THE SOLAR LY-ALPHA LINE-PROFILE

Solar Ly alpha irradiance measurements from the SOLar STellar Irradian ce Comparison Experiment (SOLSTICE) on the Upper Atmosphere Research S atellite (UARS) have been made since 1991 October with a spectral reso lution of 0.1 nm. The uniqueness of the small molecular oxygen cross s ection near Ly alpha permits the Ly alpha radiation to penetrate much deeper into the atmosphere than the other emissions near Ly alpha. We have taken advantage of this phenomenon by performing solar occultatio n experiments near Ly alpha to evaluate precisely the instrument scatt ered light contribution. After correcting for scattered light, the bro ad wings of the solar Ly alpha line can be extracted out to 5 nm from line center with a typical accuracy of +/-20%. The variability in the Ly alpha wings near 2 nm from line center is about one-half that of th e Ly alpha core emission, defined within 0.1 nm from line center. Thes e Ly alpha profile measurements are found to be consistent with the Sk ylab radiance measurements and theoretical models of the Ly alpha line profile computed using partial redistribution of photons in the sourc e function.