Articles | Volume 10, issue 9
Geosci. Model Dev., 10, 3207–3223, 2017
Geosci. Model Dev., 10, 3207–3223, 2017

Review and perspective paper 01 Sep 2017

Review and perspective paper | 01 Sep 2017

Practice and philosophy of climate model tuning across six US modeling centers

Gavin A. Schmidt1, David Bader2, Leo J. Donner3, Gregory S. Elsaesser1,4, Jean-Christophe Golaz2, Cecile Hannay5, Andrea Molod6, Richard B. Neale5, and Suranjana Saha7 Gavin A. Schmidt et al.
  • 1NASA Goddard Institute for Space Studies, 2880 Broadway, New York, USA
  • 2DOE Lawrence Livermore National Laboratory, Livermore, California, USA
  • 3GFDL/NOAA, Princeton University Forrestal Campus, 201 Forrestal Rd., Princeton, New Jersey, USA
  • 4Columbia University, New York, New York, USA
  • 5National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA
  • 6Global Modeling and Assimilation Office, NASA GSFC, Greenbelt, Maryland, USA
  • 7Environmental Modeling Center, NCEP/NWS/NOAA, NCWCP College Park, Maryland, USA

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 US 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 preindustrial era as a target.

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