Simultaneous solutions of the differential equations governing electron energy and power flow are used to study D region absorption effects arising from high‐power HF heating. It is shown that self‐absorption of the heating wave can severely limit HF heating of the upper ionosphere and that the power density available for heating above the D region saturates as the heating power is increased. Models of the electron temperature distribution under heated conditions are used to compute the change in two‐way integral absorption on a 2.4‐MHz diagnostic wave due to HF heating as a function of heating frequency. The predicted theoretical absorption change is found to agree with experimental results.
A unique wave interaction experiment employing the Arecibo 2.0‐MW, 430‐MHz radar as disturbing or heating transmitter has been performed. The purpose of this experiment was to evaluate UHF electron heating effects and to extend the wave interaction technique to higher than usual heights (˜100 km). The heater beam used was much smaller in angular extent than the probing or wanted beam, yielding an unfavorable geometric weighting factor and making the experiment very sensitive to reflection properties of the E region. Nonetheless, wave interaction was easily detected using a completely digital signal processing technique. Comparison of experimental wave interaction results with a numerical model of the process indicates that lower thermosphere electron cooling rates are possibly too small by a factor of 4. Power spectra of the 3.155 MHz wanted signal (reflected from E region) amplitude fluctuations for ‘quiet’ and ‘disturbed’ days are also given.
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