Three-dimensional simulation of stratospheric gravitational separation using the NIES global atmospheric tracer transport model
2018
Abstract. A three-dimensional simulation of gravitational separation, defined as the
process of atmospheric molecule separation under gravity according to their
molar masses, is performed for the first time in the upper troposphere and
lower stratosphere. We analyze distributions of two isotopes with a small
difference in molecular mass ( 13 C 16 O 2 ( M i =45 ) and
12 C 16 O 2 ( M i =44 )) simulated by the National Institute for
Environmental Studies (NIES) chemical transport model (TM) with a
parameterization of molecular diffusion. The NIES model employs global
reanalysis and an isentropic vertical coordinate and uses optimized
CO 2 fluxes. The applicability of the NIES TM to the modeling of
gravitational separation is demonstrated by a comparison with measurements
recorded by high-precision cryogenic balloon-borne samplers in the lower
stratosphere. We investigate the processes affecting the seasonality of
gravitational separation and examine the age of air derived from the tracer
distributions modeled by the NIES TM. We find a strong relationship between
age of air and gravitational separation for the main climatic zones. The
advantages and limitations of using age of air and gravitational separation
as indicators of the variability in the stratosphere circulation are
discussed.
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