in predicting the monthly median foF2 can be averted and the predicted values are generally closer to the actual observations than the observed monthly median.