Experimental study and modeling of HF radio wave propagation in the course of substorm event

The HF radio path Ottawa (Canada) - St. Petersburg (Russia) with the length of about 6600 km was considered. The main goals are to carry out numerical modeling of radio propagation for the path and to compare the model calculations with experimental results. The following basic results were obtained: The signal amplitude increases by 20¿30 dB 1¿1.5 hour before the substorm expansion phase onset. At the same time the signal azimuth deviates towards north of the great circle arc for the propagation path. Compared with quiet periods there are effects due to irregularities and gradients in the area of the polar edge of the main ionospheric trough on the passing signals. Propagation mechanisms also change during substorms. The growth of signal amplitude before the substorm could be used for forecasting of space weather disturbed conditions.