HF beam parameters in ELF/VLF wave generation via modulated heating of the ionosphere

Abstract

[1] ELF/VLF (0.3-30 kHz) wave generation is achievable via modulated HF (3-30 MHz) heating of the lower ionosphere in the presence of natural currents such as the auroral electrojet. Using the 3.6 MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, AK, we investigate the effect of HF frequency and beam size on the generated ELF/VLF amplitudes, as a function of modulation frequency, and find that generation in the Earth-ionosphere waveguide generally decreases with increasing HF frequency between 2.75-9.50 MHz. HAARP is also capable of spreading the HF power over a wider area, and we find that a larger beam area yields larger generated amplitudes on the ground. Measurements are shown to generally agree with a theoretical model, which is then applied to also predict the effect of HF beam parameters on magnetospheric injection with HAARP.

Multistation observations of the azimuth, polarization, and frequency dependence of ELF/VLF waves generated by electrojet modulation

“…Focusing on Figure a, it can be seen that the highest amplitude is observed at a modulation frequency of 2.125 kHz for all three sites in line with that observed in previous work [ Stubbe et al , ; Papadopoulos et al , ; Cohen et al , ]. However, after the first peak observed at 2.125 kHz at all sites, the next highest peaks observed at Chistochina and Paxson are at 4.3 kHz and 6.325 kHz.…”

“…At the Arecibo Observatory in Puerto Rico and at the Jicamarca Observatory in Peru HF facilities were used to generate weak ELF signals with the equatorial electrojets [ Ferraro et al , ; Lunnen et al , ]. The European Incoherent Scatter facility located in Tromsø, Norway, the High Frequency Active Auroral Research Program (HAARP), and the Sura ionospheric heating facility in Russia have been extensively utilized for the modulation of auroral electrojets [ Stubbe et al , ; Barr and Stubbe , ; Moore et al , ; Fujimaru and Moore , ; Cohen et al , ; Gołkowski et al , ; Cohen and Golkowski , ; Kotik et al , ]. The two main modes of heating the ionosphere are called the ordinary mode ( O mode) and the extraordinary mode ( X mode).…”

Modulation of auroral electrojet currents using dual modulated HF beams with ELF phase offset, a potential D‐region ionospheric diagnostic

“…Thus, the physical processes on all relevant timescales, including those identified by ] are taken into account. We note that this comprehensive model has been shown to closely match observations of HAARP‐generated ELF waves including copious measurements at the CH site []. For given HAARP beam parameters, a D‐region ionospheric profile and a receiver location, the comprehensive model is able to predict the phase and amplitude of ELF waves generated in the entire three‐dimensional heated region of the ionosphere.…”

100 days of ELF/VLF generation via HF heating with HAARP

“…On both days, a peak in the frequency response can be seen, starting at ∼2.3 kHz and descending down to ∼1.9 kHz toward the end of the recording. These result from cavity resonance between the Earth and the ionosphere [ Stubbe et al , ; Cohen et al , ], which are particularly strong close to the transmitter and will be discussed more later. The resonance frequency drops as the Sun sets over the ionosphere which greatly decreases the ionization, leading to a rise in the ionospheric reflection height and absorption altitude range.…”

“…We use here a three‐dimensional theoretical model to try to roughly estimate the radiated power using short‐range observations of the magnetic field. We apply a theoretical model of the HF to ELF/VLF conversion process that has been used and validated several times in connection with HAARP‐generated ELF/VLF signals [ Cohen et al , , , , ], so we describe it only briefly here. The model takes as input an ionospheric background condition and a realistic HF radiation pattern from HAARP.…”