Thermospheric Composition and Solar EUV Flux from the Global-scale
Observations of the Limb and Disk (GOLD) mission
Abstract
Observations of far-ultraviolet (FUV) dayglow by the Global-scale
Observations of Limb and Disk (GOLD) mission provide a new opportunity
to monitor relative composition changes in the upper atmosphere as well
as solar extreme ultraviolet (EUV) variability. Relative composition
changes are quantified by ΣO/N2, the column density ratio of atomic
oxygen to molecular nitrogen, while QEUV provides a measure of the solar
EUV energy flux from 1 to 45 nm into the upper atmosphere. This spectral
range provides the ionizing radiation which ultimately results in FUV
airglow emission produced by photodissociation and photoelectron impact.
The quantities ΣO/N2 and QEUV are derived from GOLD FUV observations
through lookup tables that are constructed using a first-principles
photoelectron transport model. The two FUV emissions used are O I 135.6
nm and the N2 Lyman-Birge-Hopfield (LBH) bands. We present an overview
of the theoretical basis for the algorithms and practical considerations
for application to GOLD data. The effects of uncertainties in electron
impact cross sections, off-nadir viewing, and instrument artifacts are
reviewed. We also discuss GOLD Level 1C DAY, Level 2 data products ON2
and QEUV, and present representative samples of each.