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AGU: Geophysical Research Letters

 

Keywords

  • VLF whistler waves
  • HF heater-modulated electrojet
  • whistler mode current

Index Terms

  • Space Plasma Physics: Active perturbation experiments
  • Space Plasma Physics: Nonlinear phenomena
  • Space Plasma Physics: Wave/wave interactions
  • Space Plasma Physics: Wave/particle interactions
  • Space Plasma Physics: Turbulence

Abstract

GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L13101, 5 PP., 2008
doi:10.1029/2008GL034414

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

Spencer P. Kuo

Department of Electrical and Computer Engineering, Polytechnic University, Brooklyn, New York, USA

Yen-Liang Wu

Department of Electrical and Computer Engineering, Polytechnic University, Brooklyn, New York, USA

R. Pradipta

Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

J. A. Cohen

Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

M. C. Lee

Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA

Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts, USA

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.

Received 21 April 2008; accepted 2 June 2008; published 1 July 2008.

Citation: Kuo, S. P., Y.-L. Wu, R. Pradipta, J. A. Cohen, and M. C. Lee (2008), VLF wave generation by amplitude-modulated HF heater waves at Gakona, Alaska, Geophys. Res. Lett., 35, L13101, doi:10.1029/2008GL034414.

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