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Model variant
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A model variant is one in which the values used in a parameterisation scheme has been changed from that used in the standard model. Hence it is possible (as in UKCP09) to build many different variants of a climate model in which parameter values are different (but plausible).
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In detail
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For a given model configuration there can be many model variants. This is because, irrespective of model configuration, it is necessary to parameterise
the model. The process of parameterising a model involves specifying
values in relationships between large scale and small scale processes, and these values may not be accurately
known, and thus may have a wide range of plausible values. This is one
source of modelling uncertainty known as parameter error. In UKCP09, this source of uncertainty is addressed by generating five different perturbed physics ensembles (PPE),
in which the model parameter values are assigned different values (but
within plausible limits), for each model variant. As a result, each
variant produces a different climate
projection. Each model variant is a member of the PPE.
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Find out more
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- Chapter 3 of the Climate Change Projections report.
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