Modeling of HF propagation at high latitudes on the basis of IRI

The relative error of calculation of MUF values averaged for all the cases for one hop was 23.6% by the initial IRI model. This error was decreased by 4% for the calculations on the basis of observed ТЕС and by 6% for the adaptation to foF2. The higher the latitude of the studied radio path, the more the difference between the observed and simulated MUF values. The conclusion was made that a principal cause of this difference was the deviation of calculated maximum ionospheric height values (hmF2) from the observed hmF2. The additional model update using hmF2 values obtained from Tromso station let to better match between the calculated MUF values and the observed MUF values for all radio paths. The analysis of experimental data showed that the non-predicted events (like traveling ionospheric disturbances, M- and N-modes, lateral modes, triplets, unusual scatter effects, etc.) sometimes took place at high latitude paths even during the quiet conditions.