HR: 15:25h
AN: SA13B-08 INVITED     [Abstracts]
TI: Visible Region Dayglow as a Monitor of Thermospheric Solar Energy Deposition
AU: * Shepherd, G G
EM: gordon@yorku.ca
AF: Centre for Research in Earth and Space Science, York University, 4700 Keele Street, Toronto, ON M3J 1P3 Canada
AB: Dayglow is the short name for daytime airglow, the atmospheric emission produced by photochemical processes; i.e. by non-thermal means. It is observed in the ultraviolet and visible regions, as well as in the near-infrared. The nightglow is produced entirely by chemistry, through the recombination of ions and atoms that are formed in the daytime. The dayglow includes the same chemical processes, but as well includes "prompt" emission caused by the absorption of shorter-wavelength solar radiation, and is therefore a valuable monitor of the solar radiation in the corresponding spectral regions. The visible and near-IR dayglow can in principle be detected from the ground, but only with instrumentation capable of distinguishing it from the enormously stronger light scattered from the lower atmosphere. The Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite views visible region dayglow emission from above, at the Earth's limb, with a meter-long baffle that allows it to be measured above the intense light scattered from the lower atmosphere. The atomic oxygen "green line" emission from the O(1S) level, at 557.7 nm occurs in two distinct layers, one peaking near 160 km that is produced almost entirely through the absorption of solar EUV radiation and its subsequent processes, and another peaking near 105 km that is produced mainly by the absorption of solar Lyman-beta and the recombination of atomic oxygen. About one-half million WINDII green line profiles were acquired between 1992 and 1997. The lower layer is found to be enhanced during solar flares, almost certainly by x-rays. Thus the green line responds to at least three different regions of the solar spectrum. The transition from O(1D) at 630.0 nm has a single peak with an average altitude of about 250 km, and is a result mainly of excitation in the EUV. The dayglow response to the solar input is presented and characterized, and its contribution to the understanding of energy deposition in the thermosphere is described.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0310 Airglow and aurora
DE: 0335 Ion chemistry of the atmosphere (2419, 2427)
DE: 0355 Thermosphere--composition and chemistry
DE: 0358 Thermosphere--energy deposition
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting