High-latitude HF-induced airglow displaced equatorwards of the pump beam

HF-induced airglow at 630 nm was observed by the Digital All-sky Imager, lo cated near Skibotn in Norway, at F-region altitudes above the EISCAT HF fac ility near Tromso on 21 February 1999. The transmitter was operated in a 4- min on, 4-min off sequence at 4.04 MHz O-mode with the beam pointing vertic ally. The airglow reached a peak intensity of about 100 R above background and appeared equatorward of the HF beam's projection on the reflection alti tude, which was obtained from ionograms. Generally, the region of maximum a irglow was displaced towards the magnetic field line (zenith angle = 12.8 d egrees S) passing through Lire HF facility. This is a unique feature of the se observations. From mid-latitude studies, such airglow is thought to be e xcited either by electrons energised to several eV by plasma turbulence, or by thermal electron temperature enhancement. Such localisation towards the magnetic field is unexpected for both mechanisms of airglow generation and suggests this feature may be important at high latitudes.