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Ann. Geophys., 26, 1089-1099, 2008
www.ann-geophys.net/26/1089/2008/
© European Geosciences Union 2008
Observations of artificial and natural optical emissions at the HAARP facility
T. Pedersen1, R. Esposito1, E. Kendall*,2, D. Sentman3, M. Kosch4, E. Mishin5, and R. Marshall6
*formerly: Gerken
1Space Vehicles Directorate, Air Force Research Laboratory, AFRL/VSBXI, 29 Randolph Rd., Hanscom AFB, MA 01731, USA
2SRI International, 333 Ravenswood Avenue, Menlo Park CA 94025, USA
3Geophysical Institute, University of Alaska, Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, USA
4Department of Communications Systems, Lancaster University, InfoLab21, Lancaster University, Lancaster LA1 4WA UK
5Institute for Scientific Research, Boston College, AFRL/VSBXI, 29 Randolph Rd., Hanscom AFB, MA 01731, USA
6STAR Lab, Stanford University, 350 Serra Mall, Stanford, CA 94305, USA
Abstract. Extensive optical observations have been carried out at
the High Frequency Active Auroral Research Program (HAARP) ionospheric
heating facility since it began operations in 1999. A number of modern
optical diagnostic instruments are hosted at remote sites as well as the
main transmitter facility, which has recently been expanded from the initial
960 kW prototype configuration to its full 3.6 MW design capability.
Upgrades to optical diagnostics have allowed a number of interesting new
observations to be made at the 960 kW power level since 2004. Systematic
beam-swinging experiments generating quantifiable levels of optical emission
at various regions in the sky for the first time clearly show that emission
intensity is very sensitive to distance from the magnetic zenith, and drops
off rapidly at about 15° zenith angle in directions other than magnetic
south. High temporal resolution measurements of emissions in the 557.7 nm
green line at start-up and in short transmitter pulses demonstrate that
localized irregularities are preferentially excited in the initial seconds
of heating, with evolution into a more homogenous spot occurring over a
period of about 1 min. High-quality emission altitude profiles at both
630.0 and 557.7 nm have recently been isolated from side-looking data,
spanning an altitude extent of over 200 km, which has allowed determination
of the effective lifetime of O (1D) over an unprecedented altitude
range. An innovative automated remote imager network utilizing low-cost
mirror optics has been designed and deployed to make such measurements
routinely. Observations of natural optical emissions at the site have
revealed the common presence of highly structured but faint co-rotating
subauroral precipitation that acts to suppress excitation of artificial F
region optical emissions in areas of active precipitation. The observed
spatial modulation of artificial optical emissions by structured
precipitation is consistent with localized absorption of HF waves in the
ionospheric D layer enhanced by the energetic particle precipitation.
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