Optical and ionospheric phenomena at EISCAT under continuous X‐mode HF pumping

N F Blagoveshchenskaya,M Kosch,T K Yeoman,T Sergienko,U Brändström,I Häggström,T D Borisova

doi:10.1002/2014ja020658

Abstract

AbstractWe present experimental results from multiinstrument observations in the high‐latitude ionospheric F2 layer at the EISCAT (European Incoherent Scatter Scientific Association) heating facility. The results come from a set of experiments, when an X‐polarized HF pump wave at high heater frequencies (fH > 6.0 MHz) was injected into the F region of the ionosphere toward the magnetic zenith. Experiments were carried out under quiet magnetic conditions with an effective radiated power of 458–548 MW. HF pumping was produced at different heater frequencies, away from electron gyroharmonic frequencies, and different durations of heater pulses. We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high‐latitude ionospheric F2 layer induced by an X‐polarized HF pump wave. Intensities at red and green lines varied in the range 110–950 R and 50–350 R, respectively, with a ratio of green to red line of 0.35–0.5. The results of optical observations are compared with behaviors of the HF‐enhanced ion and plasma lines from EISCAT UHF incoherent scatter radar data and small‐scale field‐aligned artificial irregularities from Cooperative UK Twin Located Auroral Sounding System observations. It was found that the X‐mode radio‐induced optical emissions coexisted with HF‐enhanced ion and plasma lines and strong artificial field‐aligned irregularities throughout the whole heater pulse. It is indicative that parametric decay or oscillating two‐stream instabilities were not quenched by fully established small‐scale field‐aligned artificial irregularities excited by an X‐mode HF pump wave.

Highlights

As a general rule, powerful HF radio waves with the ordinary polarization (O mode) are used for the modification of the F region of the ionosphere
We show the first experimental evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the high-latitude ionospheric F2 layer induced by an X-polarized HF pump wave
In this paper we show the first evidence of the excitation of artificial optical emissions at red (630 nm) and green (557.7 nm) lines in the ionospheric F2 layer at the EISCAT heating facility induced by an X-polarized HF pump wave at high heater frequencies, radiated parallel to the magnetic field direction

Summary

Introduction

Powerful HF radio waves with the ordinary polarization (O mode) are used for the modification of the F region of the ionosphere. Nonlinear interaction between powerful HF radio waves with the ordinary polarization (O mode) and the F2 layer ionosphere plasma produces a large number of phenomena which are well documented [Robinson, 1989; Gurevich, 2007, and references therein]. The excitation of radio-induced optical emissions (RIOEs) is one of the impressive phenomena observed from HF modification experiments. The most common RIOEs, such as the red (630 nm) and green (557.7 nm) lines, were observed at different HF heating facilities at middle and high latitudes [see, for example, Bernhardt et al, 1989; Brändström et al, 1999; Gustavsson et al, 2001, 2002; Pedersen and Carlson, 2001; Pedersen et al, 2003, 2009; Kosch et al, 2007a; Gustavsson and Eliasson, 2008]. The strongest artificial emissions are excited during HF pumping in the magnetic field-aligned direction [Gurevich et al, 2002; Pedersen et al, 2003; Rietveld et al, 2003; Mishin et al, 2005a]

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Results

Conclusion