Aspect angle sensitivity of pump-induced optical emissions at EISCAT

Abstract

We investigate the aspect angle sensitivity of the pump-induced artificial optical emissions in the ionosphere over the European Incoherent Scatter Scientific Association (EISCAT) high-frequency transmitter facility at Ramfjord, Norway, as a function of the pump beam launch angle relative to the magnetic field line direction. The highest intensity optical emissions occur when the pump beam pointing direction is in the magnetic zenith (approximately 12°S of local zenith). For pump beam directions further north from field aligned, the optical emission intensity decreases for the same pump power. In addition, the primary photon-emitting region becomes displaced towards the magnetic zenith relative to the pump beam and for larger aspect angles, the brightest emissions were found to be outside the −3-dB pump beam width. The Cooperative UK Twin-Located Auroral Sounding System (CUTLASS) coherent scatter high-frequency (HF) radar detected a quasi-constant level of backscatter power from the pumped ionosphere, indicating that saturated striations were formed for all pump beam directions. This indicates that the presence of upper-hybrid resonance is not sufficient to explain the angular sensitivity of the optical emissions.

Past, Present and Future of Active Radio Frequency Experiments in Space

“…Outside this angular range, optical emissions were effectively not observed. Kosch et al [2014a] confirmed this scenario at EISCAT, and likewise Shindin et al [2015] at SURA, albeit for a more limited region around the magnetic zenith. Kosch et al [2014a] also found that the optical emission always maximized in the magnetic zenith provided any pump power went in this direction.…”

“…Kosch et al [2014a] confirmed this scenario at EISCAT, and likewise Shindin et al [2015] at SURA, albeit for a more limited region around the magnetic zenith. Kosch et al [2014a] also found that the optical emission always maximized in the magnetic zenith provided any pump power went in this direction. Consistent with the optical observations, the pump-induced electron temperature enhancements, observed by the EISCAT incoherent scatter radar, also maximized in the magnetic zenith [Rietveld et al, 2003].…”

Large ionospheric disturbances produced by the HAARP HF facility

“…The upper atmospheric science community has access to a large number of high power HF transmitters used to modify the F region ionosphere. These include SURA in Russia [ Belikovich et al, ], European Incoherent Scatter (EISCAT) Heating in Norway [ Kosch et al, ], and the soon to be operational Arecibo HF facility in Puerto Rico. Each facility has unique capabilities because of their location with ambient electron densities that tend to be larger at lower latitudes and the inclination of the magnetic field which ranges from horizontal at the equator to nearly vertical at high latitudes.…”

New capabilities of the upgraded EISCAT high‐power HF facility

“…Another significant discovery was the fact that several HF‐induced phenomena in the F region are especially strong when pumping in the magnetic field‐aligned direction. For example, the optical emissions [ Kosch et al ., , ], electron heating [ Rietveld et al ., , ], and ion upwelling [ Kosch et al ., ] all are strongest when the HF beam is pointed along the magnetic field. The discovery of artificial ionization in recent years, which at HAARP has been detected as artificial layers, is discussed in detail by Mishin et al .…”