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| Titel |
An efficient method to generate a perturbed parameter ensemble of a fully coupled AOGCM without flux-adjustment |
| VerfasserIn |
P. J. Irvine, L. J. Gregoire, D. J. Lunt, P. J. Valdes |
| 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 ; 6, no. 5 ; Nr. 6, no. 5 (2013-09-10), S.1447-1462 |
| Datensatznummer |
250084986
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| Publikation (Nr.) |
 copernicus.org/gmd-6-1447-2013.pdf |
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| Zusammenfassung |
| We present a simple method to generate a perturbed parameter ensemble (PPE)
of a fully-coupled atmosphere-ocean general circulation model (AOGCM),
HadCM3, without requiring flux-adjustment. The aim was to produce an
ensemble that samples parametric uncertainty in some key variables and gives
a plausible representation of the climate. Six atmospheric parameters, a
sea-ice parameter and an ocean parameter were jointly perturbed within a
reasonable range to generate an initial group of 200 members. To screen out
implausible ensemble members, 20 yr pre-industrial control simulations
were run and members whose temperature responses to the parameter
perturbations were projected to be outside the range of 13.6 ± 2 °C,
i.e. near to the observed pre-industrial global mean, were
discarded. Twenty-one members, including the standard unperturbed model, were
accepted, covering almost the entire span of the eight parameters,
challenging the argument that without flux-adjustment parameter ranges would
be unduly restricted. This ensemble was used in 2 experiments; an 800 yr
pre-industrial and a 150 yr quadrupled CO2 simulation. The behaviour
of the PPE for the pre-industrial control compared well to ERA-40 reanalysis
data and the CMIP3 ensemble for a number of surface and atmospheric column
variables with the exception of a few members in the Tropics. However, we
find that members of the PPE with low values of the entrainment rate
coefficient show very large increases in upper tropospheric and
stratospheric water vapour concentrations in response to elevated CO2
and one member showed an implausible nonlinear climate response, and as
such will be excluded from future experiments with this ensemble. The
outcome of this study is a PPE of a fully-coupled AOGCM which samples
parametric uncertainty and a simple methodology which would be applicable to
other GCMs. |
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