Efficiency in ELF/VLF Generation by Pulsed HF-heating Gennady Milikh University of Maryland PARS-2 Workshop, November 3 – 6, 2002.

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Presentation transcript:

Efficiency in ELF/VLF Generation by Pulsed HF-heating Gennady Milikh University of Maryland PARS-2 Workshop, November 3 – 6, 2002

 The conversion of HF waves into ULF/ELF/VLF signals relies on the modulation of the electrojet current by amplitude modulated HF-heating  The spatio-temporal behavior of the modulated conductivity in response to HF-pulses determines the efficiency of ELF generation  The conversion efficiency strongly varies with the modulation frequency having peak at a few kHz

Objectives Present a theoretical model of ELF/VLF generation due to pulsed HF heating of the lower ionosphere Check the model against observations Make theoretical predictions of the waveforms due to coherent pulse sweeping. Find how such technique can improve the conversion efficiency.

Basic Theoretical Model Find the spatio-temporal profile of the current induced by the HF- heater (the first step) Compute the near field at the observation site by the retarded potential method (the second step)

Variations of Hall Conductivity caused by the HF-pulse and associated magnetic field on the ground

Experimental results along with theoretical predictions

The model allows us to study the waveforms synthesized by a set of HF-pulses  Coherent sweeping allows to increase the conversion efficiency since multiple pulses can be received in phase.  However, the sweeping can be conducted only within  30  angle which limits the number of HF-irradiated spots.

Effect of coherent sweeping. Synthesized waveforms as they could be observed beneath the HF-heated spots.

Effect of coherent sweeping. Synthesized waveforms as they could be observed beneath the HF-heated spots.

Effect of coherent sweeping. Synthesized waveforms, as they could be observed 150 km apart from the transmitter

Effect of coherent sweeping. Synthesized waveforms, as they could be observed 150 km apart from the transmitter.

Coherent sweeping with the pulses of gradually increasing amplitude, as they could be observed beneath the HF-heated spots

Summary The model of ELF/VLF generation is in a good agreement with the observations. According to the model the coherent sweeping can improve the generation efficiency in the range kHz. The efficiency improvement is moderate for the current ERP, while it will be significant for the full ERP.