Abstract
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.
Highlights
The High Frequency Active Auroral Research Program (HAARP) has operated an ionospheric heating facility in Gakona, Alaska (62.4◦ N 145◦ W, ∼63◦ magnetic) since 1999
The main HF transmitter, or Ionospheric Research Instrument (IRI), in initial prototype configuration consisted of an array of 6×8 crossed dipoles providing 960 kW total power, with nominal effective radiated power (ERP) ranging from 10.8 MW at 2.8 MHz to 260 MW at 10 MHz
Optical imaging at HAARP had previously been limited to frame rates of ∼10 s or greater due to sensitivity, readout and housekeeping requirements on the various imager systems, but in light of some 2005 results showing beam-filling green line emissions collapsing into the magnetic zenith spot during the first ∼1 min of heating (Kosch et al, 2007a), which suggested an possible explanation for the green line onset delay first observed in 2002 (Pedersen et al, 2003), a concentrated effort to image the development of the emissions at higher time resolution was made in the most recent 2006 optical campaign
Summary
The High Frequency Active Auroral Research Program (HAARP) has operated an ionospheric heating facility in Gakona, Alaska (62.4◦ N 145◦ W, ∼63◦ magnetic) since 1999. The HAARP imager is a telecentric system utilizing 3.5 narrow-band (2 nm) filters feeding a recently upgraded 1 thermo-electrically cooled bare CCD camera It can be operated with either a fish-eye lens for all-sky coverage or placed on a mount and equipped with a 16◦ lens for higher resolution observations of optical emissions within the HAARP beam. In the sections that follow, we present and discuss observations made since 2004, when a variety of new and interesting features in both artificial and natural optical emissions have been observed, many resulting from the combination of improved optical instruments and the highly efficient 2nd gyroharmonic resonance Many of these observations are unique, depending upon capabilities or modes not available at other ionospheric heaters or resulting from interactions with the unique local environment
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