Atomic oxygen densities retrieved from Optical Spectrograph and Infrared Imaging System observations of O2 A-band airglow emission in the mesosphere and lower thermosphere

Atomic oxygen densities, [O], have been retrieved from Optical Spectrograph and Infrared Imaging System (OSIRIS) observations of the O-2 (b(1)Sigma(+)(g), v' = 0 - X-3 Sigma(+)(g), v '' = 0) A-band airglow emission in the mesosphere and lower thermosphere. Daytime atomic oxygen densities, [O], have been inferred from ozone densities, [O-3], that were retrieved from OSIRIS O-2 A-band dayglow observations, and nighttime [O] have been retrieved directly from A-band nightglow observations employing an iterative-Newtonian optimal estimation inversion technique. Low-latitude results from 2007-2009 are presented and discussed. Variations in [O] between daytime (early morning, similar to 0700 LT) and nighttime (late evening, similar to 1900 LT) are shown to be strongly altitude dependent, with average nighttime densities in the tropics larger than daytime densities by similar to 10% at 95 km and by more than a factor of 4 at 85 km. Seasonal variations in [O] are also examined and indicate that the seasonal variations of [O] are strongly influenced by the local photochemistry and are less dependent on dynamical variations. OSIRIS measurements are also compared to [O] predicted by the NRL-MSISE-00 model. The comparisons show that the derived OSIRIS densities are up to an order of magnitude larger than the MSIS values and that the seasonal oscillations of MSIS [O] are 180 degrees out of phase with the OSIRIS measurements.