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| Titel |
CO2 seasonal variations in the UT/LS region as observed by CONTRAIL and four transport models |
| VerfasserIn |
Yosuke Niwa, Yousuke Sawa, Prabir Patra, Toshinobu Machida, Hidekazu Matsueda |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049680
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| Zusammenfassung |
| The upper troposphere (UT) and lower stratosphere (LS) is crossroad of tropospheric air
pollution and photochemically produced species in the stratosphere. It is thus important to
understand the stratosphere—troposphere exchange (STE) processes that allow
transport of chemical species across the tropopause. Recently, transport of chemically
and radiatively active short-lived species, such as water vapour, sulphur species,
halogenated compounds and aerosols from troposphere to stratosphere has been
studied in greater details using atmospheric transport models. Here we used carbon
dioxide (CO2) as a tracer of the interest, which is no photochemical loss/production
in both troposphere and stratosphere and has very strong seasonality in surface
fluxes, to analyze the role of surface fluxes and UT/LS transport processes in tracer
distribution.
We used atmospheric CO2 observations from the Comprehensive Observation Network
for Trace gases by Airliner (CONTRAIL) project. In CONTRAIL project, high-frequency
and wide-ranging CO2 data in the UT/LS region have been obtained by Continuous CO2
Measuring Equipment (CME) aboard commercial aircraft of Japan Airlines (JAL). Transport
simulations of atmospheric CO2 were performed by four global chemical transport
models (ACTM, MJ98-CDTM, NICAM-TM, NIES) using common CO2 fluxes. The
model simulations were first sampled along the individual CONTRAIL flight tracks
and then monthly means were constructed. The simulated and CONTRAIL CO2
concentrations for the period of 2006—2007 were then converted to equivalent latitude and
potential temperature coordinate system for analyzing the UT/LS distribution. In the
previous study, the models were evaluated for surface CO2 concentrations and vertical
profiles over the airport, which showed satisfactory results. However, transport model
abilities to simulate the CO2 distributions in the UT/LS region have been not fully
understood.
During winter—spring, all the models successfully reproduced longitudinal CO2
variations along the flight paths. Although the magnitudes of the gradients are underestimated
in some cases, the patterns of longitudinal variations are mutually similar. On the other hand,
in July, some models produced consistent longitudinal variations, meanwhile those simulated
by the other models are almost flat. This fact suggests that producing longitudinal variations
is more difficult in summer than in winter—spring. Comparison of CO2 distributions over
flight paths between Japan and Europe in the common equivalent latitude—potential
temperature coordinate shows that the models reproduced observed CO2 distributions
following the tropopause in winter—spring. The CO2 gradients across the tropopause are
underestimated by approximately 2 ppm between Î = 300 K and Î = 350 K surfaces.
In summer, the isentropic transport of high CO2 from the upper-troposphere in
lower latitudes to the lower-stratosphere in higher latitudes were well simulated
by the models, though significant differences in CO2 across Î = 340 K surfaces
persist. |
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