Upper atmospheric oxygen density determined from combined optical and incoherent scatter radar measurements

A comprehensive understanding of upper atmospheric dynamics requires an accurate knowledge of the density of atomic oxygen ( (O)), the major chemical species. Unfortunately, existing techniques to sense this important quantity remotely are generally unreliable, and investigations of atmospheric and ionospheric phenomena have been hampered by the need to rely on model predictions. In this dissertation, a technique is developed for passive measurement of the density of atomic oxygen near 300 km altitude, from ground-based observations of the O I 8446 A airglow emission.; This dissertation begins with the development and implementation of a Fabry-Perot interferometer capable of measuring this faint airglow emission in the nighttime sky. Observations were made of the O I 8446 A intensity, during several campaigns spanning a three-year period, from both the Millstone Hill (MA) and Arecibo (PR) observatories. These 8446 A measurements reveal that photoelectron impact on atomic oxygen is the only mechanism important in the production of this emission feature, and that current photoelectron models incorrectly predict the photoelectron flux during twilight and nighttime hours. An empirical correction is derived from the 8446 A measurements to correct this model shortcoming that can be easily incorporated into any photoelectron model.; From the observations gathered as part of this dissertation, the behavior of (O) at Millstone Hill is first determined, then examined under magnetic storm conditions. The results indicate that the upper atmosphere exhibits a tendency to significantly increase in density between midnight and sunrise. Coupled O I 6300 A and incoherent scatter radar observations show this density increase is not limited to (O) but can include (O{dollar}sb2{dollar}) (molecular oxygen) and (N{dollar}sb2{dollar}) (molecular nitrogen) as well. Further, this behavior is seen to be in agreement with current atmospheric models that predict a morning density increase as a result of high-latitude heating coupled with a south-ward surge in the neutral wind occurring shortly after midnight. These results show that model predictions of (O), even at middle latitudes, often underestimate morning densities and the effects of magnetic storms on upper atmospheric composition.