VLF wave generation by beating of two HF waves in the ionosphere

• Published in: Geophysical research letters 2011-05, Vol.38 (10), p.n/a
• Main Authors: Kuo, Spencer, Snyder, Arnold, Kossey, Paul, Chang, Chia-Lie, Labenski, John
• Format: Article
• Language: English
• Subjects: Atmospheric sciences; density irregularities; digisonde; Earth sciences; Earth, ocean, space; Exact sciences and technology; filamentation instability; Gravity; Heaters; Inertia; Ionosphere; Plasma physics; Space; VLF wave generation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL047514

Theory of a beat‐wave mechanism for very low frequency (VLF) wave generation in the ionosphere is presented. The VLF current is produced by beating two high power HF waves of slightly different frequencies through the nonlinearity and inhomogeneity of the ionospheric plasma. Theory also shows that the density irregularities can enhance the beat‐wave generation. An experiment was conducted by transmitting two high power HF waves of 3.2 MHz and 3.2 MHz + f, where f = 5, 8, 13, and 2.02 kHz, from the HAARP transmitter. In the experiment, the ionosphere was underdense to the O‐mode heater, i.e., the heater frequency f0 > foF2, and overdense or slightly underdense to the X‐mode heater, i.e., f0 < fxF2 or f0 ≥ fxF2. The radiation intensity increased with the VLF wave frequency, was much stronger with the X‐mode heaters, and was not sensitive to the electrojet. The strongest VLF radiation of 13 kHz was generated when the reflection layer of the X‐mode heater was just slightly below the foF2 layer and the spread of the O‐mode sounding echoes had the largest enhancement, suggesting an optimal setting for beat‐wave generation of VLF waves by the HF heaters. Key Points Beating of 2 HF heaters is viable for ionosphere electrojet‐indep VLF generation Radiation intensity increases with VLF freq. and is enhanced by irregularities Define an optimal setting for beat wave generation of VLF waves by HF heaters