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PCMDI > Projects > CAPT Printer Friendly Version

CAPT: The Cloud-Associated Parameterizations Testbed

Project Participants
Research Highlights


The Cloud-Associated Parameterizations Testbed (CAPT) aims to diagnose and improve most the representation in climate models of cloud-associated physical processes. In the CAPT, weather forecast techniques are applied to climate models , with an emphasis on the simulations of the Community Atmosphere Model. We will be extending the concept of weather forecasts from the atmosphere to the fully coupled ocean-atmosphere model. Three foci of the project include:

  • Comparing of model simulations to detailed process observations available from the ARM data
  • Diagnosing the origin of errors in model simulations of climate
  • Testing new model parameterizations in order to identify their strengths/weaknesses in simulating cloud-associated processes.

CAPT is a joint project of the Atmospheric System Research (ASR) and Regional and Global Climate Modeling (RGCM) Programs of the U.S. Department of Energy's Office of Science/Biological and Environmental Research (BER). We are using analyses of global weather from numerical weather prediction (NWP) centers, in conjunction with field observations such as those provided by the Atmospheric Radiation Measurement Climate Research Facility, to evaluate parameterizations of sub-gridscale processes in global climate models. Simply stated, we run realistically initialized climate models in forecast mode to determine their initial drift from the NWP analyses and/or from the available field data, thereby gaining insights on model parameterization deficiencies.

Prior to February 2010, CAPT was known as the CCPP-ARM Parameterization Testbed.

Project Participants

Stephen Klein (co-Principal Investigator)
Shaocheng Xie (co-Principal Investigator)

Hsi-Yen Ma
Tom Phillips
Yunyan Zhang
Yuying Zhang
Xue Zheng

Brian Medeiros (collaborator at the National Center for Atmospheric Research)
Dave Williamson (collaborator at the National Center for Atmospheric Research)

Former participants:

Jim Boyle (retired, 2013)
John Tannahill (retired, 2013)
Jerry Potter (retired 2005)
Cecile Hannay (collaborator at the National Center for Atmospheric Research)

Research Highlights


Journal Papers

Technical Reports



From the 1999 Report of the Working Group on Numerical Experimentation (WGNE) on "Transpose AMIP"(1):

"WGNE is continuing to develop the concept of what is termed a "Transpose AMIP", in which climate models would be run in NWP mode, and the evolution of the forecast and of various variables examined, as well as the behaviour of parameterizations before the forecast state diverges too far from the truth. More specifically, predicted variables will be compared with values from reanalyses over regions where these variables are known to be correct from comparison with observations (i.e. data rich areas over the US and/or Europe) in forecasts of only a few days during which the state may be considered 'correct'. The intention is to try and learn why there are model errors, rather than just what the errors are. WGNE recognized that the initialization and spin up of the forecasts were likely to be critical aspects of whether useful results could be obtained, especially in trying to assess model treatments of cloud and radiation. Nevertheless, a pilot project is being undertaken at NCAR with the CCM model using initial data provided by ECMWF (which then have to be interpolated to the CCM grid)." 

and from the 1999-2009 Plan of the European Centre for Medium-Range Weather Forecasts (ECMWF) (2):

"One can have confidence in simulated climate scenarios only if one has confidence in the physical formulations and feed-back loops of the GCMs. A strong case could be made that every GCM should be equipped with a data assimilation system, so that one can diagnose its performance with field experiment data and in medium- and extended-range forecasts." 

- Tony Hollingsworth

  1. WGNE, 1999: Discussion of the 'Transpose AMIP' Project. In Report of the Fourteenth Session of the CAS/JSC Working Group on Numerical Experimentation, CAS/JSC WGNE Report No. 14, pp. 7-8, WMO/TD-No. 964.
  2. ECMWF, 1999: ECMWF Ten-Year Plan, 1999-2009, A. Hollingsworth (ed.)


The CAPT protocol  (see schematic) is analagous to a common NWP approach for development of forecast models.  It is also potentially  useful for diagnosing parameterization problems that may produce systematic model errors on climate time scales . Our goal is to adapt this NWP-inspired technique for its practical application in the development cycles of climate models (Phillips et al. 2004).  

CAPT Flow Diagram


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