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| Titel |
Evaluation of the new UKCA climate-composition model – Part 2: The Troposphere |
| VerfasserIn |
F. M. O'Connor, C. E. Johnson, O. Morgenstern, N. L. Abraham, P. Braesicke, M. Dalvi, G. A. Folberth, M. G. Sanderson, P. J. Telford, A. Voulgarakis, P. J. Young, G. Zeng, W. J. Collins, J. A. Pyle |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 1 ; Nr. 7, no. 1 (2014-01-10), S.41-91 |
| Datensatznummer |
250115531
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| Publikation (Nr.) |
 copernicus.org/gmd-7-41-2014.pdf |
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| Zusammenfassung |
| In this paper, we present a description of the tropospheric chemistry
component of the UK Chemistry and Aerosols (UKCA) model which has been
coupled to the Met Office Hadley Centre's HadGEM family of climate models. We
assess the model's transport and scavenging processes, in particular
focussing on convective transport, boundary layer mixing, wet scavenging and
inter-hemispheric exchange. Simulations with UKCA of the short-lived radon
tracer suggest that modelled distributions are comparable to those of other
models and the comparison with observations indicate that apart from a few
locations, boundary layer mixing and convective transport are effective in
the model as a means of vertically redistributing surface emissions of radon.
Comparisons of modelled lead tracer concentrations with observations suggest
that UKCA captures surface concentrations in both hemispheres very well,
although there is a tendency to underestimate the observed geographical and
interannual variability in the Northern Hemisphere. In particular, UKCA
replicates the shape and absolute concentrations of observed lead profiles, a
key test in the evaluation of a model's wet scavenging scheme. The timescale
for inter-hemispheric transport, calculated in the model using a simple
krypton tracer experiment, does appear to be long relative to other models
and could indicate deficiencies in tropical deep convection and/or
insufficient boundary layer mixing. We also describe the main components of
the tropospheric chemistry and evaluate it against observations and other
tropospheric chemistry models. In particular, from a climate forcing
perspective, present-day observed surface methane concentrations and
tropospheric ozone concentrations are reproduced very well by the model,
thereby making it suitable for long centennial integrations as well as
studies of biogeochemical feedbacks. Results from both historical and future
simulations with UKCA tropospheric chemistry are presented. Future
projections of tropospheric ozone vary with the Representative Concentration
Pathway (RCP). In RCP2.6, for example, tropospheric ozone increases up to
2010 and then declines by 13% of its year-2000 global mean by the
end of the century. In RCP8.5, tropospheric ozone continues to rise steadily
throughout the 21st century, with methane being the main driving factor.
Finally, we highlight aspects of the UKCA model which are undergoing and/or
have undergone recent developments and are suitable for inclusion in a
next-generation Earth System Model. |
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