Metallic Layers in the Mesopause and Lower Thermosphere Region

Details Metallic Layers in the Mesopause and Lower Thermosphere Region Metallic Layers in the Mesopause and Lower Thermosphere Region

Jan 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999adspr..24.1559p&link_type=abstract

Advances in Space Research, Volume 24, Issue 11, p. 1559-1570.

Computer Science

25

Scientific paper

The layers of neutral metal atoms such as Na and Fe, which occur in the mesosphere and lower thermosphere as a result of meteoric ablation, can be observed with excellent spatial and temporal resolution by lidar. This has proved to be a powerful technique for studying dynamical processes between 80 and 105 km. However, an important assumption has been that these metal atoms behave as chemically inert tracers. The validity of this depends on the kinetic response of the metal atoms and their compounds to dynamical perturbations in both the temperature and the concentrations of minor species such as O3, H2O, O and H. This paper describes laboratory studies of several important reactions involving Na and Fe species. The reaction NaHCO3 + H -> Na + H2O + CO2 was investigated using a fast flow tube, where sodium bicarbonate was produced in situ from a flow of Na vapour mixed sequentially with N2O, H2 and CO2, and then reacted with an excess of atomic H. The results appear to provide complete closure for the upper mesospheric chemistry of sodium. The reactions of FeO with O3, O2, H2O and CO2 were studied by the pulsed laser photolysis of a ferrocene/NO2 mixture, followed by time-resolved laser induced fluorescence of FeO. The resulting rate coefficients, together with ab initio quantum calculations on the Fe-containing species formed by these reactions, indicate that FeO3 is probably the most important reservoir for iron immediately below the atomic Fe layer. A wave-driven model was then employed to compare Na and Fe as dynamical tracers. This shows that, whereas Na is essentially conserved as a tracer between 80 and 105 km, Fe could undergo significant chemical amplification of dynamical perturbations below 87 km, especially during summer. Differences in the ion-molecule chemistries of these metals indicate that the Fe/Na ratio should exhibit large wave-driven perturbations above 100 km

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