HR: 15:15h
AN: SA33C-07    [Abstracts]
TI: Comparison of Column O/N2 From GUVI Limb Profiles and Disk Images
AU: * Stephan, A W
EM: andrew.stephan@nrl.navy.mil
AF: Space Science Division Naval Research Lab, 4555 Overlook Ave., SW, Washington, DC 20375, United States
AU: Meier, R R
EM: robert.meier@nrl.navy.mil
AF: Department of Physics and Astronomy George Mason University, 4400 University Dr. MS 3F3, Fairfax, VA 22030, United States
AB: We present the first statistical, direct comparison among column O/N₂ values obtained from GUVI limb profiles and disk-image measurements of the OI 135.6 nm and N₂ LBH emissions. In particular, we focus on geomagnetically quiet periods when the compositional structure of the thermosphere is uncomplicated and the measurement and analysis methods for both types of data should produce highly accurate values. Our comparisons of data from 2002-2005 show that limb-derived values are higher than disk-derived values by 5-10%. One possible cause for this difference is the value of the cross section for electron impact on N₂ that is the source of the LBH emission but has proved difficult to resolve between various measurements. Thermospheric O and N₂ profiles retrieved from limb airglow profiles have been found to be largely independent of this cross section, while the analysis of disk images to obtain column O/N₂ relies on knowledge of the absolute magnitude of the intensities and thus is dependent on the cross sections for electron impact on O and N₂. Our results from these years suggest the need to increase the cross section for N₂ LBH an additional 10-20% from the factor of 1.4 that is currently applied to the Ajello and Shemansky (1985) cross section in the analysis of the GUVI disk images that are available in the online data products. However, limb O/N₂ measurements during the solar minimum period of 2006 are lower than the disk values, suggesting a correlation may exist between the solar EUV and the determination of the LBH excitation cross section.
DE: 0310 Airglow and aurora
DE: 0355 Thermosphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: SPA-Aeronomy [SA]
MN: 2007 Fall Meeting