High resolution spectroscopy of oxygen u.v. airglow

Abstract

Ultraviolet spectra of the oxygen airglow and related visible emission features have been regularly measured for a period of 2 years from a site outside Stockholm, Sweden (59°N, 18°E). The instrumentation includes a 1 m Ebert-Fastie scanning spectrometer for high resolution (1.3 Å) measurements and a six channel filter photometer. The high resolution measurements were confined to three spectral regions, each 130 Å in extent. The filter photometers monitored the following airglow features: OI green line, O 2 Atmospheric Band (0,1), O 2 Herzberg I, airglow continuum at two wavelengths and 546 nm mercury line. High resolution spectra containing a mixture of O 2 Herzberg I, Herzberg II and Chamberlain bands have been obtained under varying geophysical conditions. Analysis of these spectra is undertaken using a non-linear least-squares fitting technique allowing separation of individual bands. The O 2 Herzberg I total system intensity, as derived from the (6,7) band, changes in an almost linear manner with the green line. The details of the co-variation support a direct excitation mechanism rather than an indirect process proposed to overcome the apparent disagreement between laboratory and rocket measurement. Intensity variations of factor of 10 on a scale of days and a factor of two within a single night have been measured, which imply changes in the atomic oxygen densities of at least a factor of three.