Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program

Details Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program

Aug 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007jgra..11208304k&link_type=abstract

Journal of Geophysical Research, Volume 112, Issue A8, CiteID A08304

Physics

11

Ionosphere: Active Experiments, Ionosphere: Auroral Ionosphere (2704), Ionosphere: Wave Propagation (0689, 3285, 4275, 4455, 6934), Electromagnetics: Plasmas

Scientific paper

On 4 February 2005 the High-Frequency Active Auroral Research Program (HAARP) facility was operated at 2.85 MHz to produce artificial optical emissions in the ionosphere while passing through the second electron gyroharmonic. All-sky optical recordings were performed with 15 s integration, alternating between 557.7 and 630 nm. We report the first optical observations showing the temporal evolution of large-scale pump wave self-focusing in the magnetic zenith, observed in the 557.7 nm images. These clearly show that the maximum intensity was not reached after 15 s of pumping, which is unexpected since the emission delay time is <1 s, and that the optical signature had intensified in a much smaller region within the beam after 45 s of pumping. In addition, adjacent regions within the beam lost intensity. Radar measurements indicate a plasma depletion of ~1% near the HF reflection altitude. Ray tracing of the pump wave through the plasma depletion region, which forms a concave reflecting radio wave mirror, reproduces the optical spatial morphology. A radio wave flux density gain of up to ~30 dB may occur. In addition, the ray trace is consistent with the observed artificial optical emissions for critical plasma frequencies down to ~0.5 MHz below the pump frequency.

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