Analysis of the characteristics of modulated heating radiation wave in the high latitude ionosphere

This paper presents the radiation characteristics of ULF/VLF electromagnetic wave excited by the ionospheric modulated heating in the high-latitude based on the experimental data of the ionospheric modulated heating conducted by Chinese scientific researchers using the European Incoherent Scatter (EISCAT) heating facility in 2017−2019. The effects of heating power, heating wave polarization, radiation frequency and geomagnetic disturbance on the electromagnetic wave intensity of ULF/VLF under two modulated heating modes of natural current modulation (AM) and dual-frequency double-beam modulation (BW) are experimentally analyzed. The results show that the intensity of the excitation radiation wave is approximately proportional to the heating power, and the power ratio coefficients of AM and BW are about 1.7 and 2.1, respectively. The heating wave employed with X wave is more beneficial to stimulate ULF/VLF electromagnetic wave radiation when compared to employing O wave. With the increase of the radiation wave frequency, the intensity of the radiation wave first increases and then decreases, but the maximum intensity of the radiation wave excited by AM and BW heating occur at 2 kHz and 8−14 kHz, respectively. The intensity of the radiation source excited by AM depends on the magnitude of the natural current in the ionosphere, while the intensity of the radiation wave excited by BW has little correlations with the intensity of the natural current. Finally, in perspective of the current hot issue of ionospheric modulation heating, the question of where is the location of the BW source in the ionosphere is raised. The differences in the propagation characteristics of ULF/VLF electromagnetic waves excited by two modulated heating modes are compared by combining the experimental and theoretical analysis methods. It is confirmed that the radiation source formed in the BW mode is likely to be located in the F region, which is different from the AM mode.