Model simulation of the large-scale high-latitude F-layer modification by powerful HF waves with different modulation

The mathematical model of the high-latitude ionosphere, developed earlier, is applied to investigate how the modulation regime of the ionospheric HF heating facility near Tromso, Scandinavia, affects the large-scale high-latitude F-layer modification. Simulations are made for distinct cases, in which high-power waves have different modulations, namely, for continuous wave transmission and for pulse operation, with the amplitude of the HF wave being square wave-modulated. The calculations are performed for different lengths of pulses and various time intervals between successive pulses. The frequency of HF waves is chosen to be close to the most effective frequency for the large-scale F2-layer modification. Simulations are made for autumn and low geomagnetic activity conditions both for nocturnal and for daytime conditions. The results of modeling indicate that the most considerable decrease in the F-region electron concentration may be achieved when the heater is operated continuously. Moreover, the perceptible decrease in the F-region electron concentration may take place when the heating facility is operated pulsatily. For the pulse operation, the amplitude of the electron concentration variations depends on the ratio of the length of pulses to the time interval between successive pulses. The higher the latter ratio is, the more the electron concentration variation amplitude ought to be.