Abstract:
© 2015, Springer Science+Business Media New York. We present the results of analysis of the dependence of the ionospheric airglow in the red (630 nm) and green (557.7 nm) lines of atomic oxygen on the pump-wave frequency f<inf>0</inf> near the fourth electron gyroharmonic 4f<inf>ce</inf>. The experimental data were obtained in 2012 using the SURA heating facility. Stimulated electromagnetic emission spectra were used to determine the relation between f<inf>0</inf> and 4f<inf>ce</inf>. It is found that at f<inf>0</inf> > 4f<inf>ce</inf> and δf = f<inf>0</inf> − 4f<inf>ce</inf> ≈ 15–20 kHz the red-line airglow intensity is about a factor of 1.5 higher for the magnetic zenith pumping (when the pump beam is inclined 12° south of the magnetic field direction) than for the vertical pumping. In the green line for the same offsets δf, the airglow was recorded with confidence only during magnetic zenith pumping. During vertical pumping, no regular dependence of the red-line airglow intensity on δf in the range −15 < δf < 280 kHz was obtained, while the green-line airglow was observed at 15 < δf < +5 kHz and 230 < δf < 280 kHz. In the red line during vertical pumping, a change from the artificial airglow generation to the ionospheric background suppression was detected when the F-layer cutoff frequency was decreased. During magnetic zenith pumping, a wide (about 30°) background suppression zone was observed around the airglow spot with an about 6° angular width.
