SIMULTANEOUS RETRIEVAL OF THE SOLAR EUV FLUX AND NEUTRAL THERMOSPHERIC O, O2, N2, AND TEMPERATURE FROM TWILIGHT AIRGLOW

We present a method to retrieve neutral thermospheric composition and the solar EUV flux from ground-based twilight optical measurements of the O+(2P) 7320 angstrom and O(1D) 6300 angstrom airglow emissions. Th e parameters retrieved are the neutral temperature, the O, O2, N2 dens ity profiles, and a scaling factor for the solar EUV flux spectrum. Th e temperature, solar EUV flux scaling factor, and atomic oxygen densit y are first retrieved from the 7320-angstrom emission, which are then used with the 6300-angstrom emission to retrieve the O2 and N2 densiti es. The retrieval techniques have been verified by computer simulation s. We have shown that the retrieval technique is able to statistically retrieve values, between 200 and 400 km, within an average error of 3 .1 +/- 0.6% for thermospheric temperature, 3.3 +/- 2.0% for atomic oxy gen, 2.3 +/- 1.3% for molecular oxygen, and 2.4 +/- 1.3% for molecular nitrogen. The solar EUV flux scaling factor was found to have a retri eval error of 5.1 +/- 2.3%. All the above errors have a confidence lev el of 95%. The purpose of this paper is to prove the viability and use fulness of the retrieval technique by demonstrating the ability to ret rieve known quantities under a realistic simulation of the measurement process, excluding systematic effects.