Wave interaction observations of ionospheric modification in the D-region

Radio wave interaction measurements using the high power transmitter at Platteville resulted in cross modulation of up to 30 percent as compared to the earlier cross modulation measurements of 7 percent or less at low power. A theory is derived which shows that for a high power heating transmitter, the cross modulation is proportional to the square of the electron temperature. Additional measurements and theory are given which indicate that large radiated powers will produce fairly large electron density increases in the D-region, depending upon heating transmitter frequency and wave polarization. The heating of the ionospheric D-region apparently produces changes in the reflection process at low frequencies. Experimental data taken during solar flares, which support this conclusion, are presented.