Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa31a..05d&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SA31A-05
Physics
0310 Airglow And Aurora, 0355 Thermosphere: Composition And Chemistry
Scientific paper
Collisions of O with the trace species CO2 and NO provide significant atmospheric cooling in the Earth's upper mesosphere-lower thermosphere, between 70 and 200 km. These collisions efficiently populate CO2(ν 2) and NO(v=1), respectively, converting a portion of the ambient kinetic energy into 15-μ m and 5.3-μ m IR emission. Much of the emission escapes into space, effectively removing ambient kinetic energy from the atmosphere. In recent years our group has performed laboratory measurements to better characterize the vibrational energy transfer (VET) efficiencies for the NO-O system, and is currently developing techniques for studying VET in the CO2-O system. These results, together with TIME-GCM modeling, show that predictions of upper atmospheric temperature and density are sensitive to the values assumed for the NO-O and CO2-O VET efficiencies, including their temperature dependence. The predicted cooling rates may either add or compensate, depending on the atmospheric conditions and on the kinetic parameters used in the photochemical model. In particular, the large CO2-O VET efficiency and increasing global CO2 concentrations suggest that the thermosphere may be cooling and contracting over time. This hypothesis is supported by a limited number of analyses of satellite orbital motion, as well as variation in polar mesospheric cloud and ion layer altitudes implied by recent observations. This has important implications for photochemical models, radiance predictions, and for spacecraft drag and satellite longevity. It also provides an interesting connection between a molecular-level parameter, the CO2-O VET efficiency, and the macroscopic effects of atmospheric density and satellite drag.
Castle Karen J.
Dodd James A.
Hwang Eunsook S.
Sharma Ramesh D.
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