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

Research output: Contribution to journalJournal article

Published

  • Mike J. Kosch
  • T. Pedersen
  • E. Mishin
  • M. Starks
  • E. Gerken-Kendall
  • D. Sentman
  • S. Oyama
  • B. Watkins
Journal publication date08/2007
JournalJournal of Geophysical Research
Volume112
PagesA08304
Original languageEnglish

Abstract

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.

Bibliographic note

Copyright (2007) American Geophysical Union. Further reproduction or electronic distribution is not permitted