February 28, 2007
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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 11, NUMBER 9, SEPTEMBER 1998
ATMOSPHERIC CHEMISTRY AND DYNAMICS
Mass-Independent Oxygen Isotope Fractionation in Atmospheric CO as a
Result of the Reaction CO + OH, T. Röckmann et al.,Science
281, 544-546 (July 24, 1998).
Atmospheric CO exhibits isotope-fractionation effects that are not
related to the mass of the substituted isotope. Excess 17O was
detected in atmospheric CO at high northern latitudes during the summer.
This excess 17O ranged up to 7.5o/oo.
The excess results from the reaction CO + OH ®
CO2 + H, which is the most common reaction of CO in the
atmosphere. The surviving CO exhibits the excess, meaning that the
reaction with OH demonstrates a preference for CO with 18O
over that with 17O, raising fundamental questions about the
kinetic processes involved. No theoretical explanation is known to explain
this selective process. A similar effect also occurs in the formation of
ozone, where the reaction 16O + 18O18O
occurs 50% more readily than the reaction 18O + 16O16O.
The anomaly does make the concentration of C17O a good marker
for the age of CO in the atmosphere.
Seasonal Cycles and QBO Variations in Stratospheric CH4
and H2O Observed in UARS HALOE Data, W. J. Randel et al., J.
Atmos. Sci. 55 (2), 163-185 (1998).
Stratospheric methane and water vapor were measured from 1991 to 1997
during the Halogen Occultation Experiment that employed the Upper
Atmosphere Research Satellite. The data reveal latitudinal gradients in
atmospheric mixing in the subtropics and across the polar vortices. They
indicate a strong descent inside the polar vortices during winter and
spring. And they show a strong seasonal upwelling in the tropical upper
atmosphere associated with the semiannual oscillation. All of these
findings are in agreement with the processes of the mean meridional
circulation as understood from stratospheric meteorological analyses. Most
of the variance in interannual variations is related to the equatorial
quasibiennial oscillation, which also affects the latitudinal position of
the tropical reservoir in the middle atmosphere.
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