Theory of very low frequency/extra low frequency radiation by dual-beam beat wave heating ionosphere

Abstract

At high latitudes, the proposed dual-beam beat wave method has become the focus of research because of its relative amplitude modulation method. The very low frequency/extra low frequency(VLF/ELF) radiation intensity does not depend on the background of the current, and can be used as an importantparameter of VLF/ELF radiation in poor background conditions. As for the background of weak natural current in middle and low latitude regions, the amplitude modulation method stimulates the VLF/ELF radiation effect poorly, therefore, at the low latitudes, the relative amplitude modulation method, dual-beam beat waves method may be more effective. In this paper, according to the pondermotive nonlinear heating theory in the upper ionosphere, a simulation model is presented about VLF/ELF radiation generated by dual-beam heating of the ionosphere via beating waves. This model is validated by calculations and the available experimental parameters. Based on this model, a comprehensive analysis is performed, involving the dependences of radiation intensity on various parameters such as latitude, effective radiation power(ERP), heating frequency, polarization, experimental times, and beating frequency difference. Then, we compare the dual-beam beat wave method with the amplitude modulation in stimulating VLF/ELF signals in the low and moderate latitude regions. Several conclusions are drawn as follows. First, the increases of geomagnetic declination and ERP of the heating facility may lead to a considerable improvement in radiation efficiency. Second, the X-mode polarization is more efficient for radiation than the O-mode polarization. Third, the most remarkable radiation effect may appear at winter night. The optimal heating frequency and the beating wave difference could be found under certain conditions. Stimulations of VLF/ELF radiation with the dual-beam beating wave method are more effectivethan the available amplitude modulation, the difference in VLF/ELF radiation intensity between the two methods is about 10 dB.