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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Development and technical paper
14 Feb 2017
Review status
A revision of this discussion paper was accepted for the journal Geoscientific Model Development (GMD) and is expected to appear here in due course.
Practice and philosophy of climate model tuning across six U.S. modeling centers
Gavin A. Schmidt1, David Bader2, Leo J. Donner3, Gregory S. Elsaesser1,4, Jean-Christophe Golaz2, Cecile Hannay5, Andrea Molod6, Rich Neale5, and Suranjana Saha7 1NASA Goddard Institute for Space Studies, 2880 Broadway, New York
2DOE Lawrence Livermore National Laboratory, Livermore, California
3GFDL/NOAA, Princeton University Forrestal Campus, 201 Forrestal Rd., Princeton, NJ 08540
4Columbia University, New York, NY 10025
5National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA,
6Global Modeling and Assimilation Office, NASA GSFC, Greenbelt, MD 20771
7Environmental Modeling Center, NCEP/NWS/NOAA, NCWCP College Park, MD 20740
Abstract. Model calibration (or "tuning") is a necessary part of developing and testing coupled ocean-atmosphere climate models regardless of their main scientific purpose. There is an increasing recognition that this process needs to become more transparent for both users of climate model output and other developers. Knowing how and why climate models are tuned and which targets are used is essential to avoiding possible misattributions of skillful predictions to data accommodation and vice versa. This paper describes the approach and practice of model tuning for the six major U.S. climate modeling centers. While details differ among groups in terms of scientific missions, tuning targets and tunable parameters, there is a core commonality of approaches. However, practices differ significantly on some key aspects, in particular, in the use of initialized forecast analyses as a tool, the explicit use of the historical transient record, and the use of the present day radiative imbalance vs. the implied balance in the pre-industrial as a target.

Citation: Schmidt, G. A., Bader, D., Donner, L. J., Elsaesser, G. S., Golaz, J.-C., Hannay, C., Molod, A., Neale, R., and Saha, S.: Practice and philosophy of climate model tuning across six U.S. modeling centers, Geosci. Model Dev. Discuss.,, in review, 2017.
Gavin A. Schmidt et al.
Gavin A. Schmidt et al.


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Short summary
The development of coupled ocean atmosphere climate models is a complex process that inevitably includes multiple calibration steps (sometimes called "tuning"). The tuning uses degrees of freedom allowed by uncertainties in model approximations to modify parameters and code to make the simulation better align with some selected observed target(s). We describe how the targets, tuning parameters and philosophy of tuning vary across 6 US modeling centers to aid transparency of this key element.
The development of coupled ocean atmosphere climate models is a complex process that inevitably...