Optical (λ6300) detection of radio frequency heating of electrons in theFregion

Abstract

In recent years methods of producing controlled modifications of the ionosphere by use of high‐intensity radio‐frequency waves have been proposed; some have been tried with inconclusive results. The present paper describes detection of significant (∼30%) changes in the electron temperature in the F2 region produced by absorption of radio‐frequency energy propagated at or near the local ionospheric plasma frequency. The radio‐frequency source is the 1‐Mw cw transmitter and ∼16° beamwidth antenna array described in the accompanying paper by Utlaut [1970]. As shown by the calculations of Meltz and LeLevier [1970], electron temperature increases of ∼35% can be expected within a few tens of seconds after the transmitter, tuned to within 1% of f0F2, is turned on.

Modifying the Ionosphere with Intense Radio Waves

“…Using X-mode excitation, Biondi et al (9) observed airglow from excited oxygen atoms at 6300 angstroms; these observations showed the predicted suppression of ambient intensity, as illustrated in Fig. 6 for a transmission cycle of 10 minutes on and 10 minutes off.…”

“…Techniques employed to date include the observation of atmospheric airglow emissions and the reflection and incoherent scattering of radio waves. Changes induced in airglow emissions (at 6300 angstroms) can be interpreted in terms of changes in the electron temperature, since the dissociative recombination rate of electrons and Q2+ ions (which produces the normal airglow) has an inverse temperature dependence (9 tion on variations in electron density. Measurement of relative radio-reflectivity was regarded as a technique that would provide information on changes in the electron temperature, since the reflectivity was expected to increase with electron temperature.…”

Heater‐induced ionization inferred from spectrometric airglow measurements

“…The production of enhanced optical airglow was one of the first phenomena to be associated with ionospheric modifications by high-power HF waves [Biondi et al, 1970;Haslett and Megill, 1974;Adeishvili et al, 1978] and continues to be a focus of research and attention (see review by Gurevich [2007]). While it was initially believed that the enhancements could be explained in terms of heating and the enhancement of the tail of the thermal electron population [Mantas, 1994;Mantas and Carlson, 1996], the measured ratios of red and green line emissions and the appearance of optical emissions with high-energy thresholds signaled the presence of a nonthermal component of the electron energy distribution [Bernhardt et al, 1989;Gustavsson et al, 2001Gustavsson et al, , 2003Djuth et al, 2005;Gustavsson et al, 2005].…”

The electron energy distribution during HF pumping, a picture painted with all colors

“…Ionospheric high frequency (HF, 3-30 MHz) radio waveinduced optical emissions have been studied since the early 1970s (Biondi et al, 1970;Haslett and Megill, 1974) at low (Bernhardt et al, 1988), middle (Bernhardt et al, 1989a) and auroral Kosch et al, 2000;Pedersen and Carlson, 2001) …”