Spatiotemporal evolution of radio wave pump‐induced ionospheric phenomena near the fourth electron gyroharmonic

Abstract

[1] On 12 November 2001, the European Incoherent Scatter (EISCAT) high-frequency (HF) radio wave transmitter facility, operating in O-mode at 5.423 MHz with 550 MW effective radiated power, produced artificial optical rings which appeared immediately at transmitter turn-on and collapsed into blobs after $60 s while descending in altitude. A similar descent in altitude was observed in the EISCAT ultra high frequency (UHF) ion line enhancements. Likewise, the stimulated electromagnetic emission (SEE) spectra changed as the pump frequency approached the fourth electron gyroharmonic due to pump-induced variations in electron concentration. Optical recordings were made from Skibotn at 630.0 and 557.7 nm and from Ramfjord in white light. The altitude of the initial optical ring and steady state blob has been estimated by triangulation. The evolution in altitude of the optical emissions, ion line enhancements, and SEE spectra all show a similar morphology but are generally not at exactly the same height. Typically, the optical height is close to and a few kilometers below that of the radar backscatter but sometimes above it, both of which are above the SEE generation altitude. There is evidence that upper hybrid (UH) waves, which propagate perpendicular to the magnetic field line, and Langmuir (L) waves, which propagate parallel to the magnetic field line, act simultaneously to accelerate electrons even in the steady state.

Phenomena induced by powerful HF pumping towards magnetic zenith with a frequency near the F-region critical frequency and the third electron gyro harmonic frequency

“…Gurevich et al (2001Gurevich et al ( , 2002 proposed a magnetic zenith mechanism for making a large fraction of the ERP available in the plasma production region, and means for the electron acceleration. Bernhardt et al (1989), Djuth et al (1999) Pedersen et al (2003, Gustavsson et al (2005), Holma et al (2006), Ashrafi et al (2007) have also worked on electron acceleration mechanisms and experimental evidence for their presence. Our work here shows the signatures of the magnetic zenith mechanism in terms of both rapid formation of striations and strong Langmuir turbulence when the plasma-density enhancements were produced.…”

“…We should acknowledge that invoking the above explanations need not exclude other electron acceleration processes from occurring as well. For example, Ashrafi et al (2007) suggested that upper hybrid waves, which propagate perpendicular to the magnetic field, and Langmuir waves, which propagate parallel to the magnetic field, act simultaneously to accelerate electrons even in the steady state. However the role of Langmuir turbulence near the reflection height in electron acceleration remains central.…”

“…Spatio-temporal evolution of HF-induced phenomena near the fourth electron gyroharmonic (Ashrafi et al, 2006(Ashrafi et al, , 2007 is indicative of a descent in altitude of EISCAT UHF ion line enhancements and optical emissions, both accompanied by pump-induced variations in electron density.…”

Simulation study of the large-scale modification of the mid-latitude F-layer by HF radio waves with different powers

“…In particular, many experimental studies have been applied to the large-scale F-region modification by powerful HF radio waves and many interesting results were obtained (Utlaut and Violette, 1974;Gordon and Carlson, 1974;Mantas et al, 1981;Jones et al, 1986;Djuth et al, 1987;Duncan et al, 1988;Hansen et al, 1992;Mantas, 1994;Honary et al, 1995;Robinson et al, 1996;Frolov et al, 1997;Gustavsson et al, 2001;Rietveld et al, 2003;Ashrafi et al, 2007;Clausen et al, 2008;Pedersen et al, 2008). It turns out that significant variations in the electron temperatures and densities can be produced by powerful HF waves in the F-layer.…”

“…It is doubtful that the EAP value of 100 MW is attainable for the existing high-power radio wave heaters, in particular for the "Sura" heating facility (Nizhny Novgorod, Russia) whose effective radiated power (ERP) varies between 150 and 280 MW (Belikovich et al, 1999). Nevertheless, it is not impossible that the EAP value of 100 MW may be acquired in the future with the help of some mid-latitude ionospheric heater.…”