VLF wave generation by amplitude-modulated HF heater waves at Gakona, Alaska

• Published in: Geophysical research letters Vol. 35; no. 13; pp. L13101 - n/a
• Main Authors: Kuo, Spencer P., Wu, Yen-Liang, Pradipta, R., Cohen, J. A., Lee, M. C.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 01.07.2008; Blackwell Publishing Ltd
• Subjects: Active perturbation experiments; Earth sciences; Earth, ocean, space; Exact sciences and technology; HF heater-modulated electrojet; Nonlinear phenomena; Space Plasma Physics; Turbulence; VLF whistler waves; Wave/particle interactions; Wave/wave interactions; whistler mode current; United States; Alaska; USA, Alaska; whistler mode current; HF heater-modulated electrojet; VLF whistler waves; experimental studies; altitude; density; Very low frequency radiation; North America; Whistler wave; frequency; intensity; currents; amplitude; Dipole; warming; Wave generation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2008GL034414

Experiments conducted at Gakona, Alaska, using the intensity‐modulated HF heating waves to interact with electrojet currents for the generation of VLF waves, are reported. An unexpected large increasing rate from 4 to 8 kHz in the frequency dependency of the VLF radiation intensity was observed. The peak value at 8 kHz was intense (about 7.5 dB above that of the 2 kHz signal used as a marker) and the wave intensity from 5 to 17 kHz appeared to be abnormally high (i.e., stronger than that at 2 kHz). In the experiments, we also observed the enhancement of spread‐E irregularities at electrojet current altitudes due to the amplitude‐modulated heater wave. These results and theoretical analyses suggest that temporally modulated electrojet currents mix with heater wave‐excited density irregularities to form whistler mode currents, which generate VLF whistler waves directly with much larger intensities and better directivity than a Hertzian dipole can.