Journal cover Journal topic
Advances in Statistical Climatology, Meteorology and Oceanography An international open-access journal on applied statistics
Adv. Stat. Clim. Meteorol. Oceanogr., 2, 17-37, 2016
https://doi.org/10.5194/ascmo-2-17-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
18 Apr 2016
Building a traceable climate model hierarchy with multi-level emulators
Giang T. Tran1, Kevin I. C. Oliver1, András Sóbester2, David J. J. Toal2, Philip B. Holden3, Robert Marsh1, Peter Challenor1,4, and Neil R. Edwards3 1Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, UK
2Faculty of Engineering and the Environment, University of Southampton, Southampton, UK
3Environment, Earth and Ecosystems, Open University, Milton Keynes, UK
4College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK
Abstract. To study climate change on multi-millennial timescales or to explore a model's parameter space, efficient models with simplified and parameterised processes are required. However, the reduction in explicitly modelled processes can lead to underestimation of some atmospheric responses that are essential to the understanding of the climate system. While more complex general circulations are available and capable of simulating a more realistic climate, they are too computationally intensive for these purposes. In this work, we propose a multi-level Gaussian emulation technique to efficiently estimate the outputs of steady-state simulations of an expensive atmospheric model in response to changes in boundary forcing. The link between a computationally expensive atmospheric model, PLASIM (Planet Simulator), and a cheaper model, EMBM (energy–moisture balance model), is established through the common boundary condition specified by an ocean model, allowing for information to be propagated from one to the other. This technique allows PLASIM emulators to be built at a low cost. The method is first demonstrated by emulating a scalar summary quantity, the global mean surface air temperature. It is then employed to emulate the dimensionally reduced 2-D surface air temperature field. Even though the two atmospheric models chosen are structurally unrelated, Gaussian process emulators of PLASIM atmospheric variables are successfully constructed using EMBM as a fast approximation. With the extra information gained from the cheap model, the multi-level emulator of PLASIM's 2-D surface air temperature field is built using only one-third the amount of expensive data required by the normal single-level technique. The constructed emulator is shown to capture 93.2 % of the variance across the validation ensemble, with the averaged RMSE of 1.33 °C. Using the method proposed, quantities from PLASIM can be constructed and used to study the effects introduced by PLASIM's atmosphere.

Citation: Tran, G. T., Oliver, K. I. C., Sóbester, A., Toal, D. J. J., Holden, P. B., Marsh, R., Challenor, P., and Edwards, N. R.: Building a traceable climate model hierarchy with multi-level emulators, Adv. Stat. Clim. Meteorol. Oceanogr., 2, 17-37, https://doi.org/10.5194/ascmo-2-17-2016, 2016.
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In this work, we combine the information from a complex and a simple atmospheric model to efficiently build a statistical representation (an emulator) of the complex model and to study the relationship between them. Thanks to the improved efficiency, this process is now feasible for complex models, which are slow and costly to run. The constructed emulator provide approximations of the model output, allowing various analyses to be made without the need to run the complex model again.
In this work, we combine the information from a complex and a simple atmospheric model to...
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