Towards a self consistent picture of odd nitrogen and molecular oxygen chemistry in the thermosphere

Details Towards a self consistent picture of odd nitrogen and molecular oxygen chemistry in the thermosphere Towards a self consistent picture of odd nitrogen and molecular oxygen chemistry in the thermosphere

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusmsa33b..04s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA33B-04

Physics

0300 Atmospheric Composition And Structure, 0355 Thermosphere: Composition And Chemistry, 0358 Thermosphere: Energy Deposition (3369)

Scientific paper

Recent observations by the technique of FUV solar occultation have provided new information on the variation of the O2 density in the mid thermosphere (140-200 km) with respect to solar activity. Surprisingly, at the highest levels of solar activity, the mid thermospheric O2 is less than at solar minimum. Such a variation is inconsistent with expectations based upon thermal expansion of the atmosphere and diffusive equilibrium, but is suggestive of a chemical sink for O2 that is more rapid at high levels of solar activity. The dominant chemical loss for mid-thermospheric O2 is oxidation by atomic nitrogen, both the ground state N4S and the excited state N2D. Since these reactions produce nitric oxide (NO), a consideration of O2 chemistry also needs to account for observed profiles of NO and atomic nitrogen. Here we use two photochemical models of the thermosphere to address this question. One model uses NRLMSIS to specify the O2 and then calculates odd nitrogen profiles which can be compared with specific observations. We use this to compare with rocket profiles of NO and a satellite measurement of the FUV spectrum of atomic nitrogen. The second model is a global mean model of thermosphere. It is used to calculate the O2 profile for solar maximum and solar minimum. Taken together, we use these models to evaluate the consistency of the odd nitrogen kinetic scheme with our understanding of O2 chemistry. Our results suggest that the temperature dependence of the oxidation of O2 by atomic nitrogen is a critical parameter to quantify. Also, the sources of atomic nitrogen from N2 dissociation need better understanding.

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