An analysis of satellite observations of the O I EUV dayglow

Abstract

An analysis of satellite STP78‐1 measurements at solar maximum of the latitudinal variation of O I EUV dayglow emissions at 1356, 1304 and 989 Å is presented. The day glow intensity measurements corroborated by Atmosphere Explorer‐E data indicate that the exospheric temperature was about 220–240 K higher than predicted by the MSIS‐83 thermospheric model. In addition, the temperature variation with latitude is not as large as predicted by MSIS‐83 for day 80, 1979. The 1304‐ and 1356‐Å intensity measurements are consistent with electron impact excitation cross‐section measurements of Zipf and Erdman (1985). The 989‐Å excitation cross section of Zipf and Erdman (1985) requires a branching ratio of 7×10 −4 for transitions other than 989‐Å in order to produce agreement with our data. The Vaughan and Doering (1987) direct 3 s ' ³ D ° excitation cross section, about a factor of 3 smaller than the optical excitation cross section of Zipf and Erdman (1985), is also compatible with our 989‐Å data for a branching ratio near 1×10 −4 . The solar 1304‐Å spectral irradiance inferred from the observations is about a factor of 2 lower than the rocket measurements of Mount et al. (1980), but is consistent with Solar Mesosphere Explorer results. Our measurements also suggest that enhancement of the 1304‐Å electron impact excitation cross section due to radiative entrapment of cascade‐feeding photons is negligible.