Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa51a1609m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SA51A-1609
Other
[0340] Atmospheric Composition And Structure / Middle Atmosphere: Composition And Chemistry, [0341] Atmospheric Composition And Structure / Middle Atmosphere: Constituent Transport And Chemistry, [3332] Atmospheric Processes / Mesospheric Dynamics, [3334] Atmospheric Processes / Middle Atmosphere Dynamics
Scientific paper
The distribution and partitioning of all hydrogen-carrying species in and above the mesosphere inform our understanding of upper atmospheric chemistry and transport; however, many species are not easily measured. Molecular hydrogen (H2) is described as a mesospheric reservoir of hydrogen atoms released from methane (CH4) oxidation and water vapor (H2O) photolysis. Only limited indirect measurements and modeling studies have provided evidence for this reservoir until now. Measuring air that descends from upper levels within polar stratospheric vortices provides a unique opportunity to sample the chemical composition of the mesosphere at more accessible stratospheric altitudes. Such measurements were made of atmospheric H2 by the balloonborne, in situ Lightweight Airborne Chromatograph Experiment (LACE) instrument during the 1999-2000 SAGE III Ozone Loss and Validation Experiment (SOLVE). Vertical profiles of a number of tracers were made in November 1999 after the vortex formation and again in March 2000 just before vortex breakup. The tropospheric-stratospheric H2 profile shifted dramatically from being vertically uniform (~0.5 ppm) in the young vortex to exhibiting distinct minimum (~0.4 ppm) and maximum (~1 ppm) peak features after a winter of mixing and descent in the late polar vortex. Both observational and model results show that a significant fraction of mesospheric air was present in the late vortex, suggesting that the late vortex H2 features were of mesospheric origin. The goal of this study is to determine whether the chemical measurements made with LACE confirm the anticipated H2 mixing ratio peak in the mesosphere. Tracer-tracer interrelationships of H2 with concurrently measured tracers, such as SF6, CO, N2O, and CFCs, are used to determine the original altitude and mixing ratio of the H2 peak. A simple model of mixing and descent within the vortex will be used to infer the altitude distribution of H2 in the mesosphere by forcing its consistency with other measured tracers. Agreement of the results with extant numerical projections and indirect measurements is discussed. Further characterization of the mesospheric reservoir of hydrogen may contribute to the understanding of atomic H in the thermosphere and beyond.
Meredith L. K.
Moore F. L.
Plumb Alan R.
Ray Allison E.
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