TY - JOUR

T1 - Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program

AU - Kosch, Mike J.

AU - Pedersen, T.

AU - Mishin, E.

AU - Starks, M.

AU - Gerken-Kendall, E.

AU - Sentman, D.

AU - Oyama, S.

AU - Watkins, B.

N1 - Copyright (2007) American Geophysical Union. Further reproduction or electronic distribution is not permitted

PY - 2007/8

Y1 - 2007/8

N2 - 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.

AB - 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.

KW - heating DCS-publications-id

KW - art-860

KW - DCS-publications-credits

KW - iono-fa

KW - DCS-publications-personnel-id

KW - 7

U2 - 10.1029/2007JA012264

DO - 10.1029/2007JA012264

M3 - Journal article

VL - 112

SP - A08304

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

SN - 0148-0227

ER -