A Novel Method to Identify the Physical Mechanism and Source Region of ELF/VLF Waves Generated by Beat-Wave Modulation Using Preheating Technique

Abstract

One of the most important effects of ionospheric heating by HF (high-frequency) waves is the generation of ELF/VLF (extremely low-frequency/very low-frequency) waves by modulated heating. An important limitation of amplitude modulation (AM) is its dependence on ionospheric electrojet, which means to achieve better modulation effect, some strict spatio-temporal conditions must be met. To solve this problem, some possible methods have been proposed including beat-wave (BW) modulation. However, due to the controversy of its mechanism and the source region of the stimulated ELF/VLF waves, it is not clear whether it is an electrojet-independent method or not, which has become one of the hot topics in recent years. In this paper, we found that the effect of preheating on modulation efficiency of BW based on different theories is the opposite. We suppose the opposite character of the influence and effect on the efficiency of BW in D region and F region as a base for a novel method to identify the physical mechanism and source region of BW. This method can be feasible to solve the controversy of BW. The feasibility of this method is verified by simulation results in the paper.

Determine the Physical Mechanism and Source Region of Beat Wave Modulation by Changing the Frequency of HF Waves

“…In this section, simulations of magnetic field amplitudes of 1) BW in the D-E region, 2) BW in the F region and 3) superposition of BW in both D-E and F region received on the ground directly below the modulated heating source regions are presented (Physical models in Section 2 have been validated in Ref. [34]). Parameters of background ionosphere and atmosphere are chosen for 19 April 2015, 0600 UT, which were obtained by IRI-2016 and NRLMSISE-00 and the location of the HF transmitter is chosen as HAARP Facility (62.4°N, 145°W).…”