First narrow-field Fabry-Perot interferometer observation of artificial airglow

Abstract:

Ground based narrow-field (field of view 1 degree of half angle) Fabry Perot interferometers (FPIs) have been used to determine wind speeds and temperatures from natural upper-atmospheric emissions such as airglow and aurora. FPI observations are typically limited to altitudes where natural emissions occur, yet natural emissions are largely lacking in the 120 to 200 km range. Although other observational techniques, such as in situ measurement via low earth orbiting satellite or sounding rocket, provide the possibility of short time scale observation in this range, long duration observations of these altitudes would be particularly interesting as it is part of the region of transition between the space like regime and the atmosphere like regime, termed the Space-Atmosphere Interaction Region (SAIR).

The High frequency Active Auroral Research Program (HAARP) located in Gakona, Alaska has an array of high-power HF radio transmitters (3.6 MW) capable of generating an artificial airglow patch in the 120-200 km altitude range that provides the same observational potential as naturally occurring airglow at 630 nm and 557 nm. FPIs at observation sites in Eagle, Alaska and Poker Flat, Alaska were adapted to capture simultaneous observation of the 630 nm red line emission in the artificial airglow. The first observations of artificial airglow with a narrow-field Fabry-Perot interferometer have been analyzed, examining emission intensity, line-of-sight wind speed, and temperature. Unfavorable conditions have prevented simultaneous two-site observation which would have resolved two-dimensional wind profiles. We will present these results and discuss them in relation to standard empirical thermospheric models.